Histamine inhibits tumor necrosis factor alpha release by mast cells through H2 and H3 receptors.

Histamine was one of the first inflammatory mediators thought to be important in the pathophysiology of asthma, but it is not now thought to be a mediator with primary importance in airway constriction. However, histamine has several effects that may be relevant. One of these effects, its immunoregulatory role, has been largely ignored in asthma. Thus, because mast cells (MC) are an important source of histamine and cytokines, the modulation by histamine of the release of one cytokine, tumor necrosis factor alpha (TNF alpha), was investigated. Rat peritoneal MC (PMC) were pretreated with different concentrations of histamine (10(-14) to 10(-4) M) for 2 h before being tested for their TNF alpha-dependent cytotoxicity. A concentration-dependent inhibition of cytotoxicity was observed from 21% at 10(-12) M to 38% at 10(-4) M, reaching a plateau at 10(-8) M. At least 1 h pretreatment with histamine or its presence throughout the cytotoxic assay was required for the inhibitory effect of histamine. This inhibition was abrogated by indomethacin or anti-PGE2, suggesting that PGE2 may be an important mediator in the inhibition of TNF alpha by histamine. To investigate the type of histamine receptor implicated in this effect, PMC were treated for 20 min with H1 (clemastine and diphenhydramine), H2 (ranitidine and cimetidine), or H3 (thioperamide) receptor antagonists before the addition of histamine. H2 or H3 antagonists abrogated the inhibitory effect of histamine on PMC TNF alpha-dependent cytotoxicity. Furthermore, blockage of H2 receptors with ranitidine increased the release of TNF alpha from PMC stimulated with antigen, suggesting that histamine released by MC within 10 min of antigen stimulation downregulates the subsequent release of TNF alpha from the same MC population. These results suggest that histamine may act as an autocrine regulator of cytokine release by MC and thus modulate inflammatory responses in allergic asthma.