Human phagosome processing of Mycobacterium tuberculosis antigens is modulated by interferon-γ and interleukin-10

Intracellular pathogens, such as Mycobacterium tuberculosis, reside in the phagosomes of macrophages where antigenic processing is initiated. Mycobacterial antigen-MHC class II complexes are formed within the phagosome and are then trafficked to the cell surface. Interferon-γ (IFN-γ) and interleukin-10 (IL-10) influence the outcome of M. tuberculosis infection; however, the role of these cytokines with regard to the formation of M. tuberculosis peptide-MHC-II complexes remains unknown. We analysed the kinetics and subcellular localization of M. tuberculosis peptide-MHC-II complexes in M. tuberculosis-infected human monocyte-derived macrophages (MDMs) using autologous M. tuberculosis-specific CD4(+) T cells. The MDMs were pre-treated with either IFN-γ or IL-10 and infected with M. tuberculosis. Cells were mechanically homogenized, separated on Percoll density gradients and manually fractionated. The fractions were incubated with autologous M. tuberculosis -specific CD4(+) T cells. Our results demonstrated that in MDMs pre-treated with IFN-γ, M. tuberculosis peptide-MHC-II complexes were detected early mainly in the phagosomal fractions, whereas in the absence of IFN-γ, the complexes were detected in the endosomal fractions. In MDMs pre-treated with IL-10, the M. tuberculosis peptide-MHC-II complexes were retained in the endosomal fractions, and these complexes were not detected in the plasma membrane fractions. The results of immunofluorescence microscopy demonstrated the presence of Ag85B associated with HLA-DR at the cell surface only in the IFN-γ-treated MDMs, suggesting that IFN-γ may accelerate M. tuberculosis antigen processing and presentation at the cell membrane, whereas IL-10 favours the trafficking of Ag85B to vesicles that do not contain LAMP-1. Therefore, IFN-γ and IL-10 play a role in the formation and trafficking of M. tuberculosis peptide-MHC-II complexes.