Inhibition of primary antibody response in vitro by cancerous ascites

Acellular ascitic fluid from Ehrlich ascites carcinoma (EAC) was tested for its capacity to influence the development of plaque forming cells (PFC) responses in cultures of C5781 mouse splenic cells. 1.2 x 10⁷ dispersed single spleen cells were plated in Marbrook's vessels in 0.5 ml of fully supplemented RPMI 1640 medium, together with 0.05 ml suspension of sheep erythrocytes and 0.1 ml of acellular EAC ascites. Controls contained either 0.1 ml of medium or of ascites from mice injected i.p. with incomplete Freund's adjuvant. After 5 days incubation at 37°C in 5% CO₂, spleen cells cultured with EAC ascites produced far fewer PFC than did control cultures without ascites or with Freund's adjuvant ascites (150 vs 700 PFC/spleen). These data show that the immunodepressive activity of EAC ascites can be demonstrated in vitro. Previous failures to obtain similar results following in vivo administration of acellular EAC ascites could be due to the fast inactivation in, or the rapid elimination by the recipients's body of the immunodepressive ascitic factor(s).