Regulation of MerTK, GPNMB, and VSIG4 on mouse macrophages

We have developed flow cytometry antibodies against three molecules expressed on tissue-resident mouse macrophages: MerTK, GPNMB (aka Osteoactivin, DC-HIL), and VSIG4 (aka CRIg). MerTK, a receptor tyrosine kinase, plays a crucial role in the clearance of apoptotic cells, as well as in the regulation of cytokine secretion and survival. MerTK is highly expressed by splenic red pulp macrophages, which aid in the clearance of apoptotic cells in the blood. GPNMB, a transmembrane glycoprotein, plays a role in negatively regulating cytokine secretion during inflammatory responses and is expressed on tissue-resident macrophages, including microglia. Finally, VSIG4, a B7 family-related complement receptor, negatively regulates T cell-mediated responses and is also expressed on tissue-resident macrophages. The three clones DS5MMER (MerTK), CTSREVL (GPNMB), and NLA14 (VSIG4), were validated using resident and thioglycollate-elicited peritoneal exudate cells. DS5MMER (MerTK) and NLA14 (VSIG4) were also validated by IHC using frozen mouse tissue samples. Here, we have measured surface levels of MerTK, GPNMB, and VSIG4 on mouse bone marrow-derived macrophages by flow cytometry in response to an array of cytokines. We have also assessed the distribution of MerTK- and VSIG4-positive cells in various mouse tissues. Our data show how MerTK, GPNMB, and VSIG4 respond to various pro- and anti-inflammatory conditions in mouse bone marrow-derived macrophages and gives insight into how these receptors may be regulated on mouse macrophages in vivo.