Mucosal dendritic cell subpopulations in the small intestine of newborn calves.

Mucosal dendritic cell development in the newborn is poorly understood despite evidence that distinct DC subpopulations populate individual mucosal surfaces. Therefore, we investigated DC phenotype and distribution in the small intestine of newborn calves. DC phenotype was analyzed using flow cytometry and DC distribution was investigated with immunohistochemistry. Purification of CD11c(Hi)MHC Class II(+) cells confirmed CD11c defined myeloid cells and a comparison of neonatal blood and intestine revealed distinct mucosal DC subpopulations. CD11c(Hi)CD14(+) cells were significantly more abundant in newborn ileum versus jejunum and CD335(+) NK cells were the only lymphoid population significantly different in ileum versus jejunum. Immunohistochemistry revealed unique patterns of myeloid cell distribution within the mucosal epithelium, lamina propria, and submucosa. CD11c(+) cells were present within the jejunal but absent from the ileal intraepithelial compartment. In contrast, CD11b(+) cells were present within the ileal but absent from the jejunal intraepithelial compartment. In conclusion, the neonatal small intestine is populated by diverse myeloid subpopulations and significant differences in regional distribution are established early in life. These observations may have significant implications for the response of the newborn to both commensal microflora and enteric pathogens.