Immunological regulation of epithelial function.

The objective of this presentation is to develop a hypothesis through a survey of pertinent literature rather than to review an established area of physiology. The focal point is the mucosa of the small intestine. The major thesis is that lamina propria cells regulate functions of epithelial cells. Support for this comes from studies of the "immunophysiological" interplay that goes on in the mucosa and that has been amply revealed through investigations of host-parasite interactions. Immunological reactions in several intestinal helminth infections affect epithelial cell differentiation and development as well as secretory, absorptive, and digestive activities. Epithelial cells may be influenced indirectly as bystander cells during immunologically mediated inflammation or directly through their recruitment as effector components in immune reactions. Immune responses, by convention, are thought to be mediated by nonepithelial cells. Therefore, involvement of epithelial cells in effecting immunity or in responding to immunologically elicited signals implies a regulatory role for lamina propria cells in epithelial function. Confirmation of the capacity of epithelial cells to respond to the command of other cells with "memory" capabilities would imply the existence of a sensitive, locally organized, and highly specific adaptive mechanism in the host.