Recent studies identified an association between genetic variants in the lymphotoxin-α (LTα) gene and leprosy. To study the influence of LTα on the control of experimental leprosy, both low- and high-dose Mycobacterium leprae foot pad (FP) infections were evaluated in LTa-deficient chimeric (cLTα-/-) and control chimeric (cB6) mice. Cellular responses to low-dose infection in cLTα-/- mice were dramatically different, with reduced accumulation of CD4+ and CD8+ lymphocytes and macrophages and failure to form granulomas. Growth of M. leprae was contained for 6 months, but augmented late in infection. In contrast, tumor necrosis factor knockout and tumor necrosis factor receptor 1 knockout FPs exhibited extensive inflammatory infiltration with an increase in M. leprae growth throughout infection. Following high-dose infection, cB6 FP induration peaked at 4 weeks and was maintained for 12 weeks. Induration was not sustained in cLTα-/- FPs that contained few lymphocytes and no granulomas. There was a reduction in the expression levels of inflammatory cytokines, chemokines, and chemokine receptors, including nitric oxide synthase 2, vascular cell adhesion molecule, and intercellular cell adhesion molecule. Furthermore, cLTα-/- popliteal lymph nodes contained a higher proportion of naive CD44loCD62Lhi T cells than cB6 mice, suggestive of reduced T cell activation. Therefore, both LTa and tumor necrosis factor are essential for the regulation of the granuloma, but they have distinctive roles in the recruitment of lymphocytes and maintenance of the granulomatous response during chronic M. leprae infection.
ASJC Scopus subject areas
- Pathology and Forensic Medicine