Primary cellular target responsible for dimethylnitrosamine-induced immunosuppression in the mouse

The present studies were undertaken to identify the cellular targets responsible for immunosuppression by dimethylnitrosamine (DMN). The in vitro antibody responses of splenocytes from B6C3F1 mice exposed to 6 mg/kg DMN for 7 days to the T cell-independent antigen dinitrophenyl-Ficoll and the T cell-dependent antigen sheep erythrocytes were used for separation and reconstitution studies. The antibody-forming cell response of spleen cells from DMN-treated mice to the T-independent and T-dependent antigens was suppressed by 72% and 61%, respectively, when compared to vehicle controls. Whole spleen suspensions were fractionated into nonadherent populations by plastic adherence and Sephadex G-10 depletion of macrophages. Adherent antigen-presenting cells were obtained by incubating spleen suspensions in culture wells and removing nonadherent cells after 3 h. By combining vehicle and DMN nonadherent and adherent populations it was demonstrated that the population most affected by DMN exposure in both the sheep erythrocyte and dinitrophenyl-Ficoll responses was the nonadherent population. The lack of T cell dependence of the dinitrophenyl-Ficoll response was verified by elimination of T cells from whole spleen suspensions by monoclonal anti-thy 1.2 antibody plus complement treatment. These results indicated the B cell from DMN-treated mice as the splenic cell type responsible for suppressed antibody-forming cell responses to dinitrophenyl-Ficoll. B cells, T cells (prepared by cytotoxic elimination of B cells using anti-immunoglobulins) and adherent antigen-presenting cells (macrophages) from vehicle- and DMN-treated mice were fractionated and recombined and immunized with sheep erythrocytes (requires B cell, T cell, and macrophage cooperation). While splenic macrophages from DMN-treated mice supported control responses, T-helper activity was slightly reduced and B cell function was especially impaired. The conclusion that T cell function was less suppressed was supported by control responses of DMN-treated mice to concanavalin A but reduced responsiveness to lipopolysaccharide under conditions of limiting cell densities. These studies indicate that the primary cellular target of DMN exposure resulting in suppressed antibody responses is the B lymphocyte.