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

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.

Bacillus Calmette-Guerin (BCG) and environmental mycobacteria divert Dendritic Cell functions interfering with the differentiation of precursors into competent APCs I monociti umani possono generare cellule dendritiche in base alla natura dei segnali provenienti dal loro microambiente. Abbiamo testato se l’infezione dei monociti con micobatteri quali il Bacillus Calmette-Guerin (BCG), o il Mycobacterium smegmatis, modulasse il differenziamento dei monociti in cellule dendritiche competenti. Abbiamo osservato che i monociti infettati con BCG differenziavano in cellule dendritiche con un peculiare fenotipo caratterizzato dall’assenza del CD1a sulla loro superficie e da up regolazione di molte molecole come il CD80, CD86 o l’MHC. Questa popolazione cellulare originata, era in grado produceva citochine pro-infiammatorie come il TNF-a, IL-1b, e IL-6 e grandi quantità di IL-10 ma non erano in grado di produrre l’IL-12. Le cellule dendritiche differenziate in tali condizioni stimolavano le cellule T allogeniche in maniera simile alle cellule dendritiche di controllo ma, in particolare, però, queste inducevano una risposta Th2 se messe in contatto con cellule naive derivate da cordone ombelicale. Le cellule dendritiche derivate da monociti infettati con Mycobacterium smegmatis differenziavano in cellule dendritiche con lo stesso fenotipo delle cellule dendritiche derivate da monociti infettati con BCG, ma con diversa capacita immunoregolatoria. La capacità del BCG e dei micobatteri ambientali di sovvertire il differenziamento dei precursori in cellule dendritiche immunocompetenti può spiegare uno dei meccanismi con i quali i micobatteri influenzano la risposta immunitaria dell’ospite.