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.
Highlights
The gene complex Antigen Presenting Lectin-like gene Complex (APLEC) (Antigen Presenting LEctin-like Complex) was first described by Flornes et al as a gene cluster located on rat chromosome 4, mouse chromosome 6 and human 12p13 [1]
BWZ cells virally-transduced with a chimeric protein consisting of the extracellular sequence of Macrophage C-type lectin (MCL), the transmembrane domain from killer cell lectin receptor H1 (KLRH1) and the cytoplasmic segment of the T-cell surface glycoprotein CD3 zeta chain were used for both immunization and screening as previously described [20]
We have shown that rat resident peritoneal macrophages in a steady state express MCL, and that this expression is increased when sterile peritonitis is provoked by zymosan
Summary
The gene complex APLEC (Antigen Presenting LEctin-like Complex) was first described by Flornes et al as a gene cluster located on rat chromosome 4, mouse chromosome 6 and human 12p13 [1]. MCL is a type II transmembrane protein with a single extracellular C-terminal C-type lectin-like domain. This domain contains an evolutionarily conserved folded domain, and a carbohydrate recognition domain containing the Ca2+ binding sites that give name to this family of proteins [2]. Its presence suggests a possible carbohydrate binding function, such receptors are known to recognize protein ligands. Two of the APLEC receptors; Dectin-2 (human) and Mincle (mouse), have been shown to recognize carbohydrate moieties from fungi, yeast, platyhelminthes, house dust mites and bacteria [3–8]. Their presence on the surface of immune cells and their potential for recognizing polysaccharide structures suggests a central role as pattern-recognition receptors in the innate immune system
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