Stimulators of tumour necrosis factor production released by damaged erythrocytes

We sought to characterize factors released by sonicated human erythrocytes that stimulate peripheral blood mononuclear cells (PBMC) to release tumour necrosis factor-alpha (TNF). This response is not inhibited by polymyxin B, indicating that contaminating lipopolysaccharide (LPS) is not responsible. When erythrocyte lysates are fractionated by reverse-phase chromatography using a gradient of n-propanol on Sep-Pak C18 cartridges, the TNF-inducing activity elutes as a single peak. The erythrocyte-derived TNF-inducing activity is unaffected by digestion with proteases but is destroyed by mild base hydrolysis or digestion by lipases, indicating that compounds containing ester-linked acyl chains may be essential. These properties are similar to those of TNF stimulators that we have previously identified in erythrocytes infected with malaria parasites, except that the TNF-inducing activity per cell is about 200 times higher in parasitized erythrocytes than in uninfected erythrocytes. Lipase-digested erythrocyte lysates inhibit the TNF-inducing factors of both normal and malaria-infected erythrocytes, suggesting that lipase digestion creates partial structures which compete with active components for macrophage receptors. Such receptors may recognize a common structure that contains an inositol monophosphate (IMP)-like component, as IMP also inhibits the TNF response to erythrocyte-derived factors and to parasite lysates whereas it does not affect the response to LPS. We conclude that lysed erythrocytes release specific cytokine-inducing factors that may contribute to the fever response to non-infectious tissue injury.