Peripheral lymph node-specific and Peyer's patch-specific homing receptors are differentially regulated following lymphocyte activation.

The MEL-14 receptor (MEL-14 R) expressed by murine lymphocytes represents the peripheral lymph node-specific homing receptor, and is essential for murine lymphocytes to specifically adhere to high endothelial venules (HEV) of the peripheral lymph nodes and to ultimately migrate in vivo into the parenchyma of this lymphoid organ. A Peyer's patch-specific homing receptor, termed LPAM, is now appreciated to mediate murine lymphocyte adhesion to Peyer's patch HEV. We previously demonstrated that the cell surface density of the MEL-14 R was markedly reduced following PMA-induced protein kinase C activation of lymphocytes. In the present study, we investigated the phenotypic and functional expression of LPAM by murine lymphocytes exposed to PMA. The results show that the surface expression of LPAM on activated lymphocytes remains constant under conditions where MEL-14 R is downregulated significantly. Additionally, the surface expression of LPAM is not influenced by calcium ionophore, either alone or in combination with PMA, whereas the PMA-induced loss of MEL-14 R is synergized by calcium ionophore. Therefore, LPAM and MEL-14 R expression are differentially regulated by activated murine lymphocytes. LPAM expressed by TK1 (Peyer's patch HEV-binding murine lymphoma) and MEL-14 R expressed by 38C13 (peripheral lymph node HEV-binding murine lymphoma) were found to be regulated by the consequences of PMA activation in a pattern similar to that of normal lymphocytes. Furthermore, we provide evidence that MEL-14 R internalization is not involved in the loss of the receptor expressed by activated lymphocytes.(ABSTRACT TRUNCATED AT 250 WORDS)