Possible role of histamine receptors in the central regulation of immune responses

The present study was designed to delineate the role of H1- and H2-histamine receptors in the neuro-immune regulation in rats. The effects of H1- and H2-receptor antagonists on humoral and cell-mediated immune (HI and CMI) responses were investigated after intraperitoneal (i.p.) and intra-cerebroventricular (i.c.v.) administration. HI response was assayed by anti-sheep red blood cell (SRBC) antibody titre in presence and absence of 2-mercaptoethanol (2-ME). The CMI responses were evaluated by delayed type hypersensitivity (DTH) reaction (in vivo), i.e., measurement of footpad thickness, and lymphokine activity such as leucocyte migration inhibition (LMI) test (in vitro). On i.p. administration, both H1- (pheniramine and astemizole) and H2-receptor antagonists (ranitidine and cimetidine) were observed to produce significant enhancement of anti-SRBC antibody response. However, only H2- and not H1-receptor blockers were observed to stimulate CMI response significantly. When administered by icv route, only H2-receptor antagonists caused a statistically significant increase in both HI and CMI responses, while the H1-receptor blockers failed to modify the same. Thus, H2-receptors appear to play a major role in the histaminergic mechanisms involved in immunomodulation both at the level of immunocompetent cells active in the peripheral tissues as well as through the central nervous system structures involved in the central regulation of neuro-immune interaction.