Cellular Activation Induced by BCG Is a PTK-Dependent Event

Mycobacterial antigens including BCG stimulate human peripheral blood mononuclear cells resulting in cellular proliferation and the release of inflammatory cytokines such as TNF-α. However, the signal transduction mechanisms responsible for the BCG-induced cell activation are not completely understood. In this study, we investigated the role of PTK as a signal transduction pathway in BCG-induced cell activation, with the use of two PTK inhibitors (genistein and tyrphostin). Our results indicated that genistein significantly inhibited BCG-induced cell growth determined by thymidine uptake in a dose-dependent manner. BCG-induced TNF-α secretion was completely suppressed by genistein in a dose-dependent manner, producing 92% inhibition at a concentration of 50 μM.In addition, strong inhibition (81%) of BCG-induced TNF-α secretion was observed with tyrphostin (30 μM), another specific protein tyrosine kinase with a different mechanism of action. These inhibitory effects were not attributed to an alteration in cell viability as judged by trypan blue staining, and were not due to LPS contamination. On the other hand, monoclonal antibodies directed against HLA-DR and DQ inhibited the BCG-induced secretion of TNF-α. Taken together, these findings suggest that PTK may play an essential role in BCG-induced cellular activation.