Mycobacterium tuberculosis targets DC-SIGN for immunosuppression through the PD-1/PD-Ligand pathway

The inhibitory axis of PD-1 expressed on T cells and its ligands produced by APCs mediates T cell exhaustion in chronic viral infection. We asked whether temporality of the infectious process is decisive for regulation through PD-1/PD-Ligand and investigated its impact on chronic bacterial infection. Here we show that M. tuberculosis and its lipid compounds induce expression of PD-Ligand on dendritic cells (DC). Upregulation of PD-Ligand depended on signaling through DC-SIGN upon infection. As a counterpart, expression of the PD-1 receptor was increased on T cells from tuberculosis patients and PPD+ donors compared to healthy normal individuals. Moreover, PD-1 expressing T cells were confined to granulomatous lesions in tuberculous lungs. Finally, functional blocking of PD-Ligand rescued antigen-specific T cell responses of tuberculosis patients. Taken together, we demonstrate that the inhibitory axis of PD-1/PD-Ligand is operative in mycobacterial infection and suggest inhibition of inhibition for rescuing exhausted T cells in tuberculosis. Keywords: Agilent two-color catolog 44K human whole genome microarrays Human PBMC-derived DCs were grown in 6-well plates and stimulated for 18 h with either mycobacterial ManLAM or recombinantly expressed ICAM-3. To ensure complete naïve status of DCs before stimulation, cells were left in wells from the day of PBMC isolation until end of stimulation. Change of medium was performed by carefully removing medium from wells without any manipulation of DCs. After stimulation, total RNA was isolated as described above and labeled with Fluorescent Direct Labeling Kit (Agilent Technologies) following manufacturer’s protocols. Microarray experiments were performed as two-color dye-reversal hybridizations. To compensate for dye-specific effects, a color swap was performed. Labeled RNA was hybridized on Whole Human Genome Oligo Microarray Kit 44k Format and scanned using an Agilent scanner according to manufacturer’s protocol (Agilent Technologies). Image analysis was performed using Feature Extractor software (Agilent Technologies). For data analysis Rosetta Resolver software was used (Rosetta Inpharmatics).