Proinflammatory cytokines in the course of Mycobacterium tuberculosis-induced apoptosis in monocytes/macrophages

Mycobacterium tuberculosis (MTB) can induce apoptosis in monocytes/macrophages both in vitro and in vivo, and this phenomenon is associated with mycobacterial survival. The present study addresses the possibility that apoptotic and inflammatory pathways could coexist through a caspase-1-mediated mechanism. In this context, a caspase-1 inhibitor (YVAD), but not caspase-3 (DEVD) or caspase-4 (LEVD) inhibitors, was able to strongly inhibit MTB-induced apoptosis. Moreover, caspase-1 activity was confirmed by the increased maturation of interleukin (IL)-1β. Of interest, IL-1β and tumor necrosis factor (TNF)-α were produced massively in the course of infection, and both were inhibited by YVAD pretreatment. To determine whether TNF-α was produced actively by apoptotic cells, the intracytoplasmatic cytokine content and apoptotic phenotype were analyzed at the single-cell level. Results showed a progressive increase of TNF-α production in annexin V-positive cells. These results indicate that MTB-induced apoptosis is associated with proinflammatory cytokine production.