Flow cytometric analysis of lymphocyte populations in guinea pig blood and spleen. Ia antigen expression and the effects of immunosuppressive agents.

A panel of novel mouse monoclonal antibodies was used, in an indirect immunofluorescence procedure, to identify subsets of guinea pig lymphoid cells which were quantified by flow cytometric analysis. The staining characteristics of the antibodies were also examined by alkaline phosphatase-anti-alkaline phosphatase staining of cryostat sections of spleen and cytocentrifuge preparations of blood and spleen mononuclear cells. The values obtained for T and B cell populations were similar to those previously described using rosetting procedures, and the study also confirmed the high incidence of constitutive Ia antigen expression on guinea pig lymphocytes. Compared with animals receiving immunization (ovalbumin) alone, guinea pigs treated with ciclosporin A showed only minor changes in lymphocyte subsets, whereas those pretreated with cyclophosphamide revealed striking reductions in circulating T and B lymphocytes and in splenic B cells. Both ciclosporin A and cyclophosphamide markedly reduced Ia antigen expression on lymphocytes in blood, whilst cyclophosphamide also inhibited Ia antigen expression in the spleen.