Subversion of Macrophage Functions by Bacterial Protein Toxins and Effectors

Macrophages represent one of the first lines of host immune defenses against the invasion of pathogenic bacteria. Many receptors, immune signaling pathways and cellular processes in macrophages, including Toll-like receptors, Nod-like receptors, phagocytosis, autophagy and programmed cell death, are involved in combating the infection of bacterial pathogens. For efficient colonization in the host, bacterial pathogens have evolved diverse mechanisms to interfere with macrophage functions to evade host defenses. The major weapons utilized by bacterial pathogens are protein toxins and effectors secreted via specific bacterial secretion systems, including type I-VII secretion apparatuses. In recent years, great advances have been achieved in understanding how bacterial toxins and effectors subvert immune signaling and cellular processes of macrophages. In this review, we focus on the toxins and effectors that modulate the phagocytosis, intracellular immune signaling pathways, autophagy and programmed cell death processes of macrophages from the bacterium Legionella pneumophila, Shigella flexneri, Listeria monocytogenes, Salmonella spp., Yersinia spp., enteropathogenic E. coli and Mycobacterium tuberculosis.