Functional aspects, phenotypic heterogeneity, and tissue immune response of macrophages in infectious diseases

de Sousa, Jorge Rodrigues; Da Costa Vasconcelos, Pedro Fernando; Quaresma, Juarez Antonio Simões

Macrophages are a population of cells that play critical roles in maintaining homeostasis and in the pathogenesis of inflammatory, infectious, and neoplastic diseases. 220 Macrophages are found in both blood and tissues, and despite their common origin in the bone marrow, tissue macrophages appear to exhibit an embryogenic development that is independent of that of blood macrophages or even of macrophages that migrate from the blood into tissues. [221] [222] [223] Macrophages perform a wide spectrum of functions in various tissues, including the removal of dead cells, as well as tissue remodeling and repair, which are associated with an elaborate response to foreign agents and infectious or noninfectious aggressors. [224] [225] [226] Given this, macrophages are crucial for the development of the organ-specific immune response, which acts on innate and adaptive immunity, frequently serving as a bridge between these two types of responses. 2, 227, 228 During an immune response, macrophages can function to maintain tissue homeostasis as well as contribute to the development of tissue lesions that are ultimately the result of a lack of control of the tissue immune response against aggressors. These aggressors concurrently trigger mechanisms to escape the action of macrophages, thus leading to a lack of control of the cellular response associated with tissue injury. [229] [230] [231] [232] [233] [234] This phenomenon is observed both in non-infectious and infectious diseases caused by viruses, bacteria, fungi, protozoa, and helminths.