Distribution of macrophage markers suggests that maturation occurs from an A1 to A3 sequence. FACS analysis of Mac-1, M-CSF-R, F4/80, and CD31 expression by A1, A2, and A3 cell subsets. Mac-1 expression remains constantly expressed in the 3 subsets, whereas differentiation marker (M-CSFR and F4/80) expression increases from A1 to A3. Reverse correlation is observed for the immature macrophage marker CD31, whose expression decreases from A1 to A3.