Granulomatous inflammation is which type of hypersensitivity? -: (A) Type I, (B) Type II, (C) Type III, (D) Type IV
Answer is D. Several autoimmune disorders, as well as pathologic reactions to environmental chemicals and persistent microbes, are now known to be caused by T cells . The occurrence and significance of T lymphocyte-mediated tissue injury have been increasingly appreciated as the methods for detecting and purifying T cells from patients' circulation and lesions have improved. This group of diseases is of great clinical interest because many of the new, rationally designed biologic therapies for immune-mediated inflammatory diseases have been developed to target abnormal T cell reactions. Two types of T cell reactions are capable of causing tissue injury and disease: (1) cytokine-mediated inflammation, in which the cytokines are produced mainly by CD4+ T cells, and (2) direct cell cytotoxicity, mediated by CD8+ T cells . In inflammation, exemplified by the delayed-type hypersensitivity (DTH) reaction, CD4+ T cells of the TH1 and TH17 subsets secrete cytokines, which recruit and activate other cells, especially macrophages, and these are the major effector cells of injury. In cell-mediated cytotoxicity, cytotoxic CD8+ T cells are responsible for tissue damage. Robbins 9 th edition page no. 118