IL-17 mediates control of <i>Mtb</i> HN878 through CXCL13 induction, lymphoid follicle formation and macrophage activation.

<p>B6 and IL-17^−/− mice were aerosol infected with ∼100 cfu <i>Mtb</i> HN878 and lungs were harvested on D60 post-infection. Pulmonary histology was assessed on formalin-fixed, paraffin embedded lung sections that were stained with H&E (a). Arrows depict T cell perivascular cuffing. Serial sections from infected lungs were also processed for immunofluorescence using antibodies specific for CD3 and B220 (b) or iNOS and F4/80 (c), and stained for CXCL13 mRNA expression by in situ hybridization (d). 400× magnification for immunofluorescence images. Arrows within (d) indicate CXCL-13 mRNA expression. The average size of T cell perivascular cuffing (a) and B cell lymphoid follicles (b) was calculated using the morphometric tool of the Zeiss Axioplan microscope. The number of iNOS-expressing cells per field (c) was counted and shown. n = 5–9 mice per group. ***p≤0.005.