Enterocyte‐lymphocyte interactions in the follicle‐associated epithelium of the mouse Peyer's patch.

1. Measurements of membrane potential (Vm) have been carried out in the follicle-associated epithelium of the mouse Peyer's patch to investigate possible site-dependent anomalies in enterocyte development. Initial heterogeneity in Vm values obtained from carrying out random impalements in the upper third of the follicle-associated epithelium could be described as arising from the presence of three different cell populations. 2. The predominant cell type in this epithelium (T1) had a mean Vm of -35.3 mV which was partly depolarized by increasing concentrations of K+. These cells were not stained with the vital dye Neutral Red. Two other types of cell (T2L and T2H) were recorded together as consecutive negative jumps in Vm, but only in areas of the epithelium previously stained with Neutral Red. T2L behaved like T1 cells to K+ but with a low Vm of -23.3 mV. T2H cells had a high mean Vm of -47.5 mV showing transient hyperpolarization to increasing K+ concentration. 3. The electrophysiological and non-staining properties of T1 cells are similar to those expected from mature enterocytes. The anatomical size, site, staining properties and Vm of T2H cells correspond to those expected for intraepithelial lymphocytes. The low Vm, K+ depolarization and close association of T2L with T2H cells are typical of properties predicted for an immature-type of antigen-transporting enterocyte known to be present in this type of epithelium. 4. The possibility that intraepithelial lymphocytes either slow or reverse a more normal process of development of enterocytes in their immediate vicinity is discussed along with wider aspects of enterocyte-lymphocyte interactions leading to the transfer to enteric antigens across these modified cells.