Which of the following statement is not true about mycobacterium tuberculosis infection
Ref Robbins 8/e p368; 9/e p371 Macrophage are primary cells infected by M tb Granulomatous inflammation is a distinctive pattern of chronic inflammation characterized by aggregates of acti- vated macrophages with scattered lymphocytes. Granulo- mas are characteristic of ceain specific pathologic states; consequently, recognition of the granulomatous pattern is impoant because of the limited number of conditions (some life-threatening) that cause it (Table 2-8). Granulo- mas can form under three settings: * With persistent T-cell responses to ceain microbes (such as Mycobacterium tuberculosis, T. pallidum, or fungi), in which T cell-derived cytokines are responsible for chronic macrophage activation. Tuberculosis is the proto- type of a granulomatous disease caused by infection and should always be excluded as the cause when granulomas are identified. * Granulomas may also develop in some immune- mediated inflammatory diseases, notably Crohn disease, which is one type of inflammatory bowel disease and an impoant cause of granulomatous inflammation in the United States. * They are also seen in a disease of unknown etiology called sarcoidosis, and they develop in response to rela- tively ine foreign bodies (e.g., suture or splinter), forming so-called foreign body granulomas. The formation of a granuloma effectively "walls off" the offending agent and is therefore a useful defense mechanism. However, granuloma formation does not always lead to eradication of the causal agent, which is frequently resistant to killing or degradation, and granulo- matous inflammation with subsequent fibrosis may even be the major cause of organ dysfunction in some diseases, such as tuberculosis.