The high-affinity IgE receptor (FcεRI) blocks apoptosis in normal human monocytes

Monocytes have a Limited life span, and their homeostasis is regulated by apoptosis in vivo. When cultured in the absence of appropriate exogenous stimuli, they undergo apoptosis, but under the influence of survival signals, these cells differentiate into macrophages or dendritic cells. Here we show that ligation of the high-affinity IgE receptor (Fc epsilon RI) on human monocytes from nonatopic individuals markedly reduces apoptosis induced by serum deprivation or by CD95/Fas ligation. Aggregation of Fc epsilon RI reduces its own expression but fails to modulate CD95/Fas expression. In contrast, Fc epsilon RI Ligation enhances the expression of the antiapoptotic molecules Bcl-2 and Bcl-xL, but not Mcl-1, in monocytes. Incubation of unstimulated cells with culture supernatants of Fc epsilon RI-activated monocytes prolongs their Life span, whereas CD95/Fas expression remains unaffected. The incidence of apoptosis is restored considerably when the supernatant is depleted of TNF-alpha, whereas elimination of IL-1 beta, GM-CSF, or IL-12 has no effect. These results indicate that Fc epsilon RI mediates signals preventing monocyte apoptosis directly by increasing the levels of Bcl-2 and Bcl-xL, and indirectly by means of TNF-alpha in an autocrine and paracrine fashion. This process may contribute to the establishment of chronic allergic disorders such as atopic dermatitis.