Phenotypic comparison of ileal intraepithelial lymphocyte populations of suckling and weaned calves

Ileal intraepithelial lymphocyte (IEL) suspensions from suckling calves (1- 3 weeks old) and weaned calves (3-6 months old) were phenotyped to determin e whether there were differences in the lymphocyte populations consistent w ith postnatal maturation of the mucosal immune system. Flow cytometric comp arisons of IEL from the two age groups revealed the presence of significant ly larger proportions of CD4(+) T lymphocytes and CD8(+) T cells in the wea ned animals. In contrast, there was a significantly larger proportion of B- B2(+) IEL in the suckling calves. Freshly isolated IEL from both groups of calves expressed mRNA for TNF-alpha and IFN-gamma, but not IL-4 or IL-10. T he B-B2(+) IEL population was more closely examined by flow cytometry. Thes e cells co-expressed IgM and CD21. However, they did not express IgA, IgG1, nor any of several additional leukocyte differentiation molecules. Immunoh istochemical data confirmed the presence of IgM(+) lymphocytes, and the pau city of IgA(+) and IgG1(+) lymphocytes in suckling calf ileum. However, sub stantial numbers of IgA(+) and IgG1(+) cells were observed in weaned calf i leum. Together, the data are consistent with ongoing postnatal maturation o f the gut mucosal immune system. (C) 1999 Elsevier Science B.V. All rights reserved.