Apoptosis Inhibition as a strategy of a prosperous Multi-Drug Resistant Mycobacterium tuberculosis strain to evade the immune response.

YOKOBORI N; LÓPEZ B; GEFFNER L; SCHIERLOH P; BALBOA L; ROMERO M; ALEMÁN M; RITACCO V; BARRERA L; DE LA BARRERA S; SASIAIN MC

Plovdiv, Bulgaria

Congreso; 29th Annual Congress of the European Society of Micobacteriology; 2008

European Society of Micobacteriology

Purpose of the study The multidrug resistant Mycobacterium tuberculosis strain M of the Haarlem 2 sublineage has prevailed over other multidrug resistant M. tuberculosis strains in Argentina since it started clonal expansion in the early ‘90s. We have previously observed that strain M induced less apoptosis than strain H37Rv in human monocyte-derived macrophages. This study was aimed to explore further the influence of strain M on macrophage extrinsic and intrinsic apoptotic pathways and on caspase3 activation, their common final effect. Methods Apoptosis was assessed on macrophages pulsed 5 hours with heat-killed bacilli employing Annexin V/PI assay in presence/absence of exogenously added apoptosis inducers/mediators: i) staurosporin (0.5ìM) as intrinsic pathway stimulator, ii) rTNF-á (50ng/ml) as major mediator of mycobacteria-induced apoptosis via the extrinsic pathway and iii) PDTC (50 ìM) as inhibitor of nuclear factor êB activation in response to TNF. Caspase3 activation was also measured. Results Upon stimulation with staurosporin, strain M induced less macrophage apoptosis than H37Rv (19.1±4.4% vs. 26.6±4.6%, p<0.01). Addition of rTNF-á did not improve the low apoptosis induced on macrophages by strain M (H37Rv=25.3±5%, M=8.9±1.3%; M+rTNF-á=8.6±2.0%). PDTC produced a similar apoptosis increase in macrophages pulsed with M as it did in macrophages pulsed with H37Rv. Strain M induced less activation of caspase3 than H37Rv (8.6±1.0% vs. 16.9±2.0%, p<0.05). Conclusions Strain M seems to inhibit apoptosis mainly by interfering with the intrinsic apoptotic pathway. Neither a deficit of TNF-á nor the activation of nuclear factor êB influences this interference. The success of strain M might be related to this ability to evade the immune response by preventing host cell apoptosis.