The response of mouse peritoneal macrophages to Escherichia coli lipopolysaccharide (LPS) resulted in induction of histidine decarboxylase (HDC) and, consequently, of histamine production. Concanavalin A had no effect on the reactions. Alpha-fluoromethylhistidine, a suicide inhibitor of HDC, attenuated, in a dose-dependent manner, both spontaneous and LPS-stimulated IL-1 synthesis by macrophages. IL-1 production was significantly blocked by either an H1 anti-histamine, diphenhydramine, or H2 anti-histamine ranitidine, in the absence of any exogenous histamine. Addition of exogenous histamine accentuated the IL-1 production by macrophages as a function of its dose. These results suggest that IL-1 production by mouse peritoneal macrophages is regulated by histamine synthesized in the system per se and that the effect of histamine is dependent on both H1 and H2 histamine receptors located on the surface of the cells.
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