Antilymphocyte serum: studies of the specificity of the rosette-inhibiting antibody in rabbit anti-mouse ALS.

In an investigation into the characteristics of the rosette inhibiting antibody of antilymphocyte serum (ALS), rabbit anti mouse ALS were assayed for antibodies against lymphoid cells from the spleen, lymph nodes and thymus of Quackenbush (Q) mice, and against spleen cells from athymic nude mice. The lymphagglutinating and lymphocytotoxic titres were similar with both Q and nude cells, and the titres showed no significant correlation with skin graft survival times in mice receiving the corresponding ALS. A significant depletion of peripheral blood lymphocytes occurred in animals receiving both an immunosuppressive and a non immunosuppressive ALS, suggesting that the antibodies involved in this depletion are not significant in determining the immunosuppressive activity of ALS. In contrast, the rosette inhibition titres showed a significant correlation with graft survival times in the results obtained in tests using Q spleen, lymph node and thymus cells. No inhibition of rosette formation was obtained when using nude spleen cells. However, the numbers of spontaneous rosettes formed by both the mixed B and T cell populations from Q spleen were not significantly different from the numbers formed by the largely B cell population from nude spleen. These results confirm that the antibodies of ALS which are responsible for both the in vitro inhibition of spontaneous rosette function and the in vivo suppression of graft rejection are specifically directed against a T cell population, and it is suggested that the antibodies are related if not identical.