The Control of Apoptotic Death in the Cells of GranulomatousInflammatory Lesions from Mice with Latent Tuberculous Infection in theEx Vivo Model

Abstract

Tuberculosis is a leading worldwide health problem. The latent, symptom-free stage of tuberculous infection is characterized by the formation of granulomas, specific aggregates of immune cells, predominantly macrophages, containing mycobacteria. The apoptotic death of macrophages containing mycobacteria is considered the main mechanism by which animals and human organisms oppose tuberculous infection and control its development. Previously, we have comparedMycobacterium-host cell relationships in individual granuloma cells from mice with latent tuberculous infection and cells from mouse bone marrow and peritoneal cultures infected with BCG vaccine in vitro and shown that increased death rates were revealed for macrophages heavily loaded with mycobacteria after acute BCG infection in vitro. While in ex vivo cultures granuloma macrophages with large numbers of BCG mycobacteria in them were still viable and had neither apoptotic nor necrotic morphology. Since different specific cellular responses to latent chronic and acute BCG infection in mouse cells were determined, the our aim was to analyze granulomas isolated from the lungs, spleens and bone marrow of Balb/c mice with latent BCG infection for the presence of inducers and markers of apoptotic cell death. In granuloma cells with increased levels of the inducer of apoptosis TNFα, proapoptotic proteins Вах and Ваd, death receptor Fas/ CD95 and scavenge receptor CD36, we did not observe P53 stabilization or caspase-3 activation in the cytoplasm or nuclei of macrophages and dendritic cells, irrespective of the presence or absence of acid-fast BCG mycobacteria in them. The survival receptor CD30 was detected on the cell membranes of only few granuloma macrophages. However, at later times of tuberculous infection in mice, virtually all macrophages and other granuloma cell types had considerable amounts of the antiapoptotic protein Bcl-2 in the cytoplasm and, probably, mitochondria, in contrast to macrophages from bone barrow cell cultures and peritoneal exudates infected with BCG mycobacteria in vitro. Preservation of mitochondrial ΔΨm during staining of living granuloma macrophages containing large amounts of the Bcl-2 protein was indicative of its involvement in maintaining the integrity of mitochondrial elements and the protection of granuloma cells from death, because in similar experiments the control macrophages that did not have any Bcl-2 protein in them had considerably reduced ΔΨm and exhibited morphological signs of apoptotic death. Taken together, our results suggest that the antiapoptotic protein Bcl-2 has been proposed to contribute to the viability of granulomas macrophages not only in ex vivo culture, but also in the animal organism when faced with mycobacterial, proinflammatory and proapoptotic factors operating in granulomatous inflammatory lesions at various times of latent tuberculous infection in mice.