<i>M. tb</i> H37Rv augments PD-1 expression in WT mice and enhances bacterial burden in PD-1^−/− mice compared to WT mice.

<p>Total splenocytes from WT mice infected with H37Rv were stained with anti-CD4, anti-CD8 and anti-PD-1 using fluorescently-labelled antibodies to determine the expression of PD-1 on T cell subsets by flow cytometry. A. PD-1 expression on CD4 and CD8 cells of infected and uninfected WT mice. Cells were gated on CD4⁺ and CD8⁺ T cells and analyzed for the % of cells expressing PD-1 on the gated population. The upper dot plots (top panels) show PD-1 expression for CD4 cells, and the lower dot plots (bottom panels) show PD-1 expression for CD8 cells. Data shown here is a representative experiment of three. B. Total PD-1 costimulatory molecule expression by CD4⁺ and CD8⁺ splenocytes (mean±STDEV) in uninfected and infected WT mice. PD-1 expression is significantly higher in both CD4⁺ (p = 0.01) and CD8⁺ (p = 0.03) splenocytes, as determined by two-tailed student's t test. Data shown here is a representative experiment of three. C. Gross pathology photographs of the lungs from infected WT and PD-1^−/− mice. PD-1^−/− mice have very distinct deformed and perforated lungs after <i>M. tb</i> infection. It appears that PD-1^−/− mice develops cavities in the lungs, which is very unique to these mice compared to WT mice. D. Histology of the lung tissue sections after 30 days of infection in WT and PD-1^−/− mice stained with both Haematoxylin & Eosin and Acid Fast dyes. WT mice show very well structured granulomas compared to PD-1^−/− mice, whereas PD-1^−/− mice had very large granulomas with perforated lungs (2× larger in size as shown in the figure). PD-1^−/− mice developed severe lesions in the lungs after 30 days of infection with H37Rv. E. Bacterial burden is significantly higher at day 75 in PD-1^−/− mice compared to WT in both spleen (p = 0.0001) and lungs (p = 0.03). Data shown here is a representative of two independent experiments. Each CFU experiment has been carried out in triplicates (3 mice per experiment).