Specific attachment of mesenteric IgA lymphoblasts to specialized endothelium of intestinal mucosa lamina propria capillaries.

The bulk of IgA secreted in the gut is mostly contributed by locally dwelling plasma cells derived from B cells originating in the gut-associated lymphoid tissues (GALT). These IgA cells originate in Peyer's patches and recirculate, returning to the gut upon maturity. The precise mechanism of homing to secretory mucosae is to date not fully understood. It has been demonstrated, however, that specialized endothelium of small vascular spaces in peripheral nodes (PN) and endothelia of mucosal vessels are the site of receptor recognition for B and T cells. In their sojourn, IgA blasts have been shown to stop momentarily in mesenteric nodes (MN) before proceeding to their final destination, the lamina propria (LP) of the gut mucosa. They then develop into IgA-secreting plasma cells. In the present work, we show that IgA MN lymphoblasts, when compared to PN lymphoblasts, attach preferentially to LP venule and capillary endothelium, The B-cell maturation in the mesenteric lymph nodes, where IgA is the sole membrane-bound immunoglobulin, allows attachment of most of these cells. Our work suggests that the site of exit of IgA cells from the circulation are these specialized lamina propria venules and capillaries.