Phenotypic characterization of fifty surface markers expressed by human M1 and M2a macrophages cultured with different serums and in the presence or absence of polarizing cytokines

Macrophages are ubiquitously distributed throughout the various tissues of the body and perform many functions. These include inflammatory responses against pathogens by classically activated M1 macrophages and the regulation of wound healing and tissue remodeling by anti-inflammatory alternatively activated M2 macrophages. The responsibility for these pleiotropic functions lies in the expression of a myriad of surface receptors unique to a given subset. Much of what we know about the function of human macrophage subsets has been gleaned by studying in vitro generated macrophages, matured in the presence of GM-CSF or M-CSF, and polarized with different cytokines. Oftentimes, culture conditions (such as the type of serum used, the duration of the culture and the use of polarizing cytokines) vary between studies making direct comparisons difficult. Furthermore, overlap in surface marker expression can make it difficult to distinguish between the different macrophage subsets. We directly compared the expression of fifty different surface markers on M1 and M2a macrophages cultured in the presence of fetal bovine serum, human AB serum or serum free media and found that the type or presence of serum used affected the expression of several markers such as CD200R1 and CD32. Moreover, we compared the expression of these surface markers on polarized and unpolarized macrophages and determined that polarization was critical to the expression of several of these markers, such as CD38 and SLAM F7. The results of these studies should significantly expand our knowledge of the phenotypic differences between human M1 and M2a macrophages as well as demonstrate the importance of culture conditions in generating these phenotypes.