T-cell clone anti-clone interactions. Effects on suppressor and helper activities

Cytotoxic T-cell role in renal allograft rejection and regulation. Renal allograft infiltrating cytotoxic T-cell line with suppressor-inducer function

We previously investigated the characteristics of renal allograft infiltrating T-cell lines that were propagated from biopsy and nephrectomy specimens designated as IG-Bip and IG-Neph, respectively, or analogous line designated IG-T-eff, which was generated by co-culturing pretransplant recipient blood with irradiated donor splenocytes (manuscript submitted). The recipient (IG) had no previous sensitization to donor mismatched HLA antigens (A2 and DR1). Phenotypically, all lines were of recipient origin and were CD3+, TCR alpha beta +, DR+. However IG-Bip line was low in CD4 (19%) and high in CD8 (50%), whereas IG-Neph and IG-T-eff lines had equal mixture of CD4+ (34%) and CD8+ (38%) subsets). Functionally, all three lines contained donor-specific CTLs. In the present report, we used the in vitro MLR to examine the possible utilization of these CTL lines as inducer cells to generate donor-specific Ts cells from recipient PBLs. Coculturing IG-PBL that was drawn before or after transplantation and immunosuppression with irradiated IG-T-eff or IG-Neph but not IG-Bip CTL lines, generated Ts cells. Ts cells were of recipient origin and were CD3+, CD8+, leu 11b+, CD28-, all characteristic of Ts-effector phenotype. Ts cells inhibited MLR response of recipient PBLs against donor or third-party stimulators that shared with the donor the mismatched HLA antigens. Ts suppression was more pronounced against early phase of MLR response and was not due to a shift in MLR kinetics or nonspecific soluble suppressor or cytotoxic products. These findings suggest that allograft infiltrating CTLs or their in vitro generated analogous line may modulate allograft rejection by acting as Ts inducers and that Ts induction was dependent on the presence of the CD4 subset within the Ts-inducer cells but was not dependent on renal transplantation or immunosuppression.

Regulatory interactions among autologous T cell clones. Human bifunctional T cell clones regulate the activity of an autologous T cell clone

In contrast to the ease of cloning and characterizing, at the molecular level, helper and cytotoxic T cells, suppressor T cells remain an enigma, and their existence as discrete entities is being increasingly challenged. Here we review evidence that CD4+ regulatory clones, capable of expressing both helper and suppressor functions, may account for much of the suppressor function. It is suggested that a single T cell clone, depending on the signals it receives from its environment, may release either helper or suppressor cytokines. Studying such clones under defined conditions (providing suppressor signals), may preclude detection of their helper capacity. Since some therapeutic approaches in various human diseases are based on the manipulation of helper and suppressor functions, the question whether committed suppressor cells exist has important practical implications in medicine.

Regulation of autoimmunity

Despite the prevalence of self-reactive T cells, the healthy organism is not in a state of all-out war. Potent regulatory mechanisms exist at every level to permit the successful integration of the various aspects of the immune system, allowing only minor skirmishes, which ordinarily can be neutralized.

Specific interactions between a human CD4+ clone and autologous CD4+ bifunctional immunoregulatory clones

The cellular communications between a human CD4+ clone and autologous CD4+ clones induced with the first clone are described. The autoreactive clones proliferated after stimulation with the inducer clone, but not after stimulation with autologous clones expressing irrelevant specificities. The inducer clone markedly lost its ability to interact with the autoreactive clones after the modulation of its T-cell receptor. The proliferation of the autoreactive clones stimulated with the inducer clone was blocked by anti-DR monoclonal antibody. Collectively, these findings indicate that the autoreactive clones recognize idiotypic-like determinants on the receptor of the inducer clone in conjunction with DR antigen. The regulatory activity of the autoreactive clones was assayed by co-cultivation with their target inducer clone. The autoreactive clones were not committed to a single program, they could either suppress or enhance the proliferation of the target cells depending on the state of activation of the target cells. Activated target cells were suppressed whereas non-activated cells were enhanced. It is predicted that antagonistic cytokines released from the autoreactive clones exert differential effects on the target clone.

Interactions between autologous T cell clones

A human CD4 clone (Mx9/9) using the V beta 8 receptor was used as antigen to generate autologous clones (termed anti-Mx9/9 clones) which proliferate in response to this clone, but not other autologous clones. This was used as an experimental model to explore the specific interactions between autologous T cells. Anti-HLA-DR monoclonal antibodies inhibited the response of the anti-Mx9/9 clones, suggesting that these clones recognize their target antigen in association with HLA-DR. Because of the specificity of the anti-Mx9/9 clones for the initiating clone (Mx9/9), but not any other autologous V beta 8- or V beta 8+ CD4 clones, the target antigen seems to be part of the T cell receptor, but not V beta 8 itself. However, the anti-Mx9/9 clones responded also to the autologous EBV line, and thus the target antigen is not known. The regulatory activity of the anti-Mx9/9 clones was assayed by coculture with their target clone. A variety of responses were seen, both inhibitory and stimulatory, which varied depending on the "conditions" of the T cell used. These results suggest that T cells interact in a complex network, perhaps as complex as the regulatory interactions between antibody molecules and B cells.

Type II collagen-specific human T cell lines established from healthy donors

Four type II collagen-specific T cell lines established from the peripheral blood of a healthy donor were studied in detail. These CD4+ T cell lines with an alpha/beta T cell receptor proliferated in response to native and denatured human and chicken type II collagen and human type I collagen, but not to human type IV collagen or other potentially arthritogenic antigens. The T cell response showed typical dose response characteristics, peaked between 30 and 48 h, was major histocompatibility complex class II restricted and not due to a mitogenic effect. Type II collagen-reactive T cells could hardly be detected in freshly isolated peripheral blood mononuclear cells from healthy donors, as revealed by limiting dilution analysis (frequency less than 1/100,000). By prestimulation in bulk cultures for 10 days, type II collagen-reactive T cells could be approximately 1000-fold enriched. However, in these limiting dilution cultures, collagen-reactive T cells could only be observed in a narrow window of cell concentrations, suggesting that type II collagen-reactive T cells may be controlled by suppressive mechanisms in healthy persons.