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It has been reported that autoantibodies against the β2-adrenergic receptors are involved in the pathology of allergic disorders and of Chagas' disease. Therefore, the immune response against a peptide (H26Q) corresponding to the putative second extracellular loop of the human β2-adrenergic receptor, which could be a target for autoantibody attack, was analysed in view of its possible immunogenicity. The free peptide induced a T cell-mediated humoral response in the context of three different murine MHC haplotypes. The T cell epitope was found to be localized in the N-terminal region of the peptide. Highly specific T helper cells were capable of stimulating B cells with the potential to generate a large antibody repertoire reactive with the loop peptide. MoAbs were screened to analyse this B cell response for antibodies potentially interfering with receptor function and a MoAb was found that impaired ligand binding to the receptor. [ABSTRACT FROM AUTHOR]

The effect of Trypanosoma cruzi infection on the ability of mature and immature murine peritoneal macrophage (MPM) subpopulations to catabolize the bacteriophage lambda repressor cI protein (cI) has been investigated. The capacity of infected MPM to present the cI and to stimulate various CD4+, I-Ad- or I-Ed-restricted T-cell hybridomas specific for cI was also assessed. Our results show that the radioiodinated cI uptake and catabolism decreased sharply after infection of MPM with T. cruzi. A cI presentation deficiency appeared in mature and immature MPM infected with T. cruzi trypomastigotes. The ability of infected MPM to bind immunogenic cI (12-26) peptides to the plasma membrane Ia molecules was also altered, especially in immature MPM, as shown with paraformaldehyde prefixed MPM, suggesting that these MPM only have a few functional Ia molecules on their membrane. The reduced capacity of cI presentation to the I-Ed-restricted B26. I hybridomas by infected MPM subpopulations was comparable to that of the I-Ad-restricted B24.4 and 826.2 T cells. The percentage of major histocompatibility complex (MHC) class II-positive MPM was also reduced after T. cruzi infection. The percentage of positive interleukin-2 receptor (IL-2R) MPM was sharply lowered in infected cells, even with a pre- or a post-interferon-γ (IFN-γ) activation. Finally, inhibition of prostaglandin with' indomethacin, or of nitric oxide with N-monomethyl-L-arginine, or of tumour necrosis factor-α (TNF-α) with specific monoclonal antibodies did not restore the cI presentation capacities of the MPM subpopulations. Taken together, these results suggest that T. cruzi infection induces a reduced capacity for macrophages to take up and catabolize antigen, resulting in a deficient antigen processing and presentation of the derived immunogenic peptides to specific CD4+ T-helper type-1 cell hybridomas. The decreased cI presenting capacity was a function of the cell's burden and maturity. [ABSTRACT FROM AUTHOR]

CD8+ T lymphocytes are involved in protective immune responses to infected or tumor cells. In this report, we examined the regulation of antigen-specific CD8+ T cell frequency and avidity by distinct Th cell subsets. Peptide-specific CD8+ T cells were induced by immunization of mice with a MHC class I-restricted epitope, co-injected with a MHC class-II restricted epitope to recruit Th cells. CD8+ T cell responses were assessed directly ex vivo for lytic activity and IFN-γ secretion using the enzyme-linked immunospot (ELISPOT) assay. Co-immunization in incomplete Freund's adjuvant (IFA) with three different helper peptides induced IFN-γ- and IL-2-secreting Th cells, in the absence of IL-4 secretion, suggesting preferential Th1 profiles. Such immunization resulted in the increase of antigen-specific CD8+ T cell frequency, which was detected in blood as efficiently as in lymph nodes and spleen, and elicited high-avidity CD8+ T cells. We investigated whether these effects were dependent upon a particular Th profile. When alum was used instead of IFA, the production of IL-2 by Th cells was still significant, while the production of IFN-γ was undetectable. Such Th cell activation failed to support an increase of antigen-specific CD8+ T cell frequency. Altogether, these results document in vivo the regulatory role played by Th cells in CD8+ T cell activation and may be relevant for the design of efficient vaccination schedules. [ABSTRACT FROM PUBLISHER]

Tumor cells can have different morphologic or metabolic phenotypes and display genetic instability. Thus they could also vary in their ability to present epitopes to the immune system. We have analyzed the presentation of H-2 Kb- and Db-restricted cytotoxic T lymphocyte (CTL) epitopes of a tumor-associated antigen by three cell lines derived from hepatocarcinomas developed in vivo by mice transgenic for SV40 T targeted to the liver. SV40 T is the obvious tumor-specific antigen and epitopes derived from this antigen were therefore studied. The study included four already known epitopes that can be presented by SV40-transformed kidney cells and two new CTL epitopes that were identified in the present work. CTL lines specific for each epitope were obtained from C57BL/6 mice and were used to map the presentation of SV40 T peptides by the hepatocarcinoma cells. These tumor cells were derived from the same tissue, induced by the same agent and all naturally presented peptide p232-240 from p53. Despite these common features, they all had different patterns of spontaneous presentation of SV40 T CTL epitopes. The mechanisms underlying this disparity are discussed, together with the possible consequences for establishing immunotherapeutic strategies. [ABSTRACT FROM PUBLISHER]

Polyclonal antibodies were raised in rabbits by immunization with free peptides corresponding to positions 197-222 of the human β1-adrenergic receptor (β1 peptide) and the corresponding sequence (172-197) of the human β2-adrenergic receptor (β2 peptide). While the β2 peptide yielded antibodies that cross-reacted with the β1 peptide, the antibodies against the β1 peptide did not cross-react with the β2 sequence. Cross-reactivity of the anti-β2 peptide antibodies and the selectivity of the anti-β1 peptide antibodies were also revealed in the recognition by immunoblots of the β1- and β2-adrenergic receptors of different species or of the receptor gene products expressed in a bacterial vector. These antibodies could be used immunohistochemically to visualize the β-adrenergic receptors on rabbit heart. The anti-β2 peptide antibodies did not show any functional effect on the β-adrenergic receptors; the anti-β1 peptide antibodies were able to displace agonist affinity to higher values. Recognition of truncated peptides by the anti-β1 and anti-β2 peptide antibodies suggested that the cross-reaction of the anti-β2 peptide antibodies was due to the recognition of a common epitope on the C-terminal part of the peptides. The anti-β1 peptide antibodies recognized the N-terminal part of the peptide better than the C-terminal part. These results suggest that the second extracellular loop postulated in the structure of the human β-adrenergic receptor contains the T and B cell epitopes necessary for induction of an immune response. The selectivity and the functional properties of the antibodies raised against that loop in the β1 adrenergic receptor could have relevance in induction of auto antibodies in certain cardiomyopathic conditions. [ABSTRACT FROM AUTHOR]