Regulation of histamine receptor concentration on human PBMC by homologous hormone

Human peripheral blood mononuclear cells (PBMC) preincubated with 10(-3)M histamine at 37 degrees C, washed and incubated with 3H-histamine showed a reduction in the binding of the labelled hormone as compared to cells which had not been pretreated with histamine. Using competitive binding assays it was further shown that the number of specific binding sites for histamine was reduced by 46-62%. However, the affinity of receptors as indicated by Kd values remained unaltered. It would thus appear that elevated levels of histamine lead to down-regulation of histamine receptors on human PBMC with a quantitative reduction in the number of binding sites without an alteration in their affinity characteristics. In view of the fact that histamine receptors have been shown to be present on suppressor lymphocytes, the down-regulation of these receptor sites may have relevance in physiological and disease states where perturbations in the levels of histamine are observed.