Mycobacterium tuberculosisTriggers Formation of Lymphoid Structure in Murine Lungs

Abstract

The hallmark of pulmonary tuberculosis is the granuloma, which consists predominantly of lymphocytes and macrophages and promotes immune-cell interaction with the causative pathogen, Mycobacterium tuberculosis. Granuloma formation is a highly organized process, which depends on leukocyte recruitment facilitated by adhesion molecules and chemokines. Thus, during chronic experimental tuberculosis, granulomata display characteristics of lymphoid structures comprising follicular aggregation of B cells, formation of high endothelial venules, presence of follicular dendritic cells, and expression of the homeostatic chemokines CXCL13 and CCL19. CCR7^−/−mice, which are deficient in CCL19 and CCL21 signaling, exhibit increased local inflammatory infiltrates but no follicular B-cell aggregation within those lymphoid structures. However, CCR7-deficient mice are fully capable to control pulmonary tuberculosis; at time points later than 6 weeks postinfection, they carry a lower bacterial load in peripheral organs. Our results show that, during chronic pulmonary tuberculosis in mice, the homeostatic chemokine signaling–network contributes to spatial organization of the granulomatous response, which participates in both containment of M. tuberculosis and the latter’s dissemination to other organs