In situ expression of CD40, CD40L (CD154), IL-12, TNF-alpha, IFN-gamma and TGF-beta1 in murine lungs during slowly progressive primary tuberculosis.

The distribution and expression of CD40, its ligand CD40L (154) and related cytokines interleukin-12 (IL-12), tumour necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma) and transforming growth factor-beta1 (TGF-beta1) were studied in the lungs of B6D2F1 hybrid mice during slowly progressive primary tuberculosis (TB) by immunohistochemistry. CD40 and CD40L are implicated in cell-mediated immunity (CMI) causing activation or apoptosis of infected cells. The phenomenon of apoptosis is associated with Mycobacterium tuberculosis survival. In this study, using frozen lung sections (n = 33), our results showed increased CD40, IL-12 and TGF-beta1 expression in macrophages with progression of disease. High percentages of mycobacterial antigens (M.Ags), CD40L and IFN-gamma expression were maintained throughout infection, and TNF-alpha-expressing cells were decreased. In lymphocytes, the percentage of IFN-gamma-positive cells was increased, but CD40L and IL-12 were maintained with the progression of disease. M.Ags, CD40 and CD40L were expressed in the same areas of the lesions. We conclude that changes in the expression of CD40-CD40L and cytokines associated with M. tuberculosis infection favour the hypothesis that M. tuberculosis causes resistance of host cells to apoptosis causing perpetuation of infection.

Increased Bcl-2 and reduced Bax expression in infected macrophages in slowly progressive primary murine Mycobacterium tuberculosis infection.

Mycobacterium tuberculosis (MTB) persists in host macrophages (Mphis) because it has developed mechanisms to escape Mphi killing. In vitro studies have shown that MTB can induce and inhibit apoptosis by causing the expression of Bax and Bcl-2, respectively, suggesting that the infected cells' fate depends on pro- and antiapoptotic signals. In the present study, we investigated the role of Bcl-2 in MTB infection in situ. The aim was to study the pattern and distribution of Bcl-2 and Bax in cellular infiltrates of MTB-infected B6D2F1 hybrid mice and correlate the expression with the presence of MTB antigens (MAgs). Using formalin-fixed lung tissues (n = 45), our results showed a significant difference in the percentage of Mphis stained for Bcl-2 or MAgs and Bax (P < 0.0001). Bcl-2 expression was increased in a population of Mphis and corresponded in intensity, colocalization and percentage with that of MAgs on the same cells, while Bax expression was reduced. In lymphocyte aggregates, Bcl-2 and Bax did not show any differences. We conclude that overexpression of Bcl-2 in Mphis containing MTB may be associated with intracellular survival of the bacilli, thus demonstrating one way by which MTB can escape the host's cellular response and killing.