The formation of the granuloma in tuberculosis infection

The development of the granuloma and its subsequent degeneration and necrosis, is the hallmark of infection caused by Mycobacterium tuberculosis. These structures probably evolved as primitive particle responses, but in mammals they are facilitated by the emerging acquired immune response, in which cytokines and chemokines help control their formation and integrity. In this brief review we discuss the pathology of these lesions in the two most widely used animal models (mice and guinea pigs). In addition, we argue against the idea that there is a balance between host immunity and bacterial survival, and that the latter possess mechanisms that control this, as some currently believe, and moreover discuss newer information regarding the ability of bacilli to persist in these structures long enough to eventually escape and become retransmitted.