The macrophage to epitheliod conversion in Mycobacterium tuberculosis infection is mediated by:
TNF alpha
IFN-g
IL-4
TGF-Beia
Ref: Robbins Pathologic Basis of Disease, 8th edition, Pg: 183Explanation:T Cell-Mediated (Type IV) HypersensitivityThe cell-mediated type of hypersensitivity is initiated by antigen-activated (sensitized T lymphocytes, including CD4+ and CD8+ Tcells.Tubercle bacilli colonizing the lungs are persistent or nondegradable antigensThe perivascular infiltrate is dominated by macrophages over a period of 2 or 3 weeks.The activated macrophages often undergo a morphologic transformation into epithelium-like cells and are then referred to as epithelioid cells.A microscopic aggregation of epithelioid cells, usually surrounded by a collar of lymphocytes, is referred to as a granuloma.This pattern of inflammation, called granulomatous inflammation is typically associated with strong T-cell activation with cytokine production.M. tuberculosis enters macrophages by endocytosis mediated by several macrophage receptors: mannose receptors bind lipoarabino- mannan. a glvcolipid in the bacterial cell wall, and complement receptors bind opsonized mycobacteria.M. tuberculosis organisms replicate within the phagosome by blocking fusion of the phagosome and lysosomeAbout 3 weeks after infection, a T-helper 1 (TH1) response is mounted that activates macrophages to become bactericidal.Differentiation of TH1 cells depends on IL-12, which is produced by antigen-presenting cells that have encountered the mycobacteria.Mature TH1 cells, both in lymph nodes and in the lung, produce IFN-g.INF-g is the critical mediator that enables macrophages to contain the M. tuberculosis infection.IFN-g stimulates formation of the phagolysosome in infected macrophages, exposing the bacteria to an inhospitable acidic environment.Macrophages activated by IFN-y differentiate into the "epithelioid histiocytes" that characterize the granulomatous response, and may fuse to form giant cells.Activated macrophages also secrete TNF. which promotes recruitment of more monocytes.
Cells and Tissues of Immune System