Histamine Blocks Interleukin 2 (IL-2) Gene Expression and Regulates IL-2 Receptor Expression

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Abstract
Histamine inhibited the roliferative response of human peripheral blood mononuclear cells (PBMCT to the T cell mitoFen Phytohema P (PHA-P) in a dose-dependent fashion. This inhibition was mePutiated via the H2 receptor since cimetidine, a known H2 antagonist, removed the inhibition, whereas the addition of the H1 antagonist Diphenhdramine did not. Inhibition occurred durin the inductive phase of the cell cycle, since histamine added 24 hours aBter PHA-P stimulation had no effect on subsequent T cell proliferation, and was attributable to inhibition of interleukin-2 (IL-2) gene expression. Both secreted IL-2 and messenger RNA coding for IL-2 were inhibited by histamine. In contrast, histamne exerted no inhibitory effect on the expression of cell surface receptors for IL-2 as determined by flow cytometry. Furthermore, histamine-treated cells retained full responsiveness to exogenously administered IL-2, which completely reversed the anti-proliferative effect of histamine. In some donors, histamine enhanced the ercentage of IL-2 receptor positive cells. Stimulated PBMC from AIDS KS patients as a group, displayed a lower ercentage of IL-2 receptor bearing cells, which was significantly increased gy the addition of histamine even at concentrations as low as 10−-6 M and peaking at 10−-3 M. These findings indicate that histamine exerts its anti-proliferative effects on T cells by inhibiting IL-2 production, via blockade of IL-2 gene expression. In addition, histamine seems to exert immunomodulating effects on IL-2 receptor expression, particularly in those individuals with AIDS-KS.