Protein tyrosine kinase regulates Fas-mediated apoptosis in human BCG-infected monocytes

Apoptosis of monocytes/macrophages has emerged as a central regulatory even t in the defense against mycobacterial infections. The involvement of prote in tyrosine kinases (PTK) in Fas-mediated apoptosis in T cells is well esta blished, but the possible role of PTK in Fas-dependent death of human bacil lus Calmette-Guerin (BCG)-infected monocytes remains unclear. Here, we firs t examined the expression and function of Fas on BCG-infected human monocyt es by flow cytometry. The results demonstrated that BCG-infected monocytes expressed significant Fas protein levels. In addition, engagement of the Fa s antigen with its agonistic antibody (Ab) resulted in apoptosis of monocyt es, as monitored by DNA analysis and fluorescence-activated cell sorter (FA CS) analysis. The apoptotic action of Fas was suppressed significantly by g enistein, indicating a role for PTK in this death process. Consistent with this observation, herbimycin A and tyrphostin, two selective tyrosine kinas e inhibitors with different mechanisms of action, effectively inhibited Fas -mediated apoptosis of BCG-infectcd monocytes, as demonstrated by DNA conte nt analysis. Moreover, we confirmed the effect of genistein, herbimycin A, and tyrphostin by examining apoptosis with the terminal transferase dUTP ni ck end-labeling (TUNEL) assay. Collectively, these data demonstrate that Fa s-induced apoptosis may represent an important mechanism for eliminating BC G-activated human monocytes and that this apoptosis is due, at least in par t, to signaling via a PTK pathway.