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In connection with our discovery of a strong immunosuppressive activity of cyclolinopeptide A (CLA), we investigated immunosuppressive properties of antamanide and a number of its analogues, including symmetrical antamanide, and compared them with the activities of cyclosporin A and CLA. The peptides were investigated by using plaque forming cell (PFC), graft-versus-host (GvH), delayed type hypersensitivity (DTH), and autologous rosette formation cell (ARFC) tests. Antamanide and symmetrical antamanide exhibit an immunosuppressive activity lower than CLA. Linear antamanide fragments are also active. At higher concentrations of the latter peptides, toxic effects occur.

Modulation of protein-protein interactions involved in the immune system by using small molecular mimics of the contact interfaces may lead to the blockage of the autoimmune response and the development of drugs for immunotherapy. The nonpolymorphic Ξ²-regions, exposed to the microenvironment, of the modeled HLA-DQ7, which is genetically linked to autoimmune diseases, were determined. Peptides 132-141 and 58-67, located at the Ξ²1 and Ξ²2 domains of HLA-DQ7, respectively, were tested for their involvement in the interactions with CD4+ T lymphocytes. Linear, cyclic, and dimeric analogs that mimic the exposed surfaces of HLA-DQ7 were designed and synthesized. Their immunosuppressory activities, found in the secondary, humoral immune response to sheep erythrocytes (SRBC) in mice in vitro, ranged from 11% to 53%. The significance of the total charge of the peptides, the pattern of the hydrogen bonding, and the presence of secondary structure were investigated in relation to the immunomodulatory effect of the peptides. Two dimeric analogs of the HLA-DQ7 58-67 fragment, consisting of the two monomers covalently linked by a polyethylene glycol (PEG) spacer, able to mimic the superdimers, were also synthesized and studied. As the 58-67 segment is located at the Ξ²1 region of HLA-DQ7, close to the major histocompatibility complex (MHC) groove, one may assume that the 58-67 peptide could accommodate the association between T-cell receptor (TCR) and human leukocyte antigen (HLA) by activating a co-stimulatory molecule of the TCR/HLA interaction. This hypothesis is supported by the confocal laser image of the fluorescein-labeled 58-67 peptide and by the fact that it is an immunostimulator at low concentration. J. Pept. Sci.

Modulation of protein-protein interactions involved in the immune system by using small molecular mimics of the contact interfaces may lead to the blockage of the autoimmune response and the development of drugs for immunotherapy. The nonpolymorphic beta-regions, exposed to the microenvironment, of the modeled HLA-DQ7, which is genetically linked to autoimmune diseases, were determined. Peptides 132-141 and 58-67, located at the beta(1) and beta(2) domains of HLA-DQ7, respectively, were tested for their involvement in the interactions with CD4(+) T lymphocytes. Linear, cyclic, and dimeric analogs that mimic the exposed surfaces of HLA-DQ7 were designed and synthesized. Their immunosuppressory activities, found in the secondary, humoral immune response to sheep erythrocytes (SRBC) in mice in vitro, ranged from 11% to 53%. The significance of the total charge of the peptides, the pattern of the hydrogen bonding, and the presence of secondary structure were investigated in relation to the immunomodulatory effect of the peptides. Two dimeric analogs of the HLA-DQ7 58-67 fragment, consisting of the two monomers covalently linked by a polyethylene glycol (PEG) spacer, able to mimic the superdimers, were also synthesized and studied. As the 58-67 segment is located at the beta(1), region of HLA-DQ7, close to the major histocompatibility complex (MHC) groove, one may assume that the 58-67 peptide could accommodate the association between T-cell receptor (TCR) and human leukocyte antigen (HLA) by activating a co-stimulatory molecule of the TCR/HLA interaction. This hypothesis is supported by the confocal laser image of the fluorescein-labeled 58-67 peptide and by the fact that it is an immunostimulator at low concentration. Copyright (C) 2009 European Peptide Society and John Wiley & Sons, Ltd. Journal of Peptide Science

Journal of Peptide Science

Alteration of T-cell-associated signal transduction molecules has recently been implicated in immune suppression in tumour-bearing hosts. Here we report the immunoregulatory effects of human lactoferrin (LF) on zeta-chain expression in peripheral blood T lymphocytes from cervical cancer patients and healthy donors. By quantitative flow cytometry analysis, we demonstrated that the mean zeta-chain expression was significantly higher in freshly-isolated T lymphocytes from healthy donors (69%), compared with the patients (38%). Following 3-day culture under standard conditions, zeta-chain expression in T lymphocytes from the patients increased significantly, whereas it dropped in the cells from healthy donors. Anti-CD3 MoAb as well as LF, significantly increased expression of zeta-chain in T cells both from patients and control subjects. The addition of LF to the anti-CD3 MoAb cell cultures resulted in an even higher stimulation of the zeta-chain expression. The results suggest that, in patients with cervical cancer, zeta-chain defects could be corrected by the therapeutic application of LF.

H-2b mice produce insulin-specific antibody when injected with bovine but not porcine or human insulin. Nevertheless, CD4+ T cells have been cloned from C57BL/6 mice primed with porcine, human, and bovine insulin. Here we tested the hypothesis that CD4+ T cells from C57BL/6 mice primed with porcine or human insulin are functionally distinct from those primed with bovine insulin. Our results show that variants of insulin that stimulate antibody responses induced Th2 clones, whereas variants of insulin that fail to stimulate antibody induced Th0 clones. Th0 clones triggered delayed-type hypersensitivity (DTH) in adoptive recipients, whereas Th2 clones did not. Insulin variants that primed Th0 clones also directly primed for DTH responses, while variants that activated Th2 clones did not. Thus, induction of Th2 clones correlated with the ability of mice to make antibody responses to insulin while development of Th0 clones correlated with DTH responses and the failure to produce antibody.

To determine the role of consecutive amino acid residues in the immunoreactivity of the shortest active fragment of PRP, a series of analogs substituted by L-alanine in successive positions of the peptide chain was synthesized. The immunological investigations were carried out in several models: the immune response to T-cell dependent antigen, SRBC (in vivo and in vitro) and to T-cell independent antigen, PVP in vitro. The immunotropic action of the peptide was, in addition, verified with respect to thymocytes forming autologous rosettes. The results of these experiments revealed immunotropic activity (in all tests) of the analog containing alanine instead of proline in position 5 of PRP-pentapeptide.

A proline-rich polypeptide isolated from sheep colostrum is described. The molecular weight of the polypeptide determined by gel filtration is 17 200. However, in the presence of guanidinium chloride the molecular weight found is about 6000. The polypeptide contains about 22% of proline, a high proportion of non-polar amino acids, a low percentage of glycine, and no alanine, arginine and cysteine residues. The only N-terminal amino acid found is leucine. C.d. spectra in water and in 50% (v/v) trifluoroethanol suggest the presence of block sequences of proline residues forming helices of polyproline II type. The proline-rich polypeptide is soluble at 4 degrees C but is reversibly precipitated on warming to room temperature. Maximal precipitation is observed at pH 4.6 and at ionic strength above 0.6. The precipitation depends on the concentration of the polypeptide. No effect of other proteins, Ca2+ and Zn2+ ions on the precipitation of the polypeptide was found. The proline-rich polypeptide is not an amphipathic protein. The lack of effect of the polypeptide on proteolytic enzymes ruled out the possibility that it is an inhibitor of proteinases.