A PREFORMED PYROGENIC FACTOR RELEASED BY LIPOPOLYSACCHARIDE-STIMULATED MACROPHAGES

THE aim of this study was to investigate the pyrogenic activity of fac tor(s) released by rat peritoneal macrophages following a brief stimul ation with LPS. The effect of this factor on the number of circulating leukocytes and serum Fe, Cu and Zn levels, was also evaluated. The po ssibility that the content of interleukin (IL)-1 beta, IL-6 and tumour necrosis fatter (TNF) In the supernatant could explain the observatio ns was investigated. Supernatant produced over a period of 1 h by peri toneal macrophages, following a 30 min incubation with LPS at 37 degre es C, was ultrafiltered through a 10 000 MW cut-off Amicon membrane, s terilized, and concentrated 2.5, 5, 10 and 20 times. The intravenous ( i.v.) injection of this supernatant induced a concentration-dependent fever in rats with a maximal response at 2 h. The pyrogenic activity w as produced by macrophages elicited with thioglycollate and by residen t cells. The supernatants also induced neutrophilia and reduction in F e and Zn 6 h after the injection. Absence of activity in boiled supern atants, or supernatants from macrophages incubated at 4 degrees C with LPS, indicates that LPS was not responsible for the activity. In vitr o treatment with indomethacin (Indo), dexamethasone (Dex), or cyclohex imide (Chx) did not modify the release of pyrogenic activity into the supernatant or its effects on the reduction in serum metal levels. Alt hough Chx abolished the production of mediator(s) inducing neutrophili a, and Dex reduced the induction of IL-1 beta, TNF and IL-6, injection of the highest concentration of these cytokines detected In the super natants did not induce fever. In vivo treatment with Dex, but not Indo , abolished the fever induced by the supernatant. These results sugges t that macrophages contain pre-formed pyrogenic mediator(s), not relat ed to IL-1 beta, IL-6 or TNF, that acts indirectly and independently o f prostaglandin. It also seems likely that the pyrogenic activity is r elated to the factor responsible for the reduction of serum Fe and Zn levels, but not the neutrophilia.