Abstract
The specific binding of vasoactive intestinal peptide (VIP) to murine lymphocytes was investigated. CD4 T cells from mesenteric lymph nodes (MLN) bound more 125I-VIP than did unseparated MLN lymphocytes at 37°C, but not at 4°C. The differences between the amount of 125I-VIP bound by the CD4 T cells and unseparated MLN lymphocytes at 37°C depended upon a difference in the amount of the ligand that was internalized by the cells. The rate of insertion of unoccupied VIP receptors from the cytoplasm into the cell membrane (370 receptors/cell/min), the rate constants for internalization of ligand occupied VIP receptors (0.55 min −1) and unoccupied VIP receptors (0.11 min −1), and the rate constant for the elimination of internalized VIP (0.07 min −1) by CD4 T cells were evaluated. These results provide new understanding of the behaviour of VIP receptors on lymphocytes and indicate a mechanism by which CD4 T lymphocytes can homologously regulate their surface expression of VIP receptors in the presence of ambient VIP.
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