Bacillus Calmette-Guerin (BCG) and environmental mycobacteria divert Dendritic Cell functions interfering with the differentiation of precursors into competent APCs

Thesis of PhD of Immunology 2004 Bacillus Calmette-Guerin (BCG) and environmental mycobacteria divert Dendritic Cell functions interfering with the differentiation of precursors into competent APCs Human monocytes can differentiate into dendritic cells (DCs) according to the nature of environmental signals. We tested here whether the infection with the live tuberculosis vaccine Bacillus Calmette-Guerin (BCG), that is known to be limited in preventing pulmonary tuberculosis, modulate monocytes and DCs differentiation. We found that monocytes infected with BCG differentiate into CD1a- DCs (BCG-DCs) in the presence of GM-CSF and IL-4 and acquired a mature phenotype in the absence of maturation stimuli. In addition, BCG-DCs produced pro-inflammatory cytokines (TNF-a, IL-1b, and IL-6) and IL-10 but not IL-12. BCG-DCs were able to stimulate allogeneic T lymphocytes to a similar degree as DCs generated in the absence of infection. However, BCG-DCs induced IL-4 production when co-cultured with human cord-blood mononuclear cells. Since environmental mycobacteria can interfere with BCG efficacy in preventing tuberculosis in some tropical areas, we verify whether this capacity to interfere with DCs functions was a feature common to environmental mycobacteria. To this aim, we infected DCs precursors with Mycobacterium smegmatis (Msm) to generate DCs. We found that Msm-infected monocytes differentiate into DCs with the same phenotype of BCG-DCs but some differences in the capacity to produce immunoregulatory cytokines and polarize naïve CD4+ T cells. The induction of IL-4 production by DCs generated from BCG-infected monocytes could explain one of the mechanisms for the failure of the BCG vaccine to prevent pulmonary tuberculosis.