CD44 is not directly involved in the binding of lymphocytes to cultured high endothelial cells from peripheral lymph nodes.

The Ager assay was adapted to a porcine lymphocyte-rat high endothelial cell (HEC) system. Using this in vitro assay, the role of porcine CD44 in lymphocyte binding to HEC was examined. The results show that the presence of soluble CD44 molecules did not inhibit the binding of porcine lymphocytes to the cultured rat HEC. Treatment of lymphocytes with anti-CD44 monoclonal antibodies (mAb), or with papain, which removes a 45,000 MW peptide from the intact CD44 molecule, did not inhibit the binding. Binding to the rat HEC did not induce modulation of CD44 molecules on the cell surface. Furthermore, modulation of the CD44 molecule by biotinylated anti-CD44 antibody followed by streptavidin-phycoerythrin, which had caused the molecule to cap on the cell surface, did not prevent the cells binding to the HEC. Similarly, cells denuded of CD44 by anti-CD44 antibody retained the capacity to bind to HEC. Moreover, the binding cells were mainly those which had been stripped of CD44 by the antigenic modulation. It is concluded that CD44 is not directly involved in the binding of lymphocytes to the cultured HEC from peripheral lymph nodes (PLN).