Biochemical and functional characterization of three activated macrophage populations

We generated three populations of macrophages (M phi) in vitro and characterized each. Classically activated M phi (Ca-3 phi) were primed with IFN-,y and stimulated with LPS. Type II-activated M phi (M phi-II) were similarly primed but stimulated with LPS plus immune complexes. Alternatively activated M phi (AA-M phi) were primed overnight with IL-4. Here, we present a side-byside comparison of the three cell types. We focus primarily on differences between M phi-II and AA-M phi, as both have been classified as M2 M phi, distinct from Ca-M phi. We show that M phi-II more closely resemble Ca-M phi than they are to AA-M phi. M phi-II and Ca-M phi, but not AA-M phi, produce high levels of NO and have low arginase activity. AA-M phi express FIZZ1, whereas neither M phi-II nor Ca-M phi do. M phi-II and Ca-M phi express relatively high levels of CD86, whereas AA-M phi are virtually devoid of this costimulatory molecule. Ca-M phi and M phi-II are efficient APC, whereas AA-M phi fail to stimulate efficient T cell proliferation. The differences between Ca-M phi and M phi-II are more subtle. Ca-M phi produce IL-12 and give rise to Th1 cells, whereas M phi-II produce high levels of IL-10 and thus, give rise to Th2 cells secreting IL-4 and IL-10. M phi-II express two markers that may be used to identify them in tissue. These are sphingosine kinase-1 and LIGHT (TNF superfamily 14). Thus, Ca-M phi, M phi-II, and AA-M phi represent three populations of cells with different biological functions.