Characterization of the target cell antigen in I region-mediated lympholysis

The cytotoxic T-cell response to Ia antigens: lack of correlation between the level of specific cytotoxicity obtained in primary mixed lymphocyte reaction and the frequency of specific cytotoxic T lymphocyte

We have investigated the cytotoxic response to allogeneic I-E and I-A antigens in bulk culture and limiting dilution experiments. A high degree of specific killing could be generated from unprimed T cells of I-E-negative strains upon stimulation with cells expressing I-E. In such conditions, cytotoxic T lymphocytes (CTL) were generated in the absence of a specific proliferative response. The frequency determinations by means of limiting dilution experiments showed that I-E-specific CTL precursors were much less frequent than the K and D specific precursors. The results suggest the existence of a population of I-E-specific CTL that failed to grow under conditions that allowed the growth of class I-specific CTL.

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+.

A two-signal mechanism for the induction of cytotoxic T lymphocytes

Depletion of adherent cells from stimulator and responder lymphocytes by a single filtration through nylon wool columns led to complete abrogation of the cytotoxic response to the stimulating alloantigen. Cytotoxic responses were restored by adding anti-Thy-1 + complement-greated normal peritoneal exudate cells (PEC) syngeneic or allogeneic to the responding population. Alternatively, the response could be reconstituted with costimulator, a lymphokine obtained by stimulation of spleen cells with concanavalin A. Costimulator was not itself cytotoxic and induced few or no cytotoxic T lymphocytes (CL) in the absence of stimulator cells. Costimulator was also more efficient than allogeneic PEC, which in turn were more efficient than syngeneic PEC, in reconstituting the cytotoxic response. The number of CL produced to the activating alloantigen was shown to increase with increasing concentration of costimulator. More interestingly, in the presence of a relatively high concentration of costimulator, CL were also activated to target cells that differ in H-2 haplotype from the stimulating alloantigen. Lysis of the third-party target cells could not be inhibited by cold targets syngeneic to the activating alloantigen. A clonal assay for cytotoxic precursors was used to confirm that CL for the activating alloantigen and CL for the third-party H-2 antigens were derived from different progenitors. Only about 37% of the cytotoxic clones produced were specific for the activating alloantigen. These observations are explained in terms of a two-signal model of CL activation.

Qed-1--a target for unrestricted killing by T cells

Two prototype target determinants for unrestricted killing by T cells are defined: Qed-1a, detected on B6.Tlaa targets by C3H/HeJ lymphocytes primed in vivo and restimulated in vitro by B10.BR spleen cells; and Qed-1b, detected on C57BL/6J lymphocytes by B10.BR anti-C3H/HeJ effector cells generated in the same manner. Other mouse strains can be typed for Qed-1 by the ability of their lymphocytes to inhibit one of these lytic reactions. Of 55 inbred strains, 52 expressed either Qed-1a or Qed-1b, which thus behaved as products of alleles of a single locus, Qed-1. The remaining three strains, all H-2r, did not compete against specific lysis of Qed-1a, but inhibited Qed-1b-specific lysis only in part; it is proposed that these strains carry a third allele or haploype, Qed-1c. The Qed-1 locus was mapped distal to Qa-2. Qed-1b was found on both normal and mitogen-activated lymphocytes and did not appear confined to any lymphoid subpopulation. Cytotoxic responses, not restricted by H-2 and specific for antigens controlled by the Tla region, could be induced in several combinations of H-2-identical strains differing at Qed-1. Cells of some strains, like B10.BR, NZB, and SWR, responded directly in culture, even without priming in vivo.