Macrophage plasticity and activation states drive differential expression of murine macrophage galactose-type lectin (MGL) orthologs

Abstract

Abstract Macrophage plasticity and functional activation are critical to the broad array of macrophage-mediated functions that help determine disease outcomes. Macrophage galactose-type lectin (MGL), a type-2 C-type lectin receptor (CLR) primarily expressed on myeloid cells, has been shown to play an anti-inflammatory role in the innate response to some infectious agents. Our lab recently demonstrated that MGL-1 contributes an antimicrobial and anti-inflammatory role in a murine model of experimental tuberculosis. We further observe that MGL-1 and MGL-2 expression by RAW 264.7 macrophages are similarly activated by whole mycobacteria, but differentially regulated by signaling through toll-like receptors (TLR) as well as cytokine and glucocorticoid receptors. We find that synthetic agonists and microbial ligands of TLR2, TLR4, and TLR7 positively regulate MGL-2 expression, suggesting responsiveness to a broad repertoire of antigens compared to MGL-1. Additionally, activation of MGL-2 expression differs between ligands of multiple bacterial species, both pathogenic and non-pathogenic. Pathway inhibition experiments show that MGL-2 upregulation by microbial stimuli occurs through MyD88-dependent Toll-like receptor (TLR) signaling. Although both MGL-1 and MGL-2 are classically associated with alternatively activated macrophages, we show that MGL-2 expression is associated with both M1 and M2 polarized macrophages, while MGL-1 expression is restricted to M2. These results demonstrate a strong relationship between macrophage activation states and the differential activation of MGL signaling and indicate non-redundant roles of MGL-1 and MGL-2 in innate immunity of murine models of disease. Supported by grants from NIH, NIAID (R61 AI138328, R33 AI138328)