Release of interleukin I and low-molecular-weight lymphocyte-activating factors by rat peritoneal macrophages and its enhancement by acute non-specific inflammatory processes.

Peritoneal macrophages harvested from rats undergoing an acute non-specific inflammatory reaction induced by an injection of calcium pyrophosphate (CaPP) into the pleural cavity released increased amounts of interleukin I (IL-I)-like material. Lymphocyte-activating factors were also found in ultrafiltrates of the macrophage supernatants below 10 kd and 5 kd. A similar pattern of activity was observed when lysates of the macrophages were tested. In addition pre-exposure of normal peritoneal macrophages to an acute pleural inflammatory exudate before supernatant production enhanced the release of lymphocyte-activating factors found both in the unfractionated supernatant and a sub-5-kd ultrafiltrate. Thus these results demonstrate that an acute inflammatory reaction, initiated by a non-antigenic stimulus is able to stimulate macrophages remote from the inflammatory site to produce a factor which behaves like IL-I in a standard IL-I assay. The presence of low-molecular-weight factors (less than 5 kd) with similar activity may suggest that degradation of IL-I has taken place to yield active fragments. Acute inflammatory exudate also augments release of these factors which may be important in the pathogenesis of inflammation.