EVIDENCE FOR A STRUCTURAL DIFFERENCE IN THE CD7 POLYPEPTIDE ON HUMAN THYMOCYTES AND INTRAEPITHELIAL LYMPHOCYTES DEFINED BY A NEW MONOCLONAL-ANTIBODY, 3D9

Intestinal intraepithelial lymphocytes (IEL) represent a distinct subp opulation of lymphocytes located on or above the basement membrane and adjacent to the basolateral membrane of enterocytes. Thus IEL are str ategically positioned to mediate a response to the uptake of foreign a ntigens or to the alteration of enterocytes by injury or infection. Be cause of their unique location, we hypothesized that IEL might selecti vely express specialized cell surface proteins important in their site -specific localization or function. To identify such proteins, we immu nized mice with purified human IEL and identified one monoclonal antib ody, 3D9, which was found to react with a majority of IEL but with ver y few lamina propria lymphocytes (LPL) and weakly with most peripheral blood lymphocytes (PBL). Evaluation of this antibody with two-dimensi onal gels demonstrated that it reacts with CD7, previously known as an early thymocyte differentiation antigen. Interestingly, unlike all ot her anti-CD7 monoclonal antibodies, 3D9 identified only occasional thy mocytes by immunohistochemistry suggesting that CD7 is structurally di fferent on IEL and thymocytes. However, the CD7 polypeptide immunoprec ipitated from IEL and thymocytes appeared identical in SDS-PAGE mobili ty and in charge by two-dimensional gels, despite being recognized dif ferently by monoclonal antibodies. These studies emphasize the express ion of CD7 by IEL T cells and reveal the existence of an undefined str uctural difference between CD7 molecules on IEL compared to thymocytes . (C) 1994 Academic Press, Inc.