Increased histidine decarboxylase expression during in vitro monocyte maturation; a possible role of endogenously synthesised histamine in monocyte/macrophage differentiation

Objective: In this study the expression of histidine decarboxylase (HDC), t he pivotal enzyme in histamine formation and the effect of endogenously pro duced histamine on differentiation antigens was examined during in vitro di fferentiation of human monocytes. Material and treatment., Human elutriated monocytes from healthy volunteers were incubated with macrophage colony stimulating factor (M-CSF) and the e xpression of HDC was followed at both mRNA and protein levels. To study the possible function of histamine we followed the expression of some cell sur face markers (CD14, CD16, CD91, CD49d and CD11c) relevant for phagocytic di fferentiation upon incubation in the presence of different histamine inhibi tors, an HDC inhibitor: S(+)-alpha -fluoromethyl-histidine HCl, (alpha FMH) , a compound that disturbs the interaction of histamine with intracellular cyp450 moieties: N,N-diethyl-2-[4-(phenyl-methyl) phenoxy]-ethanamine HCl. (DPPE); and H-1 and H-2 receptor antagonists, Triprolidine and Cimetidine. Results: During in vitro culture of elutriated human monocytes, in the pres ence of M-CSF, the gene expression and biosynthesis of HDC was considerably increased. The various antihistamine agents decreased th expression of the cell surface markers examined in this study. Conclusions:These data support the elevation of HDC expression during human monocytic differentiation and the possibility that monocyte-derived histam ine is partially involved in regulation of M-CSF induced in vitro human mon ocyte/macrophage phagocytic differentiation.