The development of intraepithelial and Peyer's patch lymphocyte sub-types in the small intestine of newborn rats.

Small intestinal intraepithelial (IEL) and Peyer's patch (PPL) lymphocytes of newborn rats have been studied in histological sections and in isolated cell suspensions. Initially IEL numbers were low compared with older animals, and fewer cells were labelled by the monoclonal antibody markers used. At birth, 41% of IEL expressed receptors for MRC OX8 (T suppressor marker) yet lacked receptors for W3/13 (pan-T marker) which was present on only 1% of these cells. IEL with receptors for W3/25 (T helper marker) were not seen until 2 weeks of age. Granulated cells (GIEL) accounted for only 19% of IEL at birth. The numbers and relative proportions of these lymphocyte sub-types were still not mature at the time of weaning. In the first week of life there was a short lived upsurge in numbers of GIEL and MRC OX8+ IEL. The relative distribution of PPL sub-types was mature 4 weeks after birth, but the morphology of this tissue did not appear to be well differentiated until 1 week later.