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Improved detection of anti-carbohydrate antibodies is a need in clinical identification of biomarkers for cancer cells or pathogens. Here, we report a new ELISA approach for the detection of specific immunoglobulins (IgGs) against carbohydrates. Two nanometer gold glyconanoparticles bearing oligosaccharide epitopes of HIV or Streptococcus pneumoniae were used as antigens to coat ELISA-plates. A ~3,000-fold improved detection of specific IgGs in mice immunized against S. pneumoniae respect to the well known BSA-glycoconjugate ELISA was achieved. Moreover, these multivalent glyconanoparticles have been employed in solid phase assays to detect the carbohydrate-dependent binding of human dendritic cells and the lectin DC-SIGN. Multivalent glyconanoparticles in ELISA provide a versatile, easy and highly sensitive method to detect and quantify the binding of glycan to proteins and to facilitate the identification of biomarkers.

Aims: Coupling of capsular polysaccharides of pathogens to immunogenic protein carriers (conjugate vaccines) improves carbohydrate immune response. Our idea is to explore gold nanoclusters as carriers to prepare fully synthetic carbohydrate vaccines., Materials & Methods: Gold glyconanoparticles bearing a synthetic tetrasaccharide epitope related to the Streptococcus pneumoniae type 14 capsular polysaccharide (Pn14PS), the T-helper ovalbumin 323-339 peptide (OVA(323-339)), and D-glucose were prepared by a one-pot method. Their immunogenicity was tested in mice. Cytokine levels after spleen cell stimulation with OVA(323-339) were analyzed using a luminex-multiplex cytokine assay. The capacity of the evoked antibodies to promote the uptake of S. pneumoniae type 14 by leukocytes was assessed., Results & Discussion: Glyconanoparticles containing 45% of tetrasaccharide and 5% OVA(323-339) triggered specific anti-Pn14PS IgG antibodies. Cytokine levels confirmed that glyconanoparticles led to T-helper cell activation. The anti-saccharide antibodies promoted the phagocytosis of type 14 bacteria by human leukocytes, indicating the functionality of the antibodies., Conclusion: Gold nanoparticles have great potential as carriers for the development of a great diversity of fully synthetic carbohydrate-based vaccines.

Memory formation to CRM-neoglycoconjugate, a synthetic branched tetrasaccharide of Streptococcus pneumoniae type 14 polysaccharide (Pn14PS) that is conjugated to a CRM197 protein, was investigated using mice models. Mice were first immunized with the CRM-neoglycoconjugate and then boosted with either the same neoglycoconjugate or a native Pn14PS in order to investigate the effect of booster immunization. Boosting with the CRM-neoglycoconjugate resulted in increased levels of interleukin 5 (IL-5) in the serum on Day 1, followed by the appearance of high levels of specific anti-Pn14PS IgG antibodies on Day 7. Boosting with native Pn14PS resulted in neither IL-5 induction nor the generation of anti-Pn14PS IgG antibodies. In vitro (re)stimulation of spleen cells after booster injection with the neoglycoconjugate revealed the presence of IL-4 and IL-5. This was not seen in spleen cells obtained from mice boosted with the polysaccharide. When stimulated with heat-inactivated bacteria, however, the polysaccharide-boosted mice did have higher levels of IFN-γ and lower levels of IL-17 than both the CRM-neoglycoconjugate-boosted mice and the mock-immunized mice. In conclusion, neoglycoconjugate boosting is responsible for the activation of memory cells and the establishment of sustained immunity. Not only is a booster with native polysaccharide ineffective in inducing opsonic antibodies, but it also interferes with several immunoregulatory mechanisms., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

A series of nonformulated adjuvants, i.e. Quil-A, MPL, DDA, CpG and Alum were codelivered with a synthetic branched tetrasaccharide fragment corresponding to Streptococcus pneumoniae type 14 polysaccharide (Pn14PS) conjugated to CRM(197) in order to investigate antibody- and cell-mediated immune responses in a mouse model. The first immunization was performed intracutaneously in the presence of adjuvants. Booster injections which were given without adjuvant dramatically enhanced and expanded the immune response from IgM to IgG1 and other IgG subclasses. Codelivery of the neoglycoconjugate with CpG or Alum had no additional effect over vaccine in saline, and elicited mainly IgG1 antibodies against Pn14PS. CpG even has a modest suppressive effect on the antibody response. Codelivery of the neoglycoconjugate with Quil-A, MPL, DDA alone or in combination resulted in both IgG1, IgG2a, IgG2b and IgG3 antibodies. Quil-A alone or in combination with MPL induced systemic IL-5 and IL-6 6h after primary immunization. This adjuvant combination also increased CD4/CD8 T cells ratio in lymph nodes and peripheral blood on day 1 after immunization. Seven days later, the ratios in blood and lymph nodes had returned to normal. In conclusion, codelivery of Quil-A alone or in combination with MPL had the most dramatic effect on antibody- and cell-mediated immune response to neoglycoconjugate of Pn14PS., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

Synthetic overlapping oligosaccharide fragments of Streptococcus pneumoniae serotype 14 capsular polysaccharide (Pn14PS), [6)-[beta-D-Galp-(1-->4)-]beta-D-GlcpNAc-(1-->3)-beta-D-Galp-(1-->4)-beta-D-Glcp-(1-->](n), were conjugated to CRM(197) protein and injected into mice to determine the smallest immunogenic structure. The resulting antibodies were then tested for Pn14PS specificity and for their capacity to promote the phagocytosis of S. pneumoniae type 14 bacteria. Earlier studies have reported that the oligosaccharide corresponding to one structural repeating unit of Pn14PS, i.e., Gal-Glc-(Gal-)GlcNAc, induces a specific antibody response to Pn14PS. The broader study described here, which evaluated 16 oligosaccharides, showed that the branched trisaccharide element Glc-(Gal-)GlcNAc is essential in inducing Pn14PS-specific antibodies and that the neighboring galactose unit at the nonreducing end contributes clearly to the immunogenicity of the epitope. Only the oligosaccharide conjugates that produce antibodies recognizing Pn14PS were capable of promoting the phagocytosis of S. pneumoniae type 14. In conclusion, the branched tetrasaccharide Gal-Glc-(Gal-)GlcNAc may be a serious candidate for a synthetic oligosaccharide conjugate vaccine against infections caused by S. pneumoniae type 14.

Host protection against Streptococcus pneumoniae is mainly mediated by opsonin-dependent phagocytosis. Several techniques for measuring opsonophagocytic activity (OPA) of antibodies to S. pneumoniae have been standardized and used. These include the viable cell-assay, flow-cytometric assays, and an assay utilizing radiolabeled bacteria. Using these different methods, we measured the OPA of antibodies to S. pneumoniae types 6B and 19F from the sera of infants immunized with a pneumococcal conjugate vaccine, PncCRM. Generally, the results obtained by the various techniques correlated well, although serotype-specific differences were found (6B, r = 0.78 to 0.95, P < 0.001; 19F, r = 0.50 to 0.84, P < 0.001). The same serotype-specific differences were observed for the relationship between the concentrations of specific immunoglobulin G antibodies measured by enzyme immunoassay and the OPA. Since the sensitivities of the OPA assays differed, the most prominent discrepancies between the techniques were found at low antibody concentrations.

The immunogenicity and protective capacity of Streptococcus pneumoniae 6B capsular polysaccharide (PS)-derived synthetic phosphate-containing disaccharide (Rha-ribitol-P-), trisaccharide (ribitol-P-Gal-Glc-), and tetrasaccharide (Rha-ribitol-P-Gal-Glc-)-protein conjugates in rabbits and mice were studied. In rabbits, all saccharides conjugated to keyhole limpet hemocyanin (KLH) evoked high levels of pneumococcal (Pn) type 6B antibodies that facilitated type-specific phagocytosis. Unlike the disaccharide rabbit antisera, tri- and tetrasaccharide rabbit antisera also reacted with 6A PS in an enzyme-linked immunosorbent assay (ELISA) and promoted phagocytosis of 6A pneumococci. All these rabbit antisera passively protected mice against a Pn 6B challenge. The disaccharide conjugate-induced antiserum, however, failed to protect mice against a 6A challenge. In mice, phagocytic and protective anti-Pn 6B antibodies were only induced by the tetrasaccharide conjugate and not by PS 6B or PS 6B-protein conjugates. These antibodies did not cross-react with 6A PS in ELISA and were unable to phagocytize 6A pneumococci. In conclusion, the disaccharide and tetrasaccharide conjugates already contain epitopes capable of inducing 6B-specific, fully protective antibodies in rabbits and mice, respectively.

Fcgamma receptors show two genetically determined polymorphisms: the biallelic FcgammaRIIa-R131 and -H131 polymorphism and the NA1/NA2 FcgammaIIIb polymorphism. Using 10 pre- and postconjugate vaccination sera from adults, we analyzed in vitro phagocytic capacities of three different combinations of polymorphonuclear leukocyte FcgammaR allotypes: those homozygous for the H131 and NA1 allotype, those homozygous for the R131 and NA2 allotype, and those heterozygous for both receptors. For pre- and postvaccination sera, mean phagocytosis levels for the homozygous H131/NA1 allotype were 4 -fold higher than for the homozygous R131/NA2 allotype. There was a strong and significant correlation between IgG2 ELISA antibody titers and phagocytosis levels for the homozygous H131/NA1 Fcgamma receptor allotype and the heterozygous allotype but not for the homozygous R131/NA2 allotype. There was no relation between IgG1 ELISA titer and phagocytosis level. Apparently the IgG2 antibodies induced are functionally the most important. This may explain the large effect of Fcgamma receptor polymorphisms on in vitro phagocytosis of pneumococci mediated by conjugate antisera.

A phagocytosis assay for Streptococcus pneumoniae based on flow cytometry (FACS) with human polymorphonuclear cells and human complement was developed for the study of human vaccination antisera. Human prevaccination sera already contain high levels of C-polysaccharide (C-PS) antibodies, which are not protective in humans but which might give false positive results in a flow-cytometry-based assay. Cultures of S. pneumoniae grown to log phase on three consecutive days, followed by heat inactivation, yielded stable and highly encapsulated strains for serotypes 6A, 6B, 14, 19F, and 23F. As a result, only serotype-specific antibodies were able to facilitate phagocytosis of these strains, whereas no phagocytosis was observed with antibodies against C-PS or pneumococcal surface proteins. No, or weak, phagocytosis was observed with human prevaccination sera, whereas in general, postvaccination antisera facilitated phagocytosis. A highly significant correlation was observed between enzyme-linked immunosorbent assay titers and FACS phagocytosis titers (r = 0.98, P < 0.001) for serotype 23F pneumococci with human vaccination antisera. For all serotypes, interassay variation was below 10%. Major advantages of this assay over the classical killing assay are that (i) limited amounts of sera are required (10 microliter per titration curve), (ii) 600 samples can be processed in one day by one person, and (iii) cells can be fixed and measurement of the samples can be performed up to 1 week later.

Although pneumococcal conjugate vaccines are close to being licensed, a more profound knowledge of the virulence factors responsible for the morbidity and mortality caused by Streptococcus pneumoniae is necessary. This review deals with the major structures of pneumococci involved in the pathogenesis of pneumococcal disease and their interference with the defense mechanisms of the host. It is well known that protection against S. pneumoniae is the result of phagocytosis of invading pathogens. For this process, complement and anticapsular polysaccharide antibodies are required. Besides, relatively recent experimental data suggest that protection is also mediated by the removal of disintegrating pneumococci and their degradation products (cell wall, pneumolysin). These structures seem to be major contributors to illness and death caused by pneumococci. An effective conjugate vaccine should therefore preferably include the capsular polysaccharide and at least one of these inflammatory factors.

Relationships between in vitro parameters (opsonic activity and anti-pneumococcal polysaccharide [PS] antibody subclasses) and in vivo mouse protection were established by logistic regression analysis. Data were from 158 mice challenged with pneumococci after vaccination with synthetic oligosaccharide- and PS-protein conjugates in combination with the adjuvant Quil A. The hypothesis that serum opsonic activity has predictive value for protection against pneumococcal infection was tested. Serum opsonic activity was well correlated with protection (chi 2 = 35.5, P < 0.001), although a stronger correlation was observed for anti-PS IgM and IgG. The combined use of IgG and opsonic activity as predictor variables yielded the best fitting model for predicting protection (chi 2 = 74.1, P < 0.001). When opsonic activity data were added to models that included various antibody isotypes, the statistical significance of the models was enhanced. Thus, the opsonic activity of antisera induced by pneumococcal vaccines can predict mouse protection.

The adjuvant effect of Quil A on the primary antibody response of mice to pneumococcal capsular polysaccharide conjugates was examined. Quil A increased the anti-capsular polysaccharide antibody titres, the protection against Streptococcus pneumoniae, and the opsonic capacity of the antibodies as measured in a newly developed in vitro phagocytosis assay, using the mouse macrophage cell line J774.

Streptococcus pneumoniae type 23F capsular polysaccharide (PS23F) consitss of a repeating glycerol-phosphorylated branched tetrasaccharide. The immunogenicities of the following related antigens were investigated: (i) a synthetic trisaccharide comprising the backbone of one repeating unit, (ii) a synthetic tetrasaccharide comprising the complete repeating unit, and (iii) native PS23F (all three conjugated to keyhole limpet hemocyanin [KLH]) and (iv) formalin-killed S. pneumoniae 23F. All antigens except the trisaccharide-KLH conjugate induced relatively high anti-PS23F antibody levels in rabbits. The epitope specificity of such antibodies was then studied by means of an inhibition immunoassay. The alpha(1-->2)-linked L-rhamnose branch was shown to be immunodominant for immunoglobulin G (IgG) induced by tetrasaccharide-KLH, PS23F-KLH, and killed S. pneumoniae 23F: in most sera L-rhamnose totally inhibited the binding of IgG to PS23F. Thus, there appears to be no major difference in epitope specificity between IgG induced by tetrasaccharide-KLH and that induced by antigens containing the polymeric form of PS23F. Human anti-PS23F IgG (either vaccine induced or naturally acquired) had a different epitope specificity: none of the inhibitors used, including L-rhamnose and tetrasaccharide-KLH, exhibited substantial inhibition. These observations suggest that the epitope recognized by human IgG on PS23F is larger than the epitope recognized by rabbit IgG. Both human and rabbit antisera efficiently opsonized type 23F pneumococci, as measured in a phagocytosis assay using human polymorphonuclear leukocytes.

Overlapping synthetic disaccharide, trisaccharide and tetrasaccharide, derived from pneumococcal polysaccharide type 17F (PS17F), were coupled to keyhole limpet haemocyanin (KLH). The conjugates were tested in mice. The disaccharide-KLH and especially trisaccharide-KLH, in combination with Quil A, induced high titres of high-avidity anti-PS17F IgG. Both conjugates protected mice against challenge with Streptococcus pneumoniae 17F. Tetrasaccharide-KLH, although able to elicit anti-tetrasaccharide antibodies, induced a minimal non-protective anti-PS17F IgG response of low avidity. The tetrasaccharide-KLH conjugate, in contrast to the other conjugates, failed to bind rabbit anti-PS17F IgG.

This project investigated the effects of novel carriers and adjuvants on the isotype of murine immunoglobulin G (IgG) antibody to pneumococcal capsular polysaccharide type 14 (S14PS). S14PS conjugated to bovine serum albumin induced a weak antibody response which was 100% IgG1 following injection without adjuvant. The same polysaccharide conjugated to flagella of Salmonella typhi induced an antibody response which was 88% IgG3. S14PS-bovine serum albumin was injected with block copolymer L121 or Quil A in squalane-in-water emulsions. The copolymer L121 was at least as effective as Quil A or complete Freund adjuvant in inducing IgG antibodies. IgG1 was the dominant subclass for all. Addition of monophosphoryl lipid A, but not the threonyl derivative of muramyl dipeptide or nontoxic Rhodopseudomonas sphaeroides lipopolysaccharide, to copolymer L121 increased production of the IgG2a, IgG2b, and IgG3 subclasses. S14PS-flagella with copolymer L121 induced higher titers with a markedly altered isotype distribution: 13% IgG1, 52% IgG2a, 6% IgG2b, and 29% IgG3. Monophosphoryl lipid A added to L121 reduced IgG1 antibody to 5%, but increased IgG2a antibody to 14%, IgG2b antibody to 3%, and IgG3 antibody to 78%. These studies demonstrate that both the carrier and the adjuvant can influence the titer and isotype distribution of antipolysaccharide antibody responses.

A Streptococcus pneumoniae type 14-specific ELISA and ELISPOT assay have been developed based on the use of biotinylated type 14 capsular polysaccharide (S14PS-biotin). A major advantage of this application over other methods is the use of 10-100-fold less antigen than that reported in the literature for other similar assays. Moreover, the prepared biotinylated polysaccharides are very stable and it is possible to use the same procedures for other pneumococcal polysaccharide antigens (e.g., S6BPS) with no major changes necessary in the ELISA and ELISPOT protocols. Furthermore, a simple thin layer chromatography method has been developed as a method for quality control of the biotinylated polysaccharide. Immunization with the thymus-independent antigen S14PS resulted in the induction of IgM spot-forming cells (SFC) and antibodies while S14PS-protein conjugates induced a thymus-dependent response. The immune response to the conjugates was enhanced by the addition of the adjuvant Quil A resulting in high levels of both IgG SFC and antibodies at day 14 after immunization. The developed assays are reliable and reproducible tools for studying the humoral immune response against Streptococcus pneumoniae type 14 capsular polysaccharide derived antigens.

Incorporated in oil-in-water emulsions, nonionic block polymer surfactants change the kinetics of generated antibody responses against pneumococcal hexasaccharide-protein conjugates: prolonged immunoglobulin M and immunoglobulin G responses are realized. Nonionic block polymer surfactants favor the immunogenicity of hexasaccharide-protein conjugates in young mice in such a way that a single injection yields long-lasting protection.

The reliability of the determination of antibody avidity in polyclonal sera by indirect sandwich ELISA was studied. Binding of IgM and IgG (sub)classes in unpurified serum to Streptococcus pneumoniae type 3 capsular polysaccharide, which was coated onto ELISA plates, was inhibited with different inhibitors. The inhibitor concn at which 50% inhibition of antibody binding to the ELISA coat was achieved, was used as a measure for antibody avidity. As this 50% inhibition value is dependent upon the dilution of the serum and thus upon the initial amount of free antibody, it is necessary to define (a narrow range of) final ELISA absorbance values to which the dilutions of non-inhibited sera have to be adjusted. The shapes of the serum dilution curves have a good correlation with the numerical 50% inhibition values of the antibody avidity. The inhibition ELISA is suitable to compare the avidity values of the different antibody isotypes, but two remarks should be made: (1) antibody heterogeneity should be considered to influence the results and prevent the accurate measurement of absolute numerical avidity values. Because in the ELISA system merely antibody "activity" is measured, comparison of the efficacy of vaccines by means of the 50% inhibition (avidity) value of various antibody (sub)classes can still be performed in a reliable way; (2) results of the determination of the 50% inhibition values of the different antibody (sub)classes showed them to be dependent on the molecular ratio between antibody (sub)class levels. More aspects of the determination should be taken into account, like shapes of simple dilution curves, influences of various inhibitor concns in the diluent and whole (extended) inhibition curves.

Avidities of antibody (sub)classes in polyclonal antisera against Streptococcus pneumoniae type 3 (S3) can be (semi) quantitatively determined with a specific inhibition ELISA. A hexasaccharide was isolated from the hydrolyzed S3 capsular polysaccharide and coupled to a protein-carrier. Mixtures containing these conjugates and nonionic block polymer (NBP) surfactants were used for immunization. After various immunizations of these conjugates without NBP the anti-S3 specific antibodies of IgM and IgG2a isotype decreased in both antibody level and avidity. The adjuvants NBP 1501 and L121 not only enhanced the hexasaccharide-protein induced IgM and IgG antibody levels but also clearly increased the avidity of the two antibody (sub)classes IgM and IgG2a. This effect was observed in normal (data not shown) and X-linked immunodefective mice. A maturation of the IgG antibody response was realized by the second immunization with hexasaccharide-protein conjugate whereas the third immunization showed no further increase in antibody level and avidity.

Streptococcus pneumoniae type 14 capsular polysaccharide-bovine serum albumin (S14PS-BSA) conjugates were prepared by water-soluble-carbodiimide-mediated condensation with or without the use of N-hydroxy-sulfosuccinimide. The immunogenicities of the capsular polysaccharide (S14PS) and of the conjugates were studied in (CBA/N x BALB/c)F1 mice and in female BALB/c mice. The response in these mice indicates that S14PS could be classified as a thymus-independent type 2 antigen. Coupling of S14PS to BSA improved the immunogenicity of this polysaccharide, and an immunoglobulin G memory response was evoked. Conjugation with N-hydroxysulfosuccinimide resulted in a product with a higher polysaccharide/protein ratio. This conjugate induced a greater immune response than did the classical conjugate. Quil A enhanced the immune response to S14PS and to most S14PS-BSA conjugates. The enhancement of the immune response to the conjugates seemed to depend on the coupling procedure. Our results indicate that for the construction of immunostimulating complexes based on polysaccharide or oligosaccharide-protein conjugates, attention should be paid to the degree of cross-linking of the antigens involved.

Nonionic block polymer surfactants (NBPs) were tested for the capacity to stimulate the antibody response against hexasaccharide (HS), derived from Streptococcus pneumoniae type 3 capsular polysaccharide (S3PS), which was conjugated to proteins. The immune response was evaluated in the (CBA/N x BALB/c)F1 progeny, in which female mice are phenotypically normal whereas male mice carry an X-chromosome-linked immunodeficiency. NBPs L101, L121, 1101, and 1501 were able to increase anti-HS immunoglobulin M (IgM) and IgG levels in both normal and X-chromosome-linked immunodeficient mice (with up to 74-fold stimulation of antibody titers). Distribution of S3PS-specific antibodies over the various IgG isotypes was restricted after immunization with either HS-bovine serum albumin or HS-keyhole limpet hemocyanin (HS-KLH). Addition of NBPs (in particular 1501) resulted in a more diverse immune response with either antigen as judged by isotype distribution. Isoelectric focusing of individual sera and subsequent detection of S3PS-binding antibodies in these sera by immunochemical staining revealed a restricted number of different spectrotypes in the course of the immune response. Upon immunization of mice with HS-KLH, spectra of secreted antibodies were slightly more complex and more densely stained than after immunization with HS-bovine serum albumin. Furthermore, NBPs 1101 and 1501 appeared to be able to stimulate the secretion of antibodies, which were secreted only in small amounts without the use of NBPs. Different explanations for increased spectrotype diversity after immunization with KLH as the carrier and after administration of NBPs as the adjuvant are discussed.

A sensitive ELISA has been developed to study immune responses in mice against Streptococcus pneumoniae type 3 capsular polysaccharide (S3PS) and hexasaccharide (HS)-protein conjugates derived therefrom. An advantage of the described system is that the same microtiter plates can be used for both ELISA and ELISPOT tests with a standardized washing procedure and diluent composition. S3PS induced predominantly IgM antibodies and minute amounts of IgG as measured by ELISA in serum. This was accompanied by large numbers (greater than 14000) of IgM spot-forming cells in the spleen. A shift towards IgG production was achieved by addition of lipid A. HS-protein conjugates induced predominantly IgG antibodies after booster immunization(s). Furthermore these conjugates induced large numbers (greater than 40000) of IgG spot-forming cells (SFC) in the spleen. ELISA and ELISPOT assays on microtiter plates are both reliable and highly reproducible assays for the evaluation of immune responses to S. pneumoniae antigens.

A semisynthetic vaccine to Streptococcus pneumoniae type 3 has been developed. The hexasaccharide [leads to 3)GlcpA beta(1 leads to 4)Glcp beta(1 leads to]3 was isolated from a partial acid hydrolysate of the capsular polysaccharide S3. It was coupled to stearylamine by reductamination with NaCNBH3 and then incorporated into liposomes. These haptenated liposomes were tested for immunogenicity in mice. They induced protection to a lethal dose (25 50% lethal doses) of S. pneumoniae type 3 and gave rise to immunoglobulin M antibodies. No cross-protection was observed against S. pneumoniae type 11.