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The Mycobacterium avium complex (MAC) is an important group of opportunistic pathogens for birds, cattle, swine, and immunosuppressed humans. Although invasion of epithelial cells lining the intestine is the chief point of entry for these organisms, little is known about the mechanisms by which members of the MAC are taken up by these cells. Studies with M. avium have shown that cytoskeletal rearrangement via activation of the small G-protein Cdc42 is involved and that this activation is regulated in part by the M. avium fadD2 gene. The fadD2 gene indirectly regulates a number of genes upon exposure to HEp-2 cells, including transcriptional regulators, membrane proteins, and secreted proteins. Overexpression of two fadD2-associated regulators (MAV_5138 and MAV_3679) led to increased invasion of HEp-2 cells, as well as altered expression of other genes. The protein product of one of the regulated genes, named CipA, has domains that resemble the PXXP motif of human Piccolo proteins, which bind SH3 domains in proteins involved in the scaffold complex formed during cytoskeletal rearrangement. Although CipA was not detected in the cytoplasm of HEp-2 cells exposed to M. avium, the recombinant protein was shown to be potentially expressed on the surface of Mycobacterium smegmatis incubated with HEp-2 cells and, possibly, to interact with human Cdc42. The interaction was then confirmed by showing that CipA activates Cdc42. These results suggest that members of the M. avium complex have a novel mechanism for activating cytoskeletal rearrangement, prompting uptake by host epithelial cells, and that this mechanism is regulated in part by fadD2, MAV_5138, and MAV_3679.

Many isolates of environmental mycobacteria (EM) isolated from fish and humans are examined for their abilities to grow in macrophage lines from humans, mice and carp. The studies have shown that understanding the role of the microbial genes in host specificity and pathogenicity is important for understanding the zoonotic potential of certain EM as well as their mechanisms of virulence.

Mycobacterium tuberculosis (Mtb) is transmitted via inhalation of aerosolized particles. While alveolar macrophages are thought to play a central role in the acquisition and control of this infection, Mtb also has ample opportunity to interact with the airway epithelium. In this regard, we have recently shown that the upper airways are enriched with a population of non-classical, MR1-restricted, Mtb-reactive CD8+ T cells (MAIT cells). Additionally, we have demonstrated that Mtb-infected epithelial cells lining the upper airways are capable of stimulating IFNγ production by MAIT cells. In this study, we demonstrate that airway epithelial cells efficiently stimulate IFNγ release by MAIT cells as well as HLA-B45 and HLA-E restricted T cell clones. Characterization of the intracellular localization of Mtb in epithelial cells indicates that the vacuole occupied by Mtb in epithelial cells is distinct from DC in that it acquires Rab7 molecules and does not retain markers of early endosomes such as Rab5. The Mtb vacuole is also heterogeneous as there is a varying degree of association with Lamp1 and HLA-I. Although the Mtb vacuole shares markers associated with the late endosome, it does not acidify, and the bacteria are able to replicate within the cell. This work demonstrates that Mtb infected lung epithelial cells are surprisingly efficient at stimulating IFNγ release by CD8+ T cells. [ABSTRACT FROM AUTHOR]

The article offers information about the ex vivo lung perfusion provides new insights into human lung-resident immune cell localization and functional interactions. It mentions that peripheral tissues have exposed to pathogens, requiring a specialized set of immune cells to recognize these threats. It discusses about tissue-resident memory considered as a player for protection from infection and cancer and participate in autoimmunity, allergy, and organ transplant rejection.

Processing and presentation of antigen on MHC-I class I molecules serves to present peptides derived from cytosolic proteins to CD8+ T cells. Infection with bacteria that remain in phagosomal compartments, such as Mycobacterium tuberculosis (Mtb), provides a challenge to this immune recognition as bacterial proteins are segregated from the cytosol. Previously we identified the Mtb phagosome itself as an organelle capable of loading MHC Class I molecules with Mtb antigens. Here, we find that the TAP transporter, responsible for importing peptides into the ER for loading in Class I molecules, is both present and functional in Mtb phagosomes. Furthermore, we describe a novel peptide reagent, representing the N-terminal domain of the bovine herpes virus UL49.5 protein, which is capable of specifically inhibiting the lumenal face of TAP. Together, these results provide insight into the mechanism by which peptides from intra-phagosomal pathogens are loaded onto Class I molecules. [ABSTRACT FROM AUTHOR]

The Mycobacterium avium complex (MAC) is an important group of opportunistic pathogens for birds, cattle, swine, and immunosuppressed humans. Although invasion of epithelial cells lining the intestine is the chief point of entry for these organisms, little is known about the mechanisms by which members of the MAC are taken up by these cells. Studies with M. avium have shown that cytoskeletal rearrangement via activation of the small G-protein Cdc42 is involved and that this activation is regulated in part by the M. avium fadD2 gene. The fadD2 gene indirectly regulates a number of genes upon exposure to HEp-2 cells, including transcriptional regulators, membrane proteins, and secreted proteins. Overexpression of two fadD2-associated regulators (MAV_5138 and MAV_3679) led to increased invasion of HEp-2 cells, as well as altered expression of other genes. The protein product of one of the regulated genes, named CipA, has domains that resemble the PXXP motif of human Piccolo proteins, which bind SH3 domains in proteins involved in the scaffold complex formed during cytoskeletal rearrangement. Although CipA was not detected in the cytoplasm of HEp-2 cells exposed to M. avium, the recombinant protein was shown to be potentially expressed on the surface of Mycobacterium smegmatis incubated with HEp-2 cells and, possibly, to interact with human Cdc42. The interaction was then confirmed by showing that CipA activates Cdc42. These results suggest that members of the M. avium complex have a novel mechanism for activating cytoskeletal rearrangement, prompting uptake by host epithelial cells, and that this mechanism is regulated in part by fadD2, MAV_5138, and MAV_3679. [ABSTRACT FROM AUTHOR]

Infection with Mycobacterium tuberculosis (Mtb), the bacterium that causes tuberculosis, remains a global health concern. Both classically and non-classically restricted cytotoxic CD8 + T cells are important to the control of Mtb infection. We and others have demonstrated that the non-classical MHC I molecule HLA-E can present pathogen-derived peptides to CD8 + T cells. In this manuscript, we identified the antigen recognized by an HLA-E-restricted CD8 + T cell clone isolated from an Mtb latently infected individual as a peptide from the Mtb protein, MPT32. Recognition by the CD8 + T cell clone required N-terminal O-linked mannosylation of MPT32 by a mannosyltransferase encoded by the Rv1002c gene. This is the first description of a post-translationally modified Mtb-derived protein antigen presented in the context of an HLA-E specific CD8 + T cell immune response. The identification of an immune response that targets a unique mycobacterial modification is novel and may have practical impact in the development of vaccines and diagnostics.