It has been documented that IRF5 mediates macrophage M1 polarization,26 and our previous report has suggested that M1 macrophages promote NEC.20 Immunofluorescence staining showed that the expression of a M1 macrophage marker, iNOS, was significantly induced and that iNOS was mostly colocalized with CD68 (Fig. 3a). The gene discussed is IRF5; the disease is necrotizing enterocolitis.