Identification and characterization of [125I]arginine vasopressin binding sites on human peripheral blood mononuclear cells.

Arginine vasopressin (AVP) is a nonapeptide that has been shown to be released from the posterior pituitary during stress. Although noted primarily for its hemodynamic and homeostatic properties, AVP also appears to have an effect on the immune system. It may modulate cellular immunity via its enhancement of the autologous mixed lymphocyte response (AMLR), an effect which we have demonstrated to occur over a wide dose range with a maximum at 10(-7) M. In this study, we examined the binding of [125I]AVP, and AVP analogues to human peripheral blood mononuclear cells (PBMC). AVP inhibited [125I]AVP (0.2 nM) binding on PBMC in a dose-dependent manner with maximal inhibition being reached at 10(-8) M. Specific [125I]AVP binding, as defined as that which could be displaced by 1 x 10(-6) M AVP, was saturable, time-dependent, and linear to cell concentration. Specific binding reached saturation at approximately 1000 pM in 45 minutes. From Scatchard analysis of saturation experiments it appeared to be a homogeneous population of binding sites with KD of approximately 0.5 nM and Bmax of approximately 7.6 fmole/8 x 10(6) cells, corresponding to approximately 527 binding sites/cell. There was a good correlation between AVP binding and cell number. AVP failed to dissociate completely from its binding sites in 60 minutes, perhaps because of the formation of a high-affinity ligand-binding site complex. From competitive binding studies with various AVP antagonists and analogues, it was found that the AVP binding site appeared to be V1-like. AVP binding occurred predominantly on B-cells and macrophages. Having provided evidence for the existence of specific, high affinity, and saturable V1-like AVP binding sites, we suggest a potential modulatory role for AVP in the communication between the neuroendocrine and immune systems.