In vitro lymphocyte stimulation by concanavalin A and with histamine as a co-mitogen in dogs with atopic dermatitis

Cell-mediated immune function was assessed in a group of dogs with atopic dermatitis by measuring the responses of peripheral-blood lymphocytes (PBL) to various concentrations of Concanavalin A (Con A) and comparing them to those of normal dogs. No difference from normal was found in any of the stimulation indices neither was spontaneous tritium uptake of unstimulated cells different between the groups. We also measured the response to Con A stimulation in vitro of PBL preincubated for 24 h, either in cell-culture medium at 37 degrees C, or in whole blood containing EDTA at room temperature, as an indirect measure of function of a subgroup of suppressor cells. Preincubation caused enhancement of mitogenesis for normal dog lymphocytes but not for the atopic dog cells, particularly for suboptimal concentrations of Con A. No differences were found in the responsiveness following incubation in cell-culture medium between normal and atopic dog cells but for both groups the cells preincubated in whole blood were generally more responsive. Histamine, which is one of the mediators of type 1 hypersensitivities such as atopy, can modulate lymphocyte function. At 10(-4) and 10(-8) M histamine, when added simultaneously with Con A, enhanced mitogenesis of normal dog PBL but suppressed mitogenesis of atopic dog PBL. By using histamine H1 and H2 antagonists, we concluded that histamine enhanced mitogenesis via H1, receptors and suppressed it via H2 receptors. Our results suggest that there are abnormalities in lymphocyte function in dogs with atopic dermatitis which may be important in the pathogenesis of the disease.