T cell subsets in the immune rejection of murine heterotopic corneal allografts

Using a previously described murine heterotopic corneal allograft model, we examined the roles of delayed-type hypersensitivity (DTH) and cytotoxic T lymphocytes (CTL) in corneal allograft rejection. We have previously shown that normal C57BL/6 mice consistently reject heterotopic corneal allografts within 14 days of grafting. These hosts develop antigen-specific CTL responses but no evidence of DTH reactivity. The absence of DTH suggested that this T cell subset was unnecessary for corneal allograft rejection. The present studies using T cell-deficient mice selectively reconstituted with specific T cell subsets confirmed this suspicion. T cell-deficient (i.e., adult thymectomized, lethally irradiated, bone marrow-reconstituted = ATXBM) C57BL/6 mice were selectively reconstituted with the following categories of syngeneic lymph node cells (LNC): (1) BALB/c skin-immune LNC treated with anti-Lyt 1 antibody + complement; (2) BALB/c skin- or cornea-immune LNC treated with anti-Lyt 2 antibody + complement; or (3) BALB/c cornea- or skin-immune LNC not treated with antibody. ATXBM mice reconstituted with syngeneic Lyt-1 depleted, BALB/c skin-immunized LNC failed to develop DTH, yet rapidly rejected BALB/c corneal allografts. Similarly, ATXBM mice reconstituted with Lyt 1-depleted cornea-immune LNC did not demonstrate DTH responses but were able to reject 100% of the corneal allografts in an accelerated fashion. By contrast, corneal allograft rejection was significantly delayed in ATXBM mice reconstituted with cornea-immune LNC partially depleted of Lyt 2⁺ T cells. Collectively, the results indicate that: (1) heterotopic corneal allografts can be rejected in the absence of DTH; (2) heterotopic corneal allografts fail to induce allospecific DTH; and (3) partial depletion of Lyt 2+ CTL leads to a prolongation of heterotopic corneal allograft survival. Thus, the primary T cell-dependent immune effector elements responsible for heterotopic corneal allograft rejection appears to reside in the cytolytic T lymphocyte population.