Primary in vitro cytotoxic response of NZB spleen cells to Qa-1b-associated antigenic determinants

We have shown that cytotoxic lymphocytes generated in primary cultures of NZB spleen cells with H-2-identical BALB/c or B10.D2 stimulator cells exhibit specificity for Qa-1b-associated antigenic determinants. This unidirectional cytotoxicity constitutes the initial demonstration of a primary in vitro response to antigens of the Qa-Tla system. Such responses do not require H-2 homology between effector and target cells in the assay system. In fact, when H-2Dd homologous target cells were employed there was little, if any, evidence for development of primary H-2-restricted responses to minor locus histocompatibility antigens or viral antigens. In view of the recently defined role of Qa-1+, Ly-1,2,3+ cells as regulators of antibody responses, and of the deficiency of such cells in NZB mice, the observation of hyperreactivity for determinants of this system may be relevant to the development of autoimmunity in these animals.

Qa-1-Associated Antigens

In this report we present evidence for the generation of H-2-nonrestricted cytotoxic T lymphocytes (CTL) specific for determinants encoded in the Qa-1 region of the 17th chromosome. B10.BR (Qa-1a) CTL primed in vivo and restimulated in vitro with H-2-identical AKR, C3H, or CBA (Qa-1b) splenocytes lysend Qa-1b targets, irrespective of their H-2 haplotypes. Immunizations in the reverse direction produced H-2-nonrestricted CTL that lysed Qa-1a but not Qa-1b targets. Mapping experiments with target cells from B6 congenic mice confirmed that the locus controlling these reactions lies in the Qa-1 region. Although it has been difficult to raise antisera against Qa-1b gene products, our cytotoxic data argue that the recognition of the products of the Qa-1 region is bidirectional.

Determinants encoded in the Qa-1 region, detected serologically or by CTL, were found on both T and B cell blasts. We also found that an antiserum against Qa-1a gene products specifically blocked the cell-mediated killing of Qa-1a targets, thus suggesting that CTL and antibodies bind products of the same genetic locus. Whether Qa-1 is a single locus or a complex of serologically and CTL-defined genes, the nonrestricted nature of anti-Qa-1 CTL suggests important functional and structural similarities between Qa-1 and the murine major histocompatibility complex.

Qa-1-Associated Antigens

The Qa-1b allele is assigned to strains whose peripheral lymphocytes are not lysed by a standard anti-Qa-1 serum. In order to investigate whether Qa-1b represents a single allele or several alleles that have been grouped together as “not a,” we studied the activity of cytotoxic T lymphocytes (CTL) specific for Qa-1b-associated antigens. Cold target inhibition experiments were performed to test the ability of various Qa-1b targets to inhibit the lysis of 51Cr-labeled B10 blasts by B10.BR anti-C3H and C57BR anti-AKR CTL. Qa-1a targets did not inhibit lysis relative to controls syngeneic with the CTL. In contrast, Qa-1b cold targets strongly inhibited the lysis of labeled B10 targets. We found no differences in inhibition among 16 Qa-1b strains representing six H-2 haplotypes and nine different backgrounds. These data indicate that all of these Qa-1b strains express the Qa-1 antigens shared by B10 and C3H or AKR, and thus suggest that Qa-1 is markedly less polymorphic than H-2.

Experiments were also performed to test the possibility that Qa-1-associated antigens are involved in the recognition of minor histocompatibility determinants. CTL were generated in secondary cultures between strains identical at Qa-1 and at H-2, but differing at minor histocompatibility loci. These CTL were tested for their ability to lyse targets bearing the minor histocompatibility antigens of the stimulators, and sharing either Qa region or H-2 antigens with the stimulators. In contrast with the well established role for H-2K and H-2D antigens in the recognition of conventional determinants, we found that in both Qa-1a and Qa-1b strain combinations, Qa region homology was neither necessary nor sufficient for minor locus-specific lysis.

H-2-Nonrestricted Cytotoxic Responses to an Antigen Encoded Telomeric to H-2D

Cytotoxic T lymphocytes (CTL) were generated in secondary in vitro cultures against H-2-identical allogeneic stimulators. In some strain combinations, such as C57BL/10 (B10) responding to C3H.SW, cytolysis was restricted to target cells bearing the H-2 antigens of the immunizing strain. However, B10.BR effectors sensitized to C3H, AKR, or CBA efficiently lysed targets of several H-2 haplotypes, including B10 targets congenic with the B10.BR responders. The activity of these CTL was totally abrogated by anti-Thy 1.2 plus complement. Lysis of 51Cr-labeled B10 targets by B10.BR anti-AKR CTL was inhibited by unlabeled B10 and AKR targets equally well, thus showing that the clones killing B10 are included in the AKR-specific clones. In addition, both B10 and B10.D2 stimulator cells were effective in the in vitro boosting of the B10.BR anti-AKR cytotoxic response. Mapping experiments using B10, B10.A, B10.A(2R), B10.A(5R), C57BL/6, and B6-Tlaa mice indicated that the locus relevant to these phenomena maps to the right of H-2D. Since both Con A and LPS blast targets were susceptible to the activity of the nonrestricted CTL, antigens encoded by this locus are not unique to the T or B cell lineage.

Regulation of alloantigen-induced cytotoxic responses by concanavalin A-activated lymphoid cells: suppression by antigen elimination

Spleen cells activated by concanavalin A (Con A) and subsequently irradiated with 1500 R were able to suppress the primary in vitro cytotoxic lymphocyte (CL) response of syngeneic splenocytes to H-2 disparate targets. Similarly activated and irradiated BALB/c (H-2d) splenocytes which were cultured with C57BL/6 (H-2b) stimulators for 24 hr developed cytotoxicity for H-2b, but not H-2d, tumor cell targets. This suggested that Con A-activated cells allogeneic to the stimulator might suppress the development of cytotoxic lymphocytes by eliminating antigen early in mixed leukocytes culture. This hypothesis was supported by the observation that suppression of primary cytotoxic responses was overridden by the use of greater numbers of stimulator cells. Moreover, Con A-activated (A X B)F1 lymphocytes suppressed the response of parent A to the H-2 disparate strain C to a much greater extent than they suppressed A-anti-B responses generated in such cultures. Addition of greater numbers of F1 suppressor cells did reveal a suppressive effect not readily explicable on a cytotoxic mechanism, in that modest but significant suppression of the A-anti-B response was observed. Thus, antigen elimination is a major, but not exclusive, mechanism in the suppression of CL responses by Con A-activated cells.

Regulation of Alloantigen-Induced Cytotoxic Responses by Concanavalin A-Activated Lymphoid Cells: Suppression by Antigen Elimination

Spleen cells activated by concanavalin A (Con A) and subsequently irradiated with 1500 R were able to suppress the primary in vitro cytotoxic lymphocyte (CL) response of syngeneic splenocytes to H-2 disparate targets. Similarly activated and irradiated BALB/c (H-2d) splenocytes which were cultured with C57BL/6 (H-2b) stimulators for 24 hr developed cytotoxicity for H-2b, but not H-2d, tumor cell targets. This suggested that Con A-activated cells allogeneic to the stimulator might suppress the development of cytotoxic lymphocytes by eliminating antigen early in mixed leukocyte culture. This hypothesis was supported by the observation that suppression of primary cytotoxic responses was overridden by the use of greater numbers of stimulator cells. Moreover, Con A-activated (A × B)F1 lymphocytes suppressed the response of parent A to the H-2 disparate strain C to a much greater extent than they suppressed A-anti-B responses generated in such cultures. Addition of greater numbers of F1 suppressor cells did reveal a suppressive effect not readily explicable on a cytotoxic mechanism, in that modest but significant suppression of the A-anti-B response was observed. Thus, antigen elimination is a major, but not exclusive, mechanism in the suppression of CL responses by Con A-activated cells.

Regulatory mechanisms in cell-mediated immune responses. V. H-2 homology requirements for the production of a minor locus-induced suppressor factor

A mixed leukocyte reaction suppressor factor is produced by spleen cells sensitized in vivo and restimulated in vitro across non-H-2 antigenic barriers. Cells capable of producing this factor appear in the spleens of minor locus-immunized animals later than in animals sensitized to major histocompatibility complex-encoded antigens. However, both H-2 and non H-2-induced factors suppress proliferative responses to any alloantigen. Splenocytes from animals immunized with H-2-identical, minor locus-disparate cells produce suppressor factor in vitro only when restimulated with cells sharing both H-2 and non-H-2 antigens with the in vivo stimulators.