Levels of F4/80 and Ly6C correlate with M1, M2a, and M2c macrophage subtypes. Quantitative RT-PCR was used to evaluate mRNA expression of phenotypic markers from sorted macrophage populations isolated from muscles of 4-wk-old (A) or 8-wk-old (B) mice. Macrophage populations were defined and sorted (according to F4/80 and Ly6C levels) from a single sample of pooled muscles collected from six 4-wk-old mice (A) and six 8-wk-old mice (B). Samples were run in triplicate to measure the expression of these genes. All values are expressed relative to GAPDH. (C) Graph of M1 vs M2 ratios at 4 and 8 wk of age. Vertical lines represent SEM.