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 intraepithelial lymphocytes (IEL) are not fully understood. The present study therefore used intravital microscopy to investigate the migration of IEL to the villus mucosa and Peyer's patches of the small intestine. IEL were separated from inverted murine small intestine and mesenteric lymph node (MLN) T cells were also isolated. The adhesion of fluorescence-labeled lymphocytes to 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 investigated. 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 α_Eβ₇-integrin but not L-selectin. The accumulation of IEL in villus archade was significantly inhibited by antibody against β₇-integrin or mucosal addressin cell adhesion molecules (MAdCAM)-1, but not by α_E-integrin. The combined blocking of β₇-integrin and MAdCAM-1 further attenuated the sticking of IEL in this area, although it did not entirely block the IEL adherence. The adherence of CD4⁺ or TCRαβ IEL to villus microvessels was significantly greater than that of CD4^- or TCRγδ IEL. It was demonstrated in situ for the first time that IEL adhered selectively to the villus microvessels of the small intestine partly via β₇ and MAdCAM-1.