Figure 1. M. tuberculosis infection of guinea pigs results in progressive lung lesions that are less severe in BCG vaccinated animals. The lung lesion burden increases with time in guinea pigs infected by aerosol with the H37Rv strain of M. tuberculosis. BCG vaccination prior to challenge decreases the rate and severity of lung granulomas as determined by lesion scores. The bars represent median values plus range (when present) for each group (n = 5). The asterisks denote statistically significant increase compared to day 5 after infection (* = p,0.05, *** = p,0.001 and **** = p,0.0001). doi:10.1371/journal.pone.0034148.g001 restricted to a particular lesion type, tissue sections were scored as total or overall staining or were scored based on the extent of involvement of primary or secondary granulomas and uninvolved lung, designated primary lesion free lung (PLF). Overall immunostaining for OxLDL in lung sections from M. tuberculosis- infected guinea pigs increased gradually (Figure 3A) as the Oxidized LDL in the Guinea Pig Tuberculosis Model infection progressed and similar to the serum levels, correlated with disease progression (r = 0.99). The lungs from non-infected guinea pigs had minimal OxLDL accumulation in the normal lung parenchyma (Figure 3E). Statistically significant increases in OxLDL staining were seen on days 30 and 60 of the infection (p,0.01 for both) with the majority of the OxLDL staining being restricted to the primary granulomas (Figure 3B). There were no significant changes in the expression of OxLDL within the PLF lung. OxLDL expression was most prominent in lesion-associated macrophages including those with vacuolated cytoplasm (foam cells), airway epithelial cells, vascular endothelial cells and granulocytes within the inflammatory zone of the primary granulomas with minimal staining within the necrotic center (Figure 3E and F). Guinea pig lung cells collected by bronchoalveolar lavage also showed an increase in accumulation of cytoplasmic OxLDL by days 30 and 60 of infection (Figures 4A and B respectively). The BAL cells were predominantly alveolar macrophages intermixed with fewer numbers of granulocytes in which OxLDL expression levels were similar to that seen for macrophages. BAL cells from non-infected animals showed minimal to no OxLDL staining (data not shown). CD36 expression in lungs The scavenger receptor CD36 is a receptor for OxLDL and is expressed on a wide range of cell types including macrophages. With the progressive increase in OxLDL expression in the lungs of M. tuberculosis infected guinea pigs, we used immunohistochemistry to determine whether there was a corresponding increase in the OxLDL receptor CD36. Overall CD36 expression in the lungs from M. tuberculosis- infected guinea pigs increased gradually as the infection progressed (Figure 5A). The increase in receptor expression levels correlated (r = 0.99) with the increase in the lung Figure 2. Serum OxLDL levels increase in guinea pigs infected with M. tuberculosis infection. In guinea pigs sham-vaccinated with saline, serum OxLDL levels increased with the progression of disease as determined by a competitive ELISA. BCG vaccination of guinea pigs prior to virulent challenge abrogated the increase in serum OxLDL levels. Data is expressed as the mean values for each treatment group (n = 5). The asterisks denote statistically significant increase compared to the naive animals (* = p,0.05 and *** = p,0.001). doi:10.1371/journal.pone.0034148.g002 PLoS ONE | www.plosone.org 4 March 2012 | Volume 7 | Issue 3 | e34148