Expression of CCR2 and VEGFR1 is required for monocyte migration into Mycobacterium tuberculosis-induced lung granulomas

Abstract Granulomas provide protection against Mycobacterium tuberculosis (Mtb) infection and dissemination but also contribute to long term pathogen survival in the host. Macrophages are the dominant cell type in mycobacterial granulomas, playing a central role in bacterial control. Most macrophages recruited to the lung during infection are derived from monocytes in the blood. Our lab has previously shown that continuous cell replacement is important in mycobacterial lesions and CCL2 and granuloma macrophage-produced VEGF-A are required for granuloma maintenance as blocking the action of these chemokines results in the reduction of granuloma size and number in BCG and Mtb infection. Here we show that expression of CCR2 and VEGFR1 by monocytes is required for the migration of these cells into Mtb-induced lung granulomas. Blockade of CCR2 and VEGFR1 with Propagermanium or SU5416, respectively, reduced monocyte migration toward granuloma cells in vitro or in vivo. A 1:1:1 mixture of color-coded WT, Flt1 fl/fl x LyzMCre and CCR2−/− BM-derived monocytes was adoptively transferred into C57BL/6J recipient mice. The ratio of transferred cells in the lungs, spleen, blood, and BM was measured 1 day and 10 days after transfer. By day 10, most of the transferred cells were present in the lung parenchyma. Loss of VEGFR1 on the transferred monocytes decreased monocyte migration to the lung parenchyma dramatically while homing of CCR2−/− cells was inhibited to every tested site. In the granulomatous lung the main source of VEGF-A is the macrophage. We are developing macrophage-targeted blockade of VEGF-A to reduce granulomatous pathology with the reduction of off-target effects.