IL-22 enhances Calgranulin A expression by human macrophages to inhibit virulent <i>Mycobacterium tuberculosis</i> growth (158.21)

Abstract Previously, we found that IL-22 produced by NK cells inhibits intracellular mycobacterial growth in human macrophages (Mϕ) by enhancing phagolysosomal fusion. In the current study, we determined the mechanism/s by which IL-22 inhibits virulent M. tuberculosis H37Rv (M. tb) growth in Mϕ. First we asked whether IL-22 restricts M. tb growth in phagosomes that leads to enhanced phagolysosomal fusion. W7, a phagolysosomal fusion inhibitor abrogated IL-22 dependent M. tb growth in Mϕ (11.38 ± 3.3 x 106 vs 2.95 ± 1.7 x 106 CFU per well, p=0.05) suggesting IL-22 inhibits M. tb growth after phagolysosomal fusion. In microarray analysis we found that mRNA expression for 41 genes was >1-fold higher in rIL-22 cultured infected Mϕ compared to infected Mϕ. Of these genes, we selected Indolamine 2,3-dioxegenase (IDO1) and Calgranulin A for further study. rIL-22 enhanced Calgranulin A expression in M. tb infected Mϕ by three fold (3.3 ± 0.83 vs 1.0 arbitrary units, p=0.04) compared to infected Mϕ as measured by real time PCR and confirmed by confocal microscopy. In contrast, IDO1 expression of infected Mϕ was not effected by rIL-22. Calgranulin A siRNA abrogated rIL-22 dependent growth inhibition of M. tb in macrophages (18.4 ± 1.8 x 106 vs 7.97 ± 0.8 x 106 CFU per well, p=0.0005). Studies are underway to determine the effect of Calgranulin A siRNA on phagolysosomal fusion using early endosomal, late endosomal and lysosomal markers.