Total macrophages (marker CD68 (cluster of differentiation)) and M1 macrophages (detected by iNOS (inducible nitric oxide synthase) staining) were increased in the intestinal tissue of infants with NEC, and TNF-α (tumor necrosis factor-alpha) secreted by M1 macrophages was significantly increased but c-kit (receptor tyrosine kinase) expression was significantly decreased in NEC infants [29]. Here, NTRK1 is linked to necrotizing enterocolitis.