Release of interleukin-1 (IL-1) and IL-1-like factors from rabbit macrophages with silica.

Oil-elicited rabbit macrophages stimulated by endotoxin were found to release increased amounts of interleukin 1 (IL-1) when incubated with silica. The assays used to determine the amount of IL-1 released were uptake of thymidine by mouse thymocytes, fever in rabbits, and neutrophilia in rats. All three assays showed that endotoxin-stimulated macrophages released five to 10 times more IL-1 when incubated with silica. Most of the IL-1 had a molecular weight (MW) of about 14,000 with a smaller amount at a MW of approximately 35,000. All of the neutrophilia-producing activity had an isoelectric point (pl) near 7. Thymocyte proliferation was promoted about equally by activities near pH 5 and 7. Fever was found not only at these two isoelectric points but also at a pl above 8 which had neither of the other two activities.