Enhanced in vitro cytotoxic anti H-2 responses in the presence of Ia antigens

Cytotoxic T lymphocytes generated across and I-Ab mutant difference are directed against a molecule bearing Ia antigens

The recently discovered B6.C-H-2bm12 (bm12) histocompatibility mutant bears a mutation of the I-A subregion of the H-2b haplotype. We have studied cytotoxic T lymphocytes (CTL) generated in secondary mixed lymphocyte culture (MLC) between the bm12 mutant and the strain of origin C57BL/6 (B6). In both directions, strong CTL responses were generated against lipopolysaccharide-stimulated, but not against concanavalin A-stimulated target cells. Studies of the specificity of the bm12 anti-B6 CTL response, using target cells from a panel of H-2 recombinants, showed that the CTL were directed against specificities of the I-Ab subregion. This conclusion was confirmed by the observation that the bm12 anti-B6 CTL could be specifically blocked by anti-Iab, but not by anti-Kb antisera. EL4 tumor cells, which express Kb and Db but not Iab antigens, were not lysed by the CTL. The combined data confirm that bm12 is an I-A subregion mutant and indicate that the I-A subregion antigens, recognized by antibody and those recognized by CTL, are probably present on the same molecules. The CTL effector cells generated in secondary MLC across the I-Ab mutant difference had the surface phenotype Lyt 1- 2+.

Split unresponsiveness to the trinitrophenyl determinant. I. Manoeuvers which suppress either humoral or cell-mediated immune responses

2,4,6-Trinitrobenzene sulfonic acid (TNBS) injected intravenously (i.v.) makes mice fully tolerant to the trinitrophenyl (TNP) determinant. Administration of in vitro TNP-labeled syngeneic erythrocytes or thymocytes renders mice unable to develop contact sensitivity to picryl chloride, while the humoral anti-TNP responses seem to be unaffected. The reverse was found after pretreatment of mice with TNP-labeled isologous IgG (MGG) since only anti-TNP antibody responses, but not contact sensitivity to picryl chloride, were significantly reduced. TNP-coupled macrophages given to animals suppressed both the cell-mediated and humoral responses, and this might be due to the presence on their surface of TNP-labeled cytophilic antibody. TNBS administered i.v. binds to circulating proteins and formed blood elements. Thus the split unresponsiveness affecting either humoral or cell-mediated compartments after the injection of TNP-MGG or of haptenated cells respectively, is presumably due to dissecting events which in vivo after the injection of TNBS, occur simultaneously. These results may be interpreted to indicate that split unresponsive states to TNP determinants are mediated two independent mechanisms which require different tolerogen presentations to be triggered.

Cellular requirements for the induction of cytotoxic T cells in vitro

The stimulator and accessory cell requirements for the induction of cytotoxic T cell responses to alloantigens in vitro are reviewed. The ability of lymphocytes to stimulate was acquired early in development and was found to be a property of both Ig+ and Ig- cells. The presence of Fc receptors, complement receptors or Ia antigens on lymphocytes did not confer superior stimulator capacity. In contrast to lymphocytes mature macrophages were poor stimulators. When resting lymphocytes were used as a source of stimulator cells there was an additional requirement for an adherent accessory cell population for the induction of cytotoxic T cells. The accessory cell population functioned whether syngeneic or allogeneic with the responder and was required for the induction rather than the maintenance of the response. It was further characterized as an Ig+, theta, FcR+/-, CR +/-, Ia- cell which was not a mature macrophage. Accessory cells could be replaced to some extent by supernatants from spleen cell cultures. A model for T cell induction is proposed where only cells which produce unique inductive stimuli are able to function as stimulator cells. Stimulator cells are defined as those cells capable of stimulating cytotoxic T cell precursors directly and independently. Stimulator capacity is suggested to be a function of activated cells only, thus lymphocytes only stimulate following activation by accessory cells. Cells lacking innate stimulator capacity but exhibiting Ia antigens are suggested to stimulate via an alternative means.

Generation of cytotoxic cells in absence of blastogenesis by mouse leukemic cells in mixed cultures

Primary virus-induced murine leukemias and transplantable leukemic cell lines, originally induced by virus, chemical or physical agents, failed to stimulate normal spleen cells differing at the H-2 complex or at Mls locus in the one-way mixed leukocyte culture. Lack of stimulation seems at least partially due to a nonspecific inhibitory effect since in a "three-party" culture system the leukemic cells interfered with the mixed leukocyte reaction (MLR) of normal allogeneic cells. Characterization of the leukemic cell populations used, according to their T or B cell origin, disclosed that in most cases T cell markers were present. Also, no Ia antigens were detected on leukemic cells. Furthermore, using a 51Cr release assay, leukemic cells could sensitize allogeneic normal lymphocytes to kill specifically normal as well as leukemic targets, even when no MLR was detected in parallel cultures.

Expression of Ia determinants on immunocompetent cells

The expression of Ia (immune response region-associated) antigens on the surface of lymphocyte subpopulations with defined immunological function has been investigated by negative selection of subpopulations with anti-Ia sera and complement. Ia determinants were found on both unprimed (IgM) and on primed (IgG) antibody-forming precursor cells. No Ia antigens were detected on the surface of helper T cells. In contrast, suppressor T cells were sensitive to treatment with anti-Ia sera and complement demonstrating the presence of Ia determinants on this T cell subpopulation.