The lack of effect of histamine--protein conjugates on human lymphocyte responses to concanavalin A and histamine.

We have studied the effect of depleting human peripheral blood lymphocytes (PBL) on plates coated with histamine-rabbit serum albumin (H-RSA) or control (E-RSA) conjugates, on the concanavalin A (Con A) response and the histamine suppression of Con A responses. Low H10-RSA-substituted conjugate depletion had little effect on [3H]-thymidine incorporation of Con A-stimulated cells compared to control (E10-RSA) conjugates and unseparated cells, but significantly increased unstimulated cell counts, therefore reducing stimulation index (SI). Highly histamine-substituted (H30-RSA) and control (E30-RSA) conjugates decreased SI in a similar way, but also decreased the [3H]-thymidine incorporation of Con A-stimulated cells. Histamine suppression of Con A responses was reduced by both E10- and H10-RSA-coated plates at suboptimal but not optimal mitogen concentrations. The induction of Con A-induced suppressor cells was unaffected by prior depletion of cells on H10- or E10-RSA conjugate-coated plates. Addition of H10- and E10-RSA to Con A cultures had a slight enhancing effect on transformation, but no effect on histamine suppression of the Con A response. Thus, whilst it is clear from other studies in vitro that functional histamine receptors are present on suppressor T cells, the results presented here show that histamine-protein conjugates do not specifically bind to histamine receptor-bearing human peripheral blood suppressor T lymphocytes.