p53 expression in cultured blood human monocytes infected with mycobacterial strains

An upregulation of the cell-cycle associated proteins p53 and p21/Waf1/Cip1 induced by mycobacteria was previously reported. We aimed to evaluate the expression of such proteins in peripheral blood human monocyte cultures infected with strains of different mycobacterial pathogens.

The study relied on the immunocytochemical determination of p53, p21/Waf1/Cipl, bcl-2 and on the Tunel detection of apoptosis in monocytes populations cultured on four-welled chamber slides (10(6) cells/well) infected with Mycobacterium tuberculosis, M. bovis and M. avium for four consecutive days (mycobacterium/monocyte ratio 10:1). The results were expressed as mean values and SD of the percentages of stainings recorded in five fields per slide.

The statistical analysis with Fischer test demostrated that at most sampling times the p53 and p21/Waf1/Cip1 expression and the apoptosis index were significantly higher in M. tuberculosis infected cultures than in controls (p<0.05). The M. bovis related picture diverged from the previous one for a lower p53 expression (p<0.05) at all sampling times. The M. avium infected culture values did not diverge significantly from the controls.

The p53 and p21/Wafl/Cipl upregulation is compatible with both host defense strategies and pathogen strategies (safeguard of intracellular sanctuaries). The discrepancies among different cultures suggest a direct relationship between p53 activation and mycobacterial ability to enter host cells.