Pathogen-induced apoptosis of macrophages: a common end for different pathogenic strategies

Microbe-macrophage interactions play a central role in the pathogenesis of many infections. Several bacterial pathogens induce apoptosis specifically in macrophages, but the mechanisms by which it occurs differ, and the resul ting pathology can take different courses. Macrophage death caused by Shige lla flexneri and Salmonella spp. has been shown to result in the release of pro-inflammatory cytokines. Conversely, Yersinia spp. induce apoptosis by suppressing the signalling pathways that lead to the production of tumour n ecrosis factor (TNF)-alpha, a cytokine essential for the control of this in fection. It is likely that there are a variety of reasons why macrophages a re particularly susceptible to pathogen-induced apoptosis. One reason may b e the expression of surface receptors that recognize highly conserved bacte rial components, such as lipopolysaccharide (LPS) and bacterial lipoprotein s (BLPs). These receptors have recently been shown to activate pro-apoptoti c signalling pathways. The roles of macrophage apoptosis in different disea se processes are discussed.