CD38 expression and functional activities are up-regulated by IFN-γ on human monocytes and monocytic cell lines

Human CD38, a surface molecule expressed by immature and activated T and B lymphocytes, has been characterized as a molecule transducing activation and proliferation signals, and intervening in adhesion to endothelium via its ligand CD31. CD38 is also a complex ectoenzyme featuring ADP-ribosyl cyclase/cyclic ADP-ribose hydrolase activities, leading to the synthesis and degradation of cADPR, a Ca⁺-mobilizing agent. We investigated the effects of monocyte-activating stimuli (IFN-γ, IL-2, LPS, TNF-α, and GM-CSF) on the expression and function of CD38, starting from the observation that human monocytes and the derived lines U937, THP-1, and Mono-Mac-6 bear the molecule on their surface. Our results indicate that IFN-γ is a strong up-modulator of CD38, and IL-2 increases its expression only modestly. LPS, TNF-α, and GM-CSF had no detectable effects. Treatment with IFN-γ produced a dose-and time-dependent up-regulation of CD38 in monocytes and monocytic lines, which was paralleled by increased ADP-ribosyl cyclase/cyclic ADP-ribose hydrolase activities. Furthermore, CD38 ligation by specific MoAb reduced the IFN-γ-dependent enhancement of monocyte-dynamic adhesion to endothelial monolayers. These findings identify IFN-γ as a modulator of monocytic CD38 expression and indicate that CD38 plays a specific role in the activation and adhesion processes performed by monocytes.