Deciphering macrophage dynamics and immune evasion strategies by the intracellular bacteria.

Macrophages are the constituents of the innate immune system that play an important role in the control of infections, phagocytosis, tissue surveillance, and homeostasis. Macrophages display multiple strategies to cope with the invading microbes and prevent the spread of infections. On the other hand, many intracellular pathogens have evolved strategies to circumvent the macrophage-mediated immune responses and even thrive inside macrophages for their survival and replication. The intracellular bacteria possess a specific secretory system that secretes molecules that help regulate the host's immune responses. For example, Mycobacterium tuberculosis can successfully hide itself from the host immune system and replicate inside the host phagocytic cells with the help of chemicals secreted by its ESX secretion system. Therefore, it is necessary to deeply understand the interactions between macrophages and intracellular bacteria. This review gives insight into the biology of macrophages, inducers of antimicrobial responses in macrophages, and the secretory molecules of pathogens that aid in evading the host immune responses.