Rat Macrophage C-Type Lectin Is an Activating Receptor Expressed by Phagocytic Cells

TLDR

Macrophage C‑type lectin (MCL) is a membrane receptor encoded by the APLEC gene complex. Using a mouse monoclonal antibody and the RMW myeloid cell line, the authors showed that MCL associates with the activating adaptor FcεRIγ and that antibody cross‑linking of MCL enhances phagocytosis. MCL is expressed on circulating monocytes, neutrophils, and various tissue macrophages, its expression rises with inflammatory stimuli, and it promotes phagocytosis in myeloid cells.

Abstract

Macrophage C-type lectin (MCL) is a membrane surface receptor encoded by the Antigen Presenting Lectin-like gene Complex (APLEC). We generated a mouse monoclonal antibody for the study of this receptor in the rat. We demonstrate that rat MCL is expressed on blood monocytes and neutrophils, as well as on several tissue macrophage populations, including alveolar and peritoneal cavity macrophages. We also demonstrate MCL expression on a subset of resident spleen macrophages. Immunohistochemistry analysis of the spleen showed staining specifically in the marginal zone and red pulp. Exposure to pro-inflammatory mediators or to yeast cell wall extract (zymosan) increased surface MCL expression on peritoneal macrophages. We characterized a rat myeloid cell line, RMW, which expresses high levels of MCL. We found that MCL co-immunoprecipitated with the activating adaptor protein FcεRIγ in these cells. Moreover, beads coated with anti-MCL antibody increased phagocytosis in the RMW cells. Together, these observations indicate that rat MCL is a receptor that activates phagocytosis in myeloid cells under inflammatory conditions.