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Allelic variations of in vitro HLA class I assembly have been investigated in both the absence and the presence of binding peptides by flow cytometry using human leukocyte antigen (HLA) class I alpha chains isolated by alkali treatment from cultured HLA homozygous B cells and polystyrene beads coated with anti-HLA class I alpha chain antibodies specific to the C-terminal segment (anti-HLA class I beads). The specificity of assembly was temperature dependent, while the stability of the assembled complex depended on the bound peptide. The efficiency of assembly was allele dependent and primarily ruled by the binding affinity of alpha chains with beta(2)m. Thus, an allele hierarchy could be defined for the binding of HLA-B alpha chain with beta(2)-microglobulin: B7, B18B35, B62B27, B51. Allele and temperature dependency was found in HLA class I reassembly on acid treated B cells. The HLA class I proteins, reassembled with specific single peptides, could be efficiently transferred to anti-HLA class I beads. These findings would be used to produce microspheres coupled at high surface density with oriented single-peptide loaded HLA class I molecules and also to improve the preparation efficiency of HLA class I tetramers by the use of site-specific biotinylation.

A new murine monoclonal antibody (MAb), MM4.17, to human multi-drug-resistant (MDR) cells was found to be reactive in an ELISA with a synthetic 16-amino acid peptide selected from the fourth loop of the P-glycoprotein extracellular domain. Immunohistochemistry indicated that this MAb reacted in human tissues in the same pattern as that previously found with other human-specific MAbs to P-glycoprotein. For a precise definition of the MM4.17 epitope, a peptide library consisting of overlapping 4- to 10-mer residues covering the entire P-glycoprotein-fragment was synthesized on polyethylene pins and tested for MAb binding. The results of this ELISA demonstrated that the MM4.17 epitope is constituted by the continuous-linear TRIDDPET amino-acid sequence (residues 750–757 of the human MDR I-P-glycoprotein). The MAb MM4.17 recognizes only the human MDRI -P-glycoprotein isoform, and excess TRIDDPET peptide blocks the binding of the MAb to MDR variants of CEM cells. These results demonstrate that the amino-acid sequence TRIDDPET from the human MDRI gene represents the first continuous-linear epitope identified in the P-glycoprotein extracellular domain.

The viral factor E7 plays a key role in the well-established association between “high-risk” Human Papillomavirus (HPV) infection and the development of epithelial malignant tumors, as uterine cervix and ano-genital cancer. To delve into the molecular mechanisms of HPV-mediated cell transformation, we searched for novel potential cellular targets of the HPV-16 E7 oncoprotein, by means of the yeast two-hybrid technique, identifying a protein–protein interaction between HPV-16 E7 and the pro-apoptotic cellular factor Siva-1. Using co-precipitation assays and the “PepSets” technique, we confirmed this physical interaction and mapped accurately, for both proteins, the amino acid residues involved. Additionally, we found that HPV-16 E7 competed in vitro with the binding of the Bcl-XL anti-apoptotic factor to Siva-1, an interaction that has a major inference in UV radiation-induced apoptosis. In HaCaT immortalized human keratinocytes, forced HPV-16 E7 expression by retroviral infection caused Siva-1 transcript up-regulation, detected by cDNA macroarray hybridization and real-time quantitative PCR, paralleled by an increased amount of protein. Confirming the anti-apoptotic role of HPV-16 E7 in the HaCaT cellular model, evaluated by nuclear morphology, we also found that Siva-1 expression produced a significant increase of the apoptotic rate in UV radiation-exposed HaCaT cells, and that this effect resulted explicitly counteracted by HPV-16 E7. Being apoptosis a key physiological process for the elimination of irreversibly injured cells, the anti-apoptotic role of HPV-16 E7, performed at least by its interference with Siva-1, can be considered an additional mechanism for the survival of damaged, potentially transforming, cell clones. J. Cell. Physiol. 212: 118–125, 2007. © 2007 Wiley-Liss, Inc.

Peptides selected from the HIV viral protein gp120 bind to a synthetic peptide mimicking sequence 78-89 of the human lymphocyte CD4 molecule, linked to activated Sepharose. The binding of viral fragments to the CD4 peptide-Sepharose beads was ascertained either by aid of a ninhydrin reagent or by fluorescence microscopy. A suitable alignment of these HIV peptides with the CD4 fragment showed that multiple interactions might occur between hydrophobic or charged groups of the two molecules. Although this experiment does not demonstrate that these two amino acid stretches are involved in the primary binding of gp120 to CD4 receptors, the present data suggest that the two sequences might have some kind of interaction during subsequent steps of viral infection.

Cell-sized microbeads carrying single peptide-loaded HLA class I molecules were prepared for HLA-A2 and HLA-B7 by a simple procedure which transfers single peptide-loaded HLA class I molecules from cultured cells to polystyrene beads using anti-peptide antibodies directed to an intracellular segment of HLA-A α chains. The surface density of peptide-loaded HLA class I molecules on beads was comparable to that on the peptide-loaded cells. HLA-A2 beads loaded with an HCV peptide HCV1073 were tested for stimulation activity on an HCV1073-specific CD8 + T cell clone NS3-1. A substantial level of γ-IFN production was induced. The stimulation was peptide-specific. The efficiency was dependent on the bead concentration and the surface HLA class I density on beads and enhanced significantly by co-coupling of anti-CD28 to peptide-loaded beads. The peptide-loading efficiency on HLA class I molecules and the transfer efficiency of HLA class I molecules to polystyrene beads were reasonably high for HLA-A2 and HLA-B7. Thus, polystyrene beads carrying these single peptide-loaded HLA class I molecules are potentially useful in further analysis of the co-stimulatory or inhibitory factors involved in CD8 + T cell responses and eventually in detection of cytotoxic T cells in PBLs.

Rabbit antibodies were raised against both long and short peptides derived from exon 7 sequences of human leukocyte antigen (HLA) class I alpha chains; anti-A/B against a 13-mer shared by most HLA-A alpha and HLA-B alpha chains, anti-C against a 15-mer characteristic of HLA-C alpha chains, anti-ACT against a 6-mer specific to HLA-A alpha chains, and anti-CCT against a 5-mer specific to HLA-C alpha chains. Binding activity of the antibodies was determined with peptides by enzyme-linked immunoabsorbent assay (ELISA) and with HLA class I transfectants and the parental cells by FACS analysis. Anti-A/B and anti-C were to a greater or lesser extent crossreactive with the long and short peptides, whereas anti-ACT and anti-CCT were specific to the corresponding short peptides. No binding was seen for anti-ACT and anti-CCT with HLA class I transfectants, C1R-A2, C1R-B7, and 221-Cw1 and the parental cells, C1R (Cw4, E) and 721.221 (E, F). Anti-A/B and anti-C were substantially protein-reactive and the binding order was C1R-B7C1R-A2, 721.221C1R, 221-Cw1 for anti-A/B, and C1R-B7721.221C1R, 221-Cw1, C1R-A2 for anti-C. Thus, anti-A/B and anti-C bound better to HLA-B and HLA-E rather than to HLA-A and HLA-C. Computer modeling of the three-dimensional structure of the intracytoplasmic domains demonstrated that this may be due to structural differences despite the sequence similarities.

The pollen of Parietaria, a weed of the Urticaceae family, is a major cause of respiratory allergy in Europe, where the most common species are P. judaica and P. officinalis. Previously, we reported that a beta-galactosidase fusion protein (6a-BG) expressing a 26-bp cDNA fragment (6a cDNA) contained a dominant IgE-binding epitope (6a epitope) of the major allergens Par o 1 and Par j 1. The present study aimed to define the amino-acid sequence containing the 6a epitope. We analyzed the reactivity of anti-Par o 1 antibodies affinity purified from allergic patient sera with: 1) a panel of synthetic peptides deduced from the 6a nucleotide sequence using different reading frames 2) glutathione S-transferase (GST) fusion proteins containing selected peptides. The peptide NSARARADSCRI (p102) specifically bound anti-Par o 1 antibodies affinity purified from allergic patient sera or from rabbit anti-Par o 1 antiserum (ELISA). The related peptide NSARAGTSSCRI (p101) reacted to human but not to rabbit, anti-Par o 1 antibodies. GST fusion proteins containing p101 (GST 3.5) or p102 (GST 3.2) extensively inhibited the binding between Par o 1 and IgE or IgG antibodies from an allergic patient serum pool according to a dose-response curve. Percent inhibition of IgE antibodies binding obtained by absorbing a solution (50 microl) of affinity-purified antibodies with 5 microg of GST 3.2 or with 1.2 mg of GST 3.5 was 69% and 66%, respectively. In conclusion, the results of the present study indicate that the amino-acid sequences NSARARADSCRI (p102) and NSARAGTSSCRI (p101) contain the dominant epitope of Par o 1 and Par j 1 for human IgE and IgG antibodies indicated as 6a epitope. Moreover, the study shows that the epitope is conserved in recombinant molecules containing these peptides, irrespective of the fused polypeptide (beta-galactosidase or GST). The knowledge of the amino-acid sequence of this dominant epitope is important in therapeutic approaches to the development of allergen-derived haptens.

A new murine monoclonal antibody (MAb), MM6.15, to human MDR1 P-glycoprotein was found to be reactive in ELISA with synthetic peptides selected from the predicted sequences of the first, fourth and sixth extracellular loop of MDRI-P-glycoprotein. In order to precisely define the MM6.15-binding site, a peptide library of overlapping 5- to 9-mer residues covering the entire sixth extracellular loop of both human and rodent class-1 P-glycoproteins was synthesized on polyethylene pins and tested for MAb binding. The results of this ELISA demonstrated that the MAb MM6.15 reacts only with human synthetic peptides and that the critical component of the MAb recognition is made up of the amino-acid sequence LVAHKL (residues 963–968 of the MDRI-P-glycoprotein) with histidine (H), lysine (K) and possibly leucine (L), key residues of this immunogenic domain. © 1995 Wiley-Liss, Inc.

Unfolded HLA class I alpha chains were isolated from B-cell lysates by alkaline denaturation and subsequent gel filtration and used for the detection of HLA class-I-peptide binding. Binding to specific peptides in the presence of excess beta 2-microglobulin induced the unfolded alpha chains to refold and acquire a conformation that is specific to folded alpha chains. This conformational change was measured by a specific RIA that involves inhibition of the binding of 125I-labeled HLA-A2 alpha/beta dimers and rabbit anti-HLA-B7 serum absorbed with beta 2-microglobulin. This assay procedure does not require labeling of either test peptides or test class I proteins and does not seem to have specificity degeneracy. It is applicable to the detection of peptide binding by all HLA class I allelic proteins. Evaluation of the assay conditions and HLA allelic specificity of the peptide binding defined by the use of synthetic peptides are described here, including the technical details, specificity, and reproducibility.

Synthetic peptides selected from HLA-DQ and HLADP glycoproteins were coupled to Sepharose, and used for the isolation of anti-HLA Class II antibodies from the immune sera of rabbits immunized with human lymphoblastoid cells expressing Class II antigens. Antibodies from early and late bleedings displayed remarkable differences in affinity for peptides and for soluble membrane proteins: these differences might be due to an early immune response directed preferentially against surface linear determinants, and to a late response to assembled (discontinuous) sites. The possibility that such antibodies might be used for the identification of amino acid stretches involved in the formation of the same assembled determinant is considered.

Antibodies were raised in 2 rabbits by immunization with carrier proteins covalently bound to deoxyguanosine bearing a 4,4'-dimethoxytriphenylmethyl group protecting the 5'-hydroxy terminus of deoxyribose. After several injections with such complexes, immune sera were tested with an immuno-enzymatic method using as antigens several compounds containing the hapten, as well as synthetic oligonucleotides bearing, or not, this protective group at the 5' terminus. One of the two antisera appeared to recognize the dimethoxytrityl group bound to carrier molecules, and thus might find a useful application for the detection, quantitation, and control of oligonucleotides obtained by automatic synthesis.

Because impaired cellular protease activities are linked to many diseases, such as cancer, inflammation, neurodegeneration, and infection, internally quenched fluorescent peptides have recently been developed as tools for analyzing the specificities of these enzymes. Here we report convenient and cost-effective approaches for the selective "in synthesis" assembly of such substrate peptides for protease assays. Fluorescein and Dabcyl groups were covalently and selectively attached during synthesis to epsilon-amino groups of internal lysines. Functionality was then tested by digestion with leucine aminopeptidase, chymotrypsin, and microsomal vesicles. All peptides proved to be appropriate substrates of the enzymes tested and of the endogenous peptidases in the microsomal vesicles. In summary, we describe an innovative and cheap method to develop completely functional quenched fluorescent peptides that are usable in specific detection of individual proteases, in particular aminopeptidases, in both in vitro and in vivo systems.

We have identified a peptide region on CD18 molecule (the beta subunit of the LFA-1 molecule) involved in syncytia formation of HIV-1-infected lymphocytes. Several phage clones mimicking an epitope of the CD18 cell-surface determinant were isolated from two 9-mer random peptide phage-displayed libraries via their binding to the CD18-specific monoclonal antibody (mAb) MHM23, which in in vitro assay inhibits syncytia formation in HIV-1-infected cells. The peptide sequences displayed on phages that blocked immunolabeling of this mAb on LFA-1-expressing cells were used to identify the epitope recognized by mAb MHM23 by sequence comparison. On the basis of this analysis, two peptides which inhibited syncytia formation in HIV-1-infected cells in vitro were synthesized, thus confirming that they mimic a CD18 domain that is involved in this phenomenon. The results here presented highlight the potential of phage-display technology for the study of biological processes at the basis of virus infection, but also suggest new approaches for the therapy of AIDS.

Protein-reactive, conformation-independent anti-peptide antibodies were raised in rabbits against a C-terminal sequence SDSAQGSDVSLA, common to most HLA-A and -B locus products. Antibodies were coupled to 4.5-microm polystyrene beads through the Fc portion by the use of protein A. The antibody-coupled beads showed a high capacity to bind HLA-A and -B proteins as well as their alpha chains by the intracytoplasmic domain, keeping the extracellular domains solvent exposed. The density of HLA class I proteins bound on the beads was approximately the same as that on cultured B cells. The antibody beads made it possible to quantitate peptide-HLA class I binding, i.e., in vitro HLA class I assembly by flow cytometry. The assembly rate determined by the provisionally called flow cytometric HLA class I assay was 15%-19% for the reassembly of dissociated HLA class I proteins with the released selfpeptides. With single synthetic peptides, the highest rate so far obtained was 6.5%. The assay specificity and reproducibility were satisfactory.

Antibodies were raised in a rabbit by using a 12-residue synthetic peptide, corresponding to fragment 2-13 of rat placental glutathione S-transferase, as the immunogen. The antiserum appeared to react with the fragment as well as with the corresponding human enzyme (GST-pi), which shares with the rat transferase a 92% sequence homology at the N terminus. In addition, the binding of the antibody to the protein was completely inhibited by small amounts of peptide. The enzymatic activity of glutathione transferase was not affected by the antibody. This might indicate that the N-terminal fragment is not involved in the catalytic activity of the enzyme. This antibody of predetermined specificity might thus find a useful application for the detection and approximate quantitation of this marker in human preneoplastic lesions.

Epitope mapping of MDR1-P-glycoprotein using specific monoclonal antibodies (mAbs) may help in delineating P-glycoprotein topology and hence in elucidating the relationship between its structural organization and drug-efflux pump function. In this work, by using synthetic peptide scanning and phage display technologies, the binding sites of the mAb MM12.10, a novel antibody to intact human multidrug resistant (MDR) cells, were studied. The results we obtained confirm that two regions localized on the predicted fourth and sixth loops are indeed external and that MDR1 peptides covering the inner domain of the current 12 transmembrane segment (TMs) model of P-glycoprotein could form part of the MM12.10 epitope.

A new method is described for producing fluorescently-tagged peptides containing specific internal derivatives of lysyl residues. The technique employs the base-labile Boc-Lys(Fmoc)-COOH derivative with base-catalyzed removal of the Fmoc protecting group during peptide synthesis and subsequent fluorescent derivatization of the deprotected ϵ-amino group of lysine. By this technique, other lysine residues and the α-amino group of the fragment remain unmodified, which could have some value in studies where it might be required to tag a single individual lysine residue within the peptide, but not the amino terminus. In spite of the fact that poly-substituted peptides are badly soluble and might seldom find a practical application, this technique also allows the introduction of different fluorochromes at different lysyl residues within the peptide, thus obtaining double fluorescence. The method, fast and easy, requires a limited number of manual operations during the automatic synthesis of peptides. Although peptide synthesizers provided with an oscillating glass reactor are more suitable for the manual interventions described, this technique might be also adapted to the newer instruments utilizing continuous-flow columns.

Antibodies to peptides obtained by synthesis and, to a much lesser extent, prepared by enzymatic digestion of proteins, have been widely used in the last ten years in a variety of immunochemical and biological investigations. There are however several limitations in the correct utilization of such reagents. In fact, in spite of their 'predetermined specificity', antipeptide antibodies often fail to discriminate related molecules, and their reactivity with native proteins may be scarce or even absent, even if the peptide has been selected from surface regions of the protein. Our critical point of view, concerning two main aspects of antipeptide antibody features, i.e. specificity and reactivity, will be presented here, as confronted with information from the available literature. We have selected a restricted number of references among hundreds of publications dealing with antipeptide antibodies: for sure we neglected outstanding papers on the subject, and we apologize in advance.

Seven A2-binding peptides were tested by the HLA class I alpha-chain refolding assay previously described for their direct binding to HLA class I alpha chains derived from a panel of 18 HLA-homozygous B-cell lines of various HLA specificities, including four A2 subtypes: A*0201, A*0204, A*0205, and A*0206. All but one test peptide possessed the major anchor residue motifs, L-V, L-L, or I-L, of A2(A*0201)/A2(A*0205)-binding peptides or the closely related motifs, I-V or V-V. This cell panel analysis confirmed the high A2 allele specificity of the test peptides, but also revealed the existence of a broad cross-binding within the A2 subgroup. Most peptides bound to the alpha chains of the A2 subtypes tested, although their binding patterns showed differences. Furthermore, the A2-binding peptides carrying the I-V or V-V motif were found to cross-react also outside of the A2 subtypes, probably with A24, A26, A28, and A29. Other A-locus allelic products, A1, A3, A11, A30, and A31, and the B-locus allelic products carried by the cells tested were essentially negative, although a few exceptions were seen.

In this study, several methods for controlled labelling of synthetic peptides by the use of fluorescent compounds (fluorescein isothiocyanate and dimethylaminonaphthalene sulfonyl chloride) were investigated. The first reagent yielded monofluoresceinated, active compounds only when the peptides lacked lysine residues. Monolabelling of peptides in solution with dimethylaminonaphthalenesulphonyl chloride was hindered by the broad reactivit of the reagent, but was achieved by reacting the fluorochome on protected resin-bound peptides in solid-phase synthesis. The remarkable stability of the linkage allowed the cleavage of the peptide from the resin and deprotection of side-chain functions without hydrolysis of the labelled group. The binding of antipeptide antibodies to the labelled fragments was then estimated using different techniques.

Synthetic peptides containing amino acid sequence 218–238 of the core protein p24 of human immunodeficiency virus type 1 (HIV-1) and progressively shorter sequences at its C-terminus, were tested for their effect on antigen dependent in vitro responses of peripheral blood lymphocytes (PBL) from normal human donors. A peptide as short as 7 amino acids, corresponding to a highly conserved sequence, was able to inhibit in a dose-dependent manner the induction of a specific primary antibody response to the sheep red cell (SRC) antigen, as well as the proliferative response to recall microbial antigens. The results of this study constitute additional evidence of the immunoinhibitory effects of HIV components and may help to unravel some of the pathogenic mechanisms of AIDS. Moreover, they are of potential relevance for the development of immunoprophylactic and therapeutic strategies.

A new purification procedure for the cytochrome oxidase from Pseudomonas aeruginosa based on immunoaffinity chromatography has been compared with the biochemical method and shown to be (i) fully competitive in terms of chemical homogeneity and enzymatic properties of the purified protein (ii) slightly less efficient in terms of total recovery and (iii) much more convenient in terms of the time required. A further evolution of the method that minimizes the number of purification steps and any stress to the native structure of the protein is suggested.

The amino acid sequences of fragments from the variable and constant regions of rabbit IgG λ-chains from different sources were determined and compared. The peptides had considerable homology with known sequences of human and murine λ-chains and, thus, could be readily aligned. Sequences of corresponding peptides from different sources and preparations reveal differences in the variable as well as the constant region. The latter probably reflect the existence of different alleles and/or isotypes at the c-locus, each coding for a different constant half of the λ-chain. Comparison of the rabbit λ-light-chain sequences with those of human and mouse λ-chains reveals a surprising degree of homology. The amino acid sequences of the peptides reported cover approximately one half of the total sequence of the light chains.

DNA tumor virus oncoproteins bind and inactivate Rb by interfering with the Rb/HDAC1 interaction. Che-1 is a recently identified human Rb binding protein that inhibits the Rb growth suppressing function. Here we show that Che-1 contacts the Rb pocket region and competes with HDAC1 for Rb binding site, removing HDAC1 from the Rb/E2F complex in vitro and from the E2F target promoters in vivo. Che-1 overexpression activates DNA synthesis in quiescent NIH-3T3 cells through HDAC1 displacement. Consistently, Che-1-specific RNA interference affects E2F activity and cell proliferation in human fibroblasts but not in the pocket protein-defective 293 cells. These findings indicate the existence of a pathway of Rb regulation supporting Che-1 as the cellular counterpart of DNA tumor virus oncoproteins.

Sepharose-peptide immunoadsorbents, employed for the isolation of specific antibodies from the sera of rabbits immunized with carrier protein-peptide conjugates, were digested with suitable proteolytic enzymes, in order to obtain the splitting of a part of the peptide bound to the gel. This new modified immunoadsorbent can be advantageously used for the isolation of antibody subsets, that do not cross-react with related peptides exhibiting high sequence homology with the immunogens.

A synthetic approach has been applied to determine the profile of sequential determinants of one immunodominant region of Tissue Polypeptide Antigen (TPA). Five overlapping peptides, covering 30 of the 32 amino acid residues of this fragment, were chemically synthesized, and their antibody-binding activities for rabbit anti-TPA antibodies determined by enzyme-linked immunoadsorbant assays. Anti-TPA reacted with two overlapping fragments at the COOH-terminal end of the fragment, but not with peptides that include Arg 15 considered as essential for the antigenicity of the whole fragment. This might suggest that this critical residue is involved in the formation of a complex conformational determinant.

The partial amino acid sequence of the constant region of the b5 light chain from the normal IgG of a single rabbit is reported. For structure determination, the IgG light chain was fully reduced and carboxymethylated, then digested with chymotrypsin or trypsin. All chymotryptic peptides covering the constant region from positions 116–210 (117–214 in the standardized numbering system of Kabat et al. ∗ ) were isolated and purified by column and paper chromatography. Sequences were then determined using traditional sequencing methods. Overlapping was obtained by use of large tryptic peptides, covering positions 138–210 (139–214 ∗ ). The chymotryptic peptide ending with Leu 115(116 ∗ ) could not be obtained in a pure state owing to insolubility and perhaps heterogeneity. When the sequence of this light chain is compared to those of light chains of b4 and b9 allotypes, about 77% homology is found with b4 and 62% with b9. This confirms serological data which would indicate that b4 and b5 allotypes are more similar to each other in structure than they are to b9. The allotypic differences are distributed throughout the whole constant portion of the light chain.

The partial sequence (positions 29–71) of the variable region of light chains of predominately b5 allotype from the IgG of a single allotype-suppressed rabbit was obtained by traditional sequencing methods on isolated tryptic and chymotryptic peptides. The peptides from this region were isolated in relatively high yields and probably represent a dominant sequence. The framework sequence between positions 35 and 49 (FR 2) is identical to an FR 2 sequence commonly found in light chains from antibodies produced by b4 rabbits as well as murine and human myeloma light chains, with the exception of an interchange of threonine for proline at position 43 or 44. This may be b5 allotype-related since, to date, all the b4 light chains have had proline, and a b9 light chain was found with arginine at position 43. The fact that a dominant sequence could also be found for positions corresponding to the second complementarity determining region (CDR 2, 50–56) in other species, confirms previous observations that this portion of the light chain is not extremely variable in the rabbit.

Rabbit antibodies against small peptides may be composed by subpopulations recognizing different epitopes made likely by few aminoacids. This explains the frequent crossreactivity of antipeptide antibodies with unrelated peptides. A suitable use of immunoadsorbents is suggested to obtain truly specific antibodies able to react with restricted amino acid sequences.

Antibodies against HLA Class II alpha chains were prepared by using as immunogens synthetic peptides selected from the HLA -DQ 1 alpha chains sequence. Antibodies raised against peptide E2 , a 15-residue fragment of the polymorphic first domain, reacted preferentially with cells with the DQ 1 phenotype; however, despite the low sequence homology of this fragment with corresponding segments in DQw2 and DQw3 alpha chains, a partial crossreactivity with cells not expressing the DQw 1 specificity was detected. Antibodies to peptide H , selected from the monomorphic frame, might be specific for DO alloantigens, and presumably do not react with DR antigens. The two peptides, in addition, bind anti-Class II antibodies from the serum of a rabbit immunized with human cells, and appear to represent immunogenic linear determinants in the native glycoprotein molecule.

A general method for the isolation of modified tryptophan-containing peptides is described, which takes advantage of the adsorption properties of tale for aromatic nitrocompounds. The method has been extensively assayed on tryptic and chymotryptic hydrolyzates of human Bence Jones proteins of k and λ type and of human serum albumin, and in preliminary experiments on egg white lysozyme and rabbit IgG light chains. All those proteins had been previously carboxymethylated and modified with 2,4 dinitrophenylsulfenylchloride, a selective reagent for tryptophan.

Three peptides selected from the amino acid sequence of the α- and β-chains of DR2 histocompatibility antigens were chemically synthesized and coupled to carrier proteins to be used as immunogens in rabbits. This immunization resulted in the production of specific antibodies that readily recognized the antigen. However, only one of the four antibody preparations, antibody 6148, elicited by a short peptide from the β-chain (residues 61–73), reacts with native membrane glycoproteins as well as intact human lymphoblastoid cells in enzyme-linked immunosorbant assays. This antibody was found to react also with membrane glycoproteins solubilized by nonionic detergents from cells bearing a different HLA-DR specificity: therefore it is likely that the peptide responsible for eliciting antibody 6148 represents a common framework determinant of DR alloantigens that is accessible on the surface of lymphoblastoid cells. The ability of antibody 6148 to bind to intact cells was confirmed by indirect immunofluorescence and by fluorescein-activated cell sorter analysis. This antibody is also capable of mediating antibody-dependent cellular cytotoxicity as determined by a 51Cr-release assay.

A rabbit was immunized with B lymphoblastoid cells, and subsets of the antibodies produced were isolated on affinity columns made from synthetic peptides corresponding to known amino acid sequences from the human class II antigens DQ and DP. Those peptides for which specific antibodies were isolated could be assumed to contribute to the antigenic properties of the intact antigen. The antibody subsets were tested for binding to synthetic peptides, to glycoprotein fractions isolated from cells with different DR and DQ specificities, and to the cells used for immunization of the rabbit. The isolation of those antibodies directed against well-defined amino acid stretches of the histocompatibility antigens is proof of the role of those regions in determining the antigenic properties of these molecules.

The sequence of the variable region of a light chain from rabbit anti-type III polysaccharide antibody of b4 allotype was determined. Comparison with other sequenced rabbit kappa chains showed striking similarity to light chains with the rare amino terminal sequence Ile-Val-Met from antibodies elicited against Streptococcal A-variant carbohydrate and the carbohydrate of Micrococcus lysodeikticus. Residues 28–33 within the first complementarity determining region (CDR) were identical in sequence to the anti-A-variant carbohydrate antibody light chains but the third CDR differed considerably. An unusual insertion of three amino acids following homology position 58 was found which has not been previously observed in rabbit kappa chains.

The work reported here concerns the specificty of four antibodies elicited by synthetic peptides corresponding to three domains of the HLA-B7 glycoprotein, and one of the β2 microglobulin. One of the four peptides had been previously investigated, but the data obtained by its elicited antibodies were uncomplete. Of the three HLA-B7 peptides assayed, one was unable to raise an immune response. The other two produced antibodies in good titer that reacted with the antigen peptide, but were unable to recognize antigenic determinants when tested on membrane glycoproteins solubilized from human lymphoblastoid cells. In contract, the antibody elicited by the only fragment from the β2microglobulin recognized the native β2microglobulin molecule as well as HLA/β2m com­plexes, and reacted with intact human cells, as determined by ELISA and by FACS analysis. This peptide, which contains one of the most hydrophylic fragment of the whole molecule, is likely an important antigenic site, since it is also recognized by traditional antisera raised against native β2 microglobulin.

Peptides containing tryptophan 146 from rabbit kappa light chains of b5 and b6 allotypes were Isolated and their sequences determined. Between positions 138 and 161 there is 56% homology between b4 and b9, 64% homology between b5 and b9 and 80% homology between b4 and b5. Between positions 138 and 150 there is 86% homology between b4 and b6 and 93% homology between b5 and b6. This confirms the predictions of serological studies that b9 light chain constant regions would differ most from the other allotypes, while b5 and b6 would be most similar.

T cells recognize protein antigens as fragments (peptides) held in a defined binding site of class I or class II major histocompatibility (MHC) molecules. The formation of complexes between various immunologically active peptides and different MHC molecules has been demonstrated directly in binding studies between the peptides and solubilized, purified molecules of class II MHC. Studies with intact cells, living or fixed, have not directly demonstrated the binding of the peptides to MHC molecules on antigen-presenting cells, but the formation of such complexes has been shown indirectly through the capacity of antigen-presenting cells to stimulate specific T cells. Here we report evidence that supports directly the binding of radiolabelled influenza matrix peptide 17-29 to products of the human class II MHC locus HLA-DR, on living homozygous B-cell lines, and we show that the kinetics of such binding is much faster with living cells than with fixed cells. Furthermore, whereas the peptide reacts with HLA-DR molecules of all alleles, it binds preferentially to DR1, the restricting element in antigen presentation.

The amino acid sequence of the light chain from a specifically purified rabbit (No. 2717) anti- p -azobenzoate antibody preparation (b4 allotype) of restricted heterogeneity has been determined. This light chain is composed of 216 residues, including seven half-cystine residues located at positions 23, 80, 88, 134, 171, 194 and 216. Three intrachain disulfide bonds appear to be present in contrast to only two disulfide bonds as has been so far described for Bence Jones protein and light chains of human and mouse. This light chain was sequenced by isolating the tryptic peptides, sequencing the peptides and establishing their order within the molecule. Unambiguous identification of the overlaps was achieved by taking into account the partially characterized tryptic peptides from citraconic anhydride-treated light chains and chymotryptic and peptic peptides from digests of both untreated and citraconylated light chains. Comparison of this amino acid sequence with the amino acid sequence of the car☐ylterminal half of the b4 light chains from unimmunized rabbits reveals differences at positions 165, 166, 169 and 176 indicating the existence of more than one sequence in the b4 “constant” region. There is substantial sequence homology between the variable half of 2717 light chain and human Bence Jones protein. Indeed, 46 positions in the V region (42%) are occupied by the same residues in this light chain and in human subgroup V κIII .

Light chains have been isolated following sulfitolysis and gel filtration of immunoglobulin G from allotype-suppressed b9 homozygous rabbits. Chemically and immunologically all light chains belong to the λ type, exist only in the form with two disulfide infrachain bridges, and seem to be very similar to the b negative, λ-type light chains which all allotype synthesize, in very low amount, under normal circumstances.

A mouse monoclonal antibody reacting in ELISA with a synthetic peptide representing a linear amino acid stretch of the protein antigen was tested on all overlap­ ping 5-mer to 9-mer fragments of the peptide, as prepared by multi-pin synthesis. Analysis of the binding data suggests that several residues in the peptide might be relatively unrelevant for recognition, while few others seem to play a critical role as key residues. On the basis of such observations, we attempted to reconstruct an alternative essential epitope by introducing multiple amino acid substitutions in the 9-mer peptide exhibiting the best binding activity, and then tested its ability to be recognized by the monoclonal antibody.