INFECTION

Monocytes differentiate into heterogeneous populations of tissue macrophages and DCs that regulate inflammation and immunity. Identifying specific populations of myeloid cells in vivo is problematic, however, because only a limited number of proteins have been used to assign cellular phenotype. Using mass spectrometry, we identified 106 plasma membrane protein markers of M-CSF-derived macrophages, classically and alternatively activated macrophages, and GM-CSF-derived DCs. In our own work, we used these markers to demonstrate that thioglycolate elicited peritoneal macrophages resemble GM-CSF-derived DCs, a result which we confirmed using genetic and functional approaches. In collaborative studies, we applied these surface markers to interrogate the phenotype of macrophages in atherosclerotic plaques, lymph nodes, and tumors.