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In view of the prevalence of D. pteronyssinus in this country and its high allergenic potency, it is considered that this mite is an important factor in allergic asthma. IntroductionThe importance of the house-dust mite as a cause of allergic disease has only recently been recognized (Voorhorst et al.,

It has been previously reported by Thueson and his co-workers [1] that lymphokine-containing supernatant of cultured human peripheral blood lymphocytes stimulated with Concanavalin-A (Con-A) is capable of releasing histamine from human basophils. Here we confirm such findings, show that such release is additive to that due to immunological stimuli (Anti-IgE and antigen) and describe its characteristics and effect in lung tissue. The lymphokine was found to induce a small histamine release from chopped or enzyme-dispersed human lung tissue. As was the case with basophils, the release from lung tissue by this factor, though small, was also found to be additive to that induced by anti-IgE when both agents were added simultaneously. Histamine release from leucocytes by neat supernatant ranged from 9 to 35% and up to 55% when concentrated four-fold. The release resembled that of IgE-mediated reactions in many respects including temperature and calcium dependence, time course and susceptibility to metabolic inhibitors - thus suggesting a non-cytotoxic mechanism. These results show that histamine release by this lymphokine(s) possesses most of the features of an active secretory process. They also suggest that the histamine-releasing factor (HRF) in lymphokine-containing supernatants might be involved in the modulation of type I allergy in humans, apart from its involvement in delayed-type hypersensitivity.