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Six individual peptides of the major histocompatibility complex (MHC) class I molecule H-2Kb were synthesized. Intravenous injection of peptide 6 into mice prolonged the survival of Kb (BL/6 or B10.MBR) skin grafts on allogeneic R101 and B10.AKM mice, respectively. This was specific, as control skin grafts from Kk (B10.BR) or Kbt (DBA/2) donors, respectively, were rejected at the same time in both control and peptide-treated mice. The optimal doses for peptide 6, which is from the α2 domain, were defined. The test system was the inhibition of proliferation in vitro of naive lymph node cells by syngeneic mitomycin c-treated spleen cells from R101 mice preimmunized with irradiated stimulator splenocytes of Kb (BL/6) origin. Down-regulation was specific, as proliferation in response to third-party allogeneic stimulator Kk (B10.BR) splenocytes was not inhibited. Of the six peptides of H-2Kb tested, potent down-regulatory cells were induced by peptides 2 (α1 domain) and 5 and 6 (α2 domain). The greatest down-regulatory activity was obtained by giving peptide 2 to mice that had already been immunized against H-2Kb by injecting EL4 cells. Under the same conditions, injecting peptide 2 did not induce any cytotoxic T cells. In contrast, specific cytotoxic lymphocytes (CTL) were induced when cells from primed mice were incubated for 4 days with heated stimulator cells from BL/6 mice. The data suggest that peptides from MHC class I molecules activate precursors of down-regulatory T cells, but not of CTL, and this may explain their ability to prolong skin allograft survival. [ABSTRACT FROM AUTHOR]

For the inhibition of T-lymphocyte proliferation in mixed lymphocyte culture (MLC) by in vivo alloantigen-induced specific T-suppressor cells (Ts), the Ts and responder cells must have major histocompatibility complex (MHC) class II identity, either in I-C or in I-A+I-E. In the case of I-C, the molecule is on the surface of the Ts and not on the surface of the stimulator or responder cells. This lack of I-C on the responder cells occurs even after pre-activation by antigen. l-J on the Ts is unimportant in the present system, by blocking the Ts surface molecules with antibody, it was shown that the two Ts genetic restrictions were due to distinct Is subsets, hearing I-C in one case and I-A + I-E in the other. Pretreatment of the Ts with anti-I-C antibodies(without complement) did not prevent specific Is binding to the alloantigen, as shown by absorption on monolayers. However, it blocked the ability of the Ts to cause suppression and this could be reversed by removal of the antibody with pronase. The responder population, when pre-activated. could be fractionated by absorbing on monolayers of syngeneic Ts. Under these conditions, the cells sensitive to suppression adhered to the monolayer. while the non-adherent cell could not he suppressed. It is proposed that a receptor, to an Ia molecule (I-C or I-A + I-E) of the Ts, appears on the surface of the pre-activated responder T cell and that this is required for the genetically restricted interaction between the responder cell and the [ABSTRACT FROM AUTHOR]

Six synthetic peptides of the MHC class I molecule corresponding to individual H-2Kb participants in amino acid sequences of domains α1 (peptide 1 and 2) and α2 (peptides 3, 4, 5, 6) were selected. Kb-specific suppressor T cells (Ts) were induced in vivo in mice, then pretreated with a set of peptides and assayed by proliferation decrease in a three-cell lymphocyte culture (MLC). The effector function of Ts was abolished by the complex of the α2-domain peptides (but not by the α1-domain peptides) and decreased by particular peptides separately (4, 5, 6) of the α2-domain. Both α1- and α2-domain peptides, added in high concentration, decreased otherwise efficient enrichment of Ts during the absorption-elution procedure on the syngeneic macrophage (Mø) monolayers. A similar significant effect was observed using the purified Kb molecule (100 µg/ml) in the allogeneic Mø monolayer. Interaction between Ts receptors and some MHC peptides indicates in effector Ts activation in vivo by induction with peptides 5 and 6 of the α1- domain. The fine mechanisms of interaction between MHC class I molecule epitopes and T-cell receptors of each of the T-cell subsets separately are presently being studied. [ABSTRACT FROM AUTHOR]

The purpose of the present study was to investigate the role of adherent mononuclear cells (AMC) in generation of suppressor T lymphocytes (T-Lph) in one-way allogeneic mixed lymphocyte cultures (MLC). Alloantigen-specific cytotoxic T-Lph were generated in MLC predominantly in the presence of stimulator AMC, but not responder AMC. The presence of responder AMC and the absence of stimulator AMC were optimal conditions for generation of non-cytotoxic (through the whole duration of MLC) suppressor T-Lph. These CD4-CD8+ suppressor T-Lph were allononspeeific but autorestricted (with responders in test MLC). [ABSTRACT FROM AUTHOR]

The MC-resistant specific suppressor T cells that inhibit DNA synthesis and CTL generation in MLC were induced in vivo by γ-irradiated allogeneic lymphoid tells in a large dose. MLRs were inhibited only slightly when triggered by third-party cells, even neighbouring with the corresponding stimulators. Unlike the irradiated cells, intact allogeneic lymphoid cells induced a mixture of macrophage-like and T-cell suppressors with a pronounced non-specific component of the action. Syngeneic cells induced low active non-specific suppressors of macrophage type only. The suppression was not due to a cytotoxic effect, since specific T suppressors differed from CTL by conditions of induction and high sensitivity to γ-irradiation and from CTL precursors by high sensitivity to CY and HC. The specific T-suppressors could be selectively removed by adherence to a macrophage monolayer of the corresponding donor. The subsequent elution of adherent lymphocytes with pronase resulted in enrichment of specific T suppressors by a factor of 30 and 2.6, as judged by reduction in the number of lymphocytes required for 50% inhibition of DNA synthesis and 33% inhibition of CTL generation, respectively. The high specificity of this enrichment is shown by using both syngeneic monolayers for fractionation and third-party stimulators in MLR for testing and by disappearance of slight non-specific suppression caused by non-fractionated suppressors. Complete inactivation of the eluted suppressors with anti-Thy-1.2 and anti-T antibodies, their resistance to anti-MIs antibodies, carrageenin, and carbonyl iron, together with the data of autoradiographic study and total DNA synthesis in the population indicate that the eluted highly specific suppressors represent mainly DNA-synthesizing large and medium T lymphocytes. [ABSTRACT FROM AUTHOR]

Optimum conditions were selected for testing of direct and indirect H-2 reactive rosette-forming cells (RFC) with the use of sheep or mouse erythrocytes coated with soluble H-2 antigens. Rosette formation with mouse erythrocytes is shown to be an immunologically specific reaction and to be inhibited by the pretreatment of cells with the corresponding soluble H-2 antigen preparation. Rate of killer cell and RFC formation is different after primary and secondary immunization with an allogeneic tumor. Unlike killer cells, RFCs are inactivated without complement by rabbit antibodies against mouse γ-globulin (MGG). In contrast to killer cells, which are eliminated in the presence of complement by anti-0 antibodies but not by anti-plasma cell antigen (PC.1) and anti-MGG antibodies, direct RFCs are not inactivated by anti-θ but are eliminated partially by anti-MGG and anti-PC.1. The RFCs are shown to be concentrated in the low-density fractions of the discontinuous bovine serum albumin gradient, whereas cytotoxic lymphocytes are distributed less closely, being concentrated in the intermediate fraction, which does not differ morphologically from the initial cell suspension. Killer and rosette-forming cells reactive to the same H-2 antigens appear to be two non-overlapping populations of T and B cells, respectively, and no T-B cooperation is required for destruction of target cells. [ABSTRACT FROM AUTHOR]

Optimum conditions have been found for a specific quantitative absorption of mouse lymphocytes on to allogeneic target cells. Using this technique, it has been established that C3H anti-A lymphocytes immune to the specificities of a single H-2 sub-locus (D) were absorbed neither on cells bearing only some of the components of the immunizing complex (DBA/1 and I/St targets) nor on their mixture. Conversely, C57BL anti-A lyrnphocytes immune to the specificities of two H-2 sub-loci (D and K) reacted separately with each of the components on corresponding third-party targets (B10.D2(H-2d) and C3H (H-2k) as shown both by the direct cytotoxic effect and by the quantitative absorption technique. The results of absorption of these lymphocytes on mixtures of B10.D2 and CSH target cells used in various proportions indicate that C57BL anti-A lymphocytes represent a mixture of two 'polyvalent' populations in ratio of 1:3. This, together with the previous data indicates that 'committed' lymphocytes may be 'polyvalent' and that the initial recognition step of H-2 antigens may result from a direct contact between membranes of grafted cells and 'unprimed' host lymphocytes. Structural matching of the membrane antigenic complex and of normal and immune lymphocytes is suggested as a decisive factor of immunological recognition initiation in a transplantation context. [ABSTRACT FROM AUTHOR]