Detection of a Tyrosine Phosphatase LAR on Intestinal Epithelial Cells and Intraepithelial Lymphocytes in the Human Duodenum

摘要

Studies of tyrosine phosphorylation in the human duodenum have indicated that proliferating cells in the middle portion of the duodenal crypt were devoid of this feature, suggesting that tyrosine kinase activation is not a dominant factor in crypt cell proliferation, and that consequently tyrosine phosphatase activity may be a more critical factor in crypt cell development. We investigated the expression of the leukocyte common antigen-related receptor (LAR) family of tyrosine phosphatases. A flow cytometry system was used to examine cells from the surface, mid-portion, and lower part of the crypt. Individual cell populations were immunostained with anti-LAR antibodies using phycoerythrin-conjugated anti-CD3 to discriminate between epithelial cells (CD3⁻) and intraepithelial lymphocytes (CD3⁺). Epithelial cells expressed LAR throughout the crypt. Expression of LAR was maximal in the mid-portion of the crypt with lower expression at the top of the villi. Intraepithelial lymphocytes expressed low levels of LAR atthe tips of the villi with stronger expression extending towardsthe base of the crypt. These findings were confirmed byimmunohistochemistry on paraffin-fixed sections. Of note,peripheral blood lymphocytes expressed less LAR than IEL. Theseobservations suggest the possibility that tyrosine phosphataseLAR may be of importance in the regulation of crypt cellproliferation. Moreover, as the extracellular domain of LAR hashomology with adhesion molecules, the finding of this molecule onIEL could suggest a possible functional role in homing of thisunique lymphocyte.