Abstract 41 Allergy and Immunology Platform, Monday, 5/3

There is considerable evidence that a subset of intestinal intraepithelial lymphocytes (IEL) develop extrathymically in mice, leading to the hypothesis that the intestine functions as a primary lymphoid organ. To gain insight into the phenotype and location of IEL precursors in the gut, we examined the small intestine of developing neonatal mice for colonization by T cell precursors and for the appearance of CD3+ IEL. We found that CD45+, CD3ε- cells were the majority of CD45+ cells isolated from the epithelium at 2 wks of postnatal age, while CD3ε+ IEL did not become a significant proportion until 3 weeks postnatal age and achieving adult numbers and proportions by 4 wks of age. While putative IEL progenitor cells exhibited some cell surface heterogeneity during neonatal to adult life, the majority of cells were CD44+ (80-88%), CD25lo/-, stem cell factor receptor, (CD117lo/-), while 30-40% of cells were Thy1+, suggesting that these cells were committed to the T cell lineage. Immunohistochemistry confirmed that CD3ε-, CD45+ cells were dispersed throughout the epithelium at 2 wks of age, but in addition, demonstrated subepithelial cell aggregates in the lamina propria. These aggregates were highly CD117+, with few cells expressing CD3ε, CD4 or CD8, consistent with recently described cryptopatch (CP) aggregates, probable sites of T cell development in the intestine. The ontogenic appearance of CP aggregates, CD3ε- cells and subsequently CD3ε+ IEL within the epithelium, suggests that CP aggregates give rise to CD3ε- intermediates present within the epithelium and that these pre-T cells complete their differentiation in the epithelium to become CD3ε+ IEL. Studies in normal and in select mutant adult and neonatal mice are underway to determine the sequence of differentiation events that T cell precursors take in the intra-intestinal development of TCR+ IEL.

Supported by grants from the NIH to the CHRC at University of Virginia and the Crohn's and Colitis Foundation of America Inc. (V.C.)