title: Molecular and cellular mechanisms of Mycobacterium avium-induced thymic atrophy.
abstract: Thymic atrophy has been described as a consequence of infection by several pathogens and shown to be induced through diverse mechanisms. Using the mouse model of Mycobacterium avium infection, we show in this study that the production of NO from IFN-γ-activated macrophages plays a major role in mycobacterial infection-induced thymic atrophy. Our results show that disseminated infection with a highly virulent strain of M. avium, but not with a low-virulence strain, led to a progressive thymic atrophy. Thymic involution was prevented in genetically manipulated mice unable to produce IFN-γ or the inducible NO synthase. In addition, mice with a selective impairment of IFN-γ signaling in macrophages were similarly protected from infection-induced thymic atrophy. A slight increase in the concentration of corticosterone was found in mice infected with the highly virulent strain, and thymocytes presented an increased susceptibility to dexamethasone-induced death during disseminated infection. The administration of an antagonist of glucocorticoid receptors partially reverted the infection-induced thymic atrophy. We observed a reduction in all thymocyte populations analyzed, including the earliest thymic precursors, suggesting a defect during thymic colonization by T cell precursors and/or during the differentiation of these cells in the bone marrow in addition to local demise of thymic cells. Our data suggest a complex picture underlying thymic atrophy during infection by M. avium with the participation of locally produced NO, endogenous corticosteroid activity, and reduced bone marrow seeding.
authors.affiliation: Institute for Molecular and Cell Biology, University of Porto, 4150-180 Porto, Portugal.
authors.forename: Margarida
authors.initials: M
authors.lastname: Borges
authors.forename: Palmira
authors.initials: P
authors.lastname: Barreira-Silva
authors.forename: Manuela
authors.initials: M
authors.lastname: Flórido
authors.forename: Michael B
authors.initials: MB
authors.lastname: Jordan
authors.forename: Margarida
authors.initials: M
authors.lastname: Correia-Neves
authors.forename: Rui
authors.initials: R
authors.lastname: Appelberg
mesh_terms: D000818:Animals; D017209:Apoptosis; D001284:Atrophy; D002454:Cell Differentiation / Q000276:immunology; D005260:Female; D007371:Interferon-gamma / Q000502:physiology; D008262:Macrophage Activation / Q000276:immunology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D009162:Mycobacterium avium / Q000276:immunology* / Q000472:pathogenicity*; D052247:Nitric Oxide Synthase Type II / Q000172:deficiency / Q000235:genetics; D016176:T-Lymphocyte Subsets / Q000276:immunology / Q000382:microbiology / Q000473:pathology; D013950:Thymus Gland / Q000276:immunology* / Q000382:microbiology / Q000473:pathology*; D014774:Virulence / Q000276:immunology
chemical_list: D007371:Interferon-gamma; D052247:Nitric Oxide Synthase Type II