Highly infective multidrug-resistant strain interferes with macrophage apoptosis

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

Bangkok

Simposio; Pathogenesis and Control of Emerging Infections and Drug-Resistant Organisms; 2008

In the early 90’s, Argentina was declared by WHO and IUATLD as a “hot spot” for multidrug-resistant tuberculosis (MDR-TB). Muñiz (M) and 410 strains are both MDR strains belonging to the Haarlem lineage. M was isolated in a hospital outbreak while 410, despite its identical RFLP genotype (has a single additional band) didn’t spread to the community. Although both were epidemiological, bacteriological and genetically characterized, little is known about their interaction with immune cells. The ability to inhibit macrophage apoptosis by Mycobacterium tuberculosis has been proposed as a strategy to subvert host immunity, but controversy remains. The best characterized cell death programs are the extrinsic or death receptor apoptotic pathway and the intrinsic or mitochondrial pathway both ending in caspase3 activation, but alternative mechanisms have been proposed, such as caspase independent cell death, autophagy and pyroptosis. We have previously reported that heat-killed (hk) M strain induced lower levels of apoptosis and TNF-α than the reference strain H37Rv (Rv) in monocyte derived macrophages (MDM). Moreover, we have determined that while M interferes with Rv-induced apoptosis, 410 does not. The aim of this study was to characterize the pathways that might be involved in the inhibition of Rv-induced apoptosis by the M strain. TNF-α, through its binding to TNFR1, has been proposed as the main mediator of mycobacteria-induced apoptosis. However, exogenously added rTNF-α didn’t increase Minduced MDM apoptosis after a 5 hour stimulation (%Annexin V+: Rv=25.3±5%, M=8.9±1.3%; M+50ng/ml rTNF-α=8.6±2.0%; 1:10 MDM:Mtb ratio). The intrinsic pathway was evaluated in MDM pre-treated with the strains and afterwards apoptosis was induced with staurosporin (ST,0.5µM). We observed that M and 410 strains induced higher resistance to death than Rv (ST =31.0±0.4%, Rv+ST=26.6±4.6%, M+ST=19.1±4.4%, 410+ST=15.5±3.8%; Rv vs M/410: p