NOS2 and graft versus host disease: A similar dermal CD11b+, MHC class II+ macrophage population was identified in the skin of BLT GVHD mice (Figure 4A), which also displayed a mixed M1/M2 macrophage polarization phenotype with increased expression of Cox2, Nos2, Arg1 and Ym1 (Figure 4B and Information S1).