RESUMO
AIM OF THE STUDY: Given that phagocytic cells are main players of the host immune response, we studied the interaction of bifidobacteria with monocytic THP-1 cells in nonopsonic conditions. METHODS AND RESULTS: Association/internalization, cell response (expression of HLA-DR and TLR2), M1/M2 macrophage polarization and colocalization of micro-organisms with Lysotracker or transferrin were evaluated. Screening with eight Bifidobacterium strains showed two patterns of interactions with THP-1 cells: high and low association and phagocytosis. Two strains with different surface properties were further studied: B. bifidum CIDCA 5310 and B. adolescentis CIDCA 5317. Strain CIDCA 5310 showed higher levels of colocalization in lysosome than strain CIDCA 5317. Both strains stimulated TLR2 expression. Strain CIDCA 5317 significantly increases HLA-DR expression, however, when cells are stimulated with IFN-γ, strain CIDCA 5310 induces the highest value of expression. Noteworthy, strain CIDCA 5310 was able to upregulate both M1 and M2 markers of macrophage polarization. CONCLUSIONS: Our results demonstrate that bifidobacteria from human origin show different patterns of interaction with phagocytic cells thus leading to different cell responses. These findings add further insight on the mechanisms involved in the biologic effects of probiotics. SIGNIFICANCE AND IMPACT OF THE STUDY: Knowledge of the interaction of bifidobacteria with key players of the host immune response is paramount for the understanding of the mechanisms involved in the beneficial effects.