Regulation of the immune response in autoimmune NZB/NZW F1 mice. II. Age dependent release of suppressive factors from spleen cells.

Supressor cells in the spleens of overtly autoimmune NZB X NZW (B/W) mice, but not age matched normal strain mice, were shown to release a small, less than 20,000 Dalton factor which inhibited early events in the anti-SRBC PFC response and the mitogenic response. This splenic inhibitory factor (SIF) was (i) stable on heating (56 degrees, 30 min) and freezine (-70degrees); (ii) non-specific for antigen; (iii) absorbed and/or inactivated by target cells in young B/W spleen cell cultures and (iv) released gradually into the culture medium by metabolically active cells. SIF also blocked the T-cell replacing effect of allogeneic factor (TRF) in the anti-SRBC response. These observations suggest that SIF may lead to the immunodepressed state in overtly autoimmune B/W mice by preventing the activation or differentiation of lymphocytes responding to exogenous antigen.