In situ demonstration of intraepithelial lymphocyte adhesion to villus microvessels of the small intestine

The recirculation of lymphocytes through the intestinal mucosa is important for specific immune defense, but the origin and differentiation of intraep ithelial lymphocytes (IEL) are not fully understood. The present study ther efore used intravital microscopy to investigate the migration of IEL to the villus mucosa and Peyer's patches of the small intestine. IEL were separat ed from inverted murine small intestine and mesenteric lymph node (MLN) T c ells were also isolated. The adhesion of fluorescence-labeled lymphocytes t o postcapillary venules (PCV) of Peyer's patches and arcade microvessels of small intestinal villi was observed after injection. In some experiments, the effect of antibodies against adhesion molecules on cell kinetics were i nvestigated. IEL time-dependently accumulated in villus microvessels of the small intestine, whereas few MLN cells did. Few IEL adhered to the PCV of Peyer's patches. IEL were shown to express alpha (E)beta (7)-integrin but n ot L-selectin. The accumulation of IEL in villus archade was significantly inhibited by antibody against beta (7)-integrin or mucosal addressin cell a dhesion molecules (MAdCAM)-1, but not by alpha (E)-integrin. The combined b locking of beta (7)-integrin and MAdCAM-1 further attenuated the sticking o f IEL in this area, although it did not entirely block the IEL adherence. T he adherence of CD4(+) or TCR alpha beta IEL to villus microvessels was sig nificantly greater than that of CD4(-) or TCR gamma delta IEL. It was demon strated in situ for the first time that IEL adhered selectively to the vill us microvessels of the small intestine partly via beta (7) and MAdCAM-1.