CD206+MHCII− Macrophages Present in the Neonatal but Not Adult Intestine Do Not Derive from LysM Monocytes and Are Decreased in Experimental Necrotizing Enterocolitis

Necrotizing enterocolitis (NEC) is an intestinal disease targeting premature infants. While not well understood, its pathogenesis involves an underdeveloped intestinal immune system. In the neonate, this system is primarily innate, with Cx3cr1+ intestinal macrophages (Mφ) being the predominant population. In the murine neonatal intestine, the Cx3cr1+ compartment contains embryonic self-renewing Mφ (Ly6C−CD64+MHCII+Tim4+) that are largely replaced by monocyte-derived-Mφ at weaning, while only a small population of Tim4+ cells persist in adults. However, how inflammation affects the neonatal intestinal Mφ compartment is not known. Using flow cytometry, we found the neonatal but not adult murine intestine to contain a population of Cx3cr1HiCD64HiMHCII− cells (30.62% ± 1.6 of Cx3cr1+ cells). 28.7% ± 1.8 of these cells express CD206, a known marker of embryonic origin in other tissues. While 34.4% ± 1.2 of total CD206+ cells expressed Tim4 in dam fed pups, it increased to 49.3% ± 0.51 p≤ 0.01 in pups exposed to experimental NEC for 24 hours. This CD206+Tim4+ subset was mainly MHCII+. When Cx3cr1-expressing cells were depleted (Cx3cr1-Cre CSFR1-DTR mice), all Cx3cr1-expressing cells were depleted, including CD206+MHCII−and+, but not Ly6C+ monocytes. In contrast, when LysM-Cre was used (LysM-Cre CSFR1-DTR mice), pups had decreased Ly6C+ monocytes but the CD206+MHCII−and+ populations were not depleted. These results were confirmed by immunofluorescent staining for CD206 and IBA-1. Thus, we conclude that neonatal intestinal CD206+MHCII−or+ cells do not derive from LysM+ monocytes. We speculate that CD206+MHCII− cells acquire MHCII during NEC thus decreasing the CD206+MHCII− pool. Supported by NIH DK116568 (IDP)