The Tuberculous Granuloma: An Unsuccessful Host Defence Mechanism Providing a Safety Shelter for the Bacteria?

Abstract

<jats:p>One of the main features of the immune response to<jats:italic>M. Tuberculosis</jats:italic>is the formation of an organized structure called granuloma. It consists mainly in the recruitment at the infectious stage of macrophages, highly differentiated cells such as multinucleated giant cells, epithelioid cells and Foamy cells, all these cells being surrounded by a rim of lymphocytes. Although in the first instance the granuloma acts to constrain the infection, some bacilli can actually survive inside these structures for a long time in a dormant state. For some reasons, which are still unclear, the bacilli will reactivate in 10% of the latently infected individuals, escape the granuloma and spread throughout the body, thus giving rise to clinical disease, and are finally disseminated throughout the environment. In this review we examine the process leading to the formation of the granulomatous structures and the different cell types that have been shown to be part of this inflammatory reaction. We also discuss the different<jats:italic>in vivo</jats:italic>and<jats:italic>in vitro</jats:italic>models available to study this fascinating immune structure.</jats:p>

Rv2744c Is a PspA Ortholog That Regulates Lipid Droplet Homeostasis and Nonreplicating Persistence in Mycobacterium tuberculosis

“…A hallmark of latent M. tuberculosis infection is the formation of host granulomatous lesions at sites of infection (10). Within the granuloma, M. tuberculosis is exposed to numerous environmental and/or biological "stressors" that alone, or in combination, are capable of damaging essential constituents of the bacterium.…”

A large pulmonary cavity replaced by a tuberculosis granuloma and healed during treatment of a patient with tuberculosis

“…The development of a caseous TB granuloma has been involved in the progression from latent TB to active disease and transmission, and caseation of human TB granulomas has been correlated with elevated host lipid metabolism in cells surrounding the caseum [9]. The network of factors that regulates the granulomatous inflammation and the host-pathogen interactions within the TB granuloma is complex and it is still unclear how a balanced response determines a protective rather than a destructive process [10,11]. Microarray profiling of caseous TB granulomas showed that many of the genes encoding enzymes involved in the lipid metabolism were differentially upregulated, and some of their encoded proteins were disproportionately abundant in cells surrounding the caseum.…”

Quiz. Correct answer to the quiz. Check your diagnosis Hodgkin’s lymphoma mimicking tuberculosis in cervical lymph nodes

“…Distinctively, in about 90% of cases superficial lymph nodes in the head and neck region are involved; rarely generalized lymphadenopathy and hepatosplenomegaly are described [13,14]. Major histological features are: chronic granulomas, predominantly with caseation necrosis, concentric layers of epithelioid cells, Langhans giant cells.…”