IFN-αβ Released by Mycobacterium tuberculosis-Infected Human Dendritic Cells Induces the Expression of CXCL10: Selective Recruitment of NK and Activated T Cells

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Abstract
We recently reported that dendritic cells (DC) infected with Mycobacterium tuberculosis (Mtb) produce Th1/IFN-γ-inducing cytokines, IFN-αβ and IL-12. In the present article, we show that maturing Mtb-infected DC express high levels of CCR7 and they become responsive to its ligand CCL21. Conversely, CCR5 expression was rapidly lost from the cell surface following Mtb infection. High levels of CCL3 and CCL4 were produced within 8 h after infection, which is likely to account for the observed CCR5 down-modulation on Mtb-infected DC. In addition, Mtb infection stimulated the secretion of CXCL9 and CXCL10. Interestingly, the synthesis of CXCL10 was mainly dependent on the Mtb-induced production of IFN-αβ. Indeed, IFN-αβ neutralization down-regulated CXCL10 expression, whereas the expression of CXCL9 appeared to be unaffected. The chemotactic activity of the Mtb-infected DC supernatants was evaluated by migration assays using activated NK, CD4+, and CD8+ cells that expressed both CCR5 and CXCR3. Mtb-induced expression of CCL3, CCL4, CXCL9, and CXCL10 was involved in the stimulation of NK and T cell migration. In accordance with the data on the IFN-αβ-induced expression of CXCL10, neutralization of IFN-αβ significantly reduced the chemotactic activity of the supernatant from Mtb-infected DC. This indicates that IFN-αβ may modulate the immune response through the expression of CXCL10, which along with CXCL9, CCL3, and CCL4 participates in the recruitment and selective homing of activated/effector cells, which are known to accumulate at the site of Mtb infection and take part in the formation of the granulomas.