Characterization of a feline homologue of the βE integrin subunit (CD103) reveals high specificity for intra-epithelial lymphocytes

The characteristics of a feline homologue of the αE integrin (CD103), defined by two murine monoclonal antibodies, Fe7.1B8 (IgG1) and Fe7.2D8 (IgG1), are described. These antibodies recognized 75% of intra-epithelial (range 59-88%) and 40% of lamina proprial (range 28-46%) T cells of the intestinal mucosal tissue of the small intestine in contrast with approximately 2% of peripheral blood lymphocytes. Both antibodies immunoprecipitated a 180 kDa protein from biotinylated feline intra-epithelial mucosal leukocytes consistent with the αE integrin subunit in conjunction with a 120 kDa protein consistent with the β7 subunit. The nucleotide sequence of feline αE integrin, generated from molecular cloning of the feline αE encoding cDNA, is also reported. This feline molecule shares 72% sequence homology with human and 69% homology with murine and rat counterparts. Homology includes the presence of an X (extra) domain, that appears unique to αE molecules as described for human, rat and mouse, as well as areas of homology common to other α integrins. Of note is a typical I (inserted) domain, the presence of seven repeat regions, and highly conserved sequences in the cytoplasmic tail. Transfection studies demonstrated that both antibodies recognized an extracellular component which encompassed the X and I domains of the cloned αE integrin subunit. These studies demonstrate that the pattern of tissue distribution, biochemical characteristics, and cDNA sequence of the feline αE integrin subunit are largely similar to that described for other species.