Development of graft-vs.-host disease-like syndrome in cyclosporine- treated rats after syngeneic bone marrow transplantation. I. Development of cytotoxic T lymphocytes with apparent polyclonal anti-Ia specificity, including autoreactivity

were being recognized by the effector cells in animals exhibiting syngeneic GVHD. Table III summarizes the results of a representative experiment in which ACI and Lewis target cells were preincubated with a variety of mAb before being used as targets in a CML assay using effector cells from an animal with syngeneic GVHD syndrome. The results revealed that preincubation of Lewis and ACI target cells with the OX4 anti-Ia common determinant mAb resulted in significant reduction of lysis of the Lewis target cells. Preincubation of either the ACI or Lewis target cells with normal mouse serum, pan-T (W3/13) mAb or the anti-class I (OX18) antibody did not result in significant reduction of lysis. In three other experiments, identical results were observed with an average of 80% (+ 10% SE) reduction of lysis when the target cells were pretreated with Lewis and ACI blast cells labelled with 51Cr were incubated with normal mouse serum or mAb (0.1 ml of a 1:10 dilution per 106 cells) for 1 h at 4°C. The cells were washed twice in cold RPMI 1640 prior to use as targets in the CML assay. Nylon wool nonadberent spleens from an animal with the syngeneic GVHD syndrome were used as effector cells. Effector]target ratio was 75:1. * Percent specific SlCr release. * NT, not tested. the OX4 mAb. Spleen cells (nylon wool-nonadherent) from control transplanted animals tested against the mAb-pretreated targets did not result in significant lysis, apparently excluding Fc-mediated lysis. Treatment of YAC tumor cells with these antibodies did not reduce NK-specific lysis (data not shown). To confirm the presence of class II MHC antigens on activated rat T lymphocytes, cells were stained with anti-class II antibody, counterstained with fluoresceinated goat anti-mouse IgG, and analyzed on the fluorescence-activated cell sorter. Results showed that after PHA and Con A stimulation, ~30-40% of the rat T ]ymphoblasts express class II antigens.