PRODUCTION OF AN EARLY RELEASE, M(R)-36,000 MONOKINE BY STIMULATED RAT MACROPHAGES

Supernatants from rat peritoneal macrophage cultures stimulated with b acterial products contain a M(r) 36,000 factor that protects immature cortical thymocytes from loss of viability over a 4-hr incubation peri od in vitro. This effect could not be produced with purified transform ing growth factor-beta or recombinant interleukin-6 (IL-6). Further, t he partially purified M(r) 36,000 fraction was inactive in bioassays f or IL-1 and tumour necrosis factor. Maximal production of the factor o ccurred 2 hr after the addition of 20 mug/ml of lipopolysaccharide, as assessed by the titre resulting in 100% protection of thymocytes in a viability assay. The detection of protective activity within 5 min af ter addition of the stimulant could be attributed to the release of in tracellular stores but protein synthesis was required to account for t he increasing titre up to peak levels. The titre fell rapidly after 2 hr so that activity could not be detected at 4 hr. This profile of rel ease was refractory to repeated stimulation with lipopolysaccharide. C onjoint addition of lipopolysaccharide and indomethacin, did, however, allow release in response to subsequent challenge. Related to this fi nding, prostaglandin E2 completely inhibited the release of protective activity.