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Background Effects of mast cell-released histamine on smooth muscle and endothelial cells are considered as responsible of immediate symptoms of anaphylaxis. However, little is known about histamine effects on Th2 lymphocytes, which orchestrate the allergic reaction upstream of mast cells. Objective We addressed this question in house dust mite (HDM) allergics, according to the presence of rhinitis or asthma and allergen stimulation. Methods Peripheral blood mononuclear cell from 15 rhinitic and 14 asthmatic HDM-allergic subjects and 16 controls were cultured with Der p 1 or histamine. The effect of Der p 1 on histamine receptor (H1R and H2R) expression was studied. T-cell cytokine production was studied upon Der p 1 or histamine stimulation. The role of H1R in histamine effects was assessed with levocetirizine. Results H1R and H2R are overexpressed on T cells from asthmatic but not from rhinitic subjects. Der p 1 increases H1R expression on CD4+ cells from both allergic groups, and decreases it in controls, on CD4+ and CD8+ subsets. Der p 1 decreases T-cell H2R expression in asthmatics. Allergen increases IL-4 and IL-13 in both allergic groups. Histamine increases Th2 cytokines in rhinitics only, and levocetirizine abolishes this effect. In asthmatics and controls, histamine decreases T-cell cytokines through a non-H1R dependent pathway. Conclusion In rhinitis but not in asthma, histamine is able to increase allergic inflammation by increasing Th2 cytokine production in a positive feedback dependent on H1R. This result could explain in part why H1R antagonists, are very efficient in rhinitis, but not in asthma. Cite this as: K. Botturi, Y. Lacoeuille, D. Vervloet and A. Magnan, Clinical & Experimental Allergy, 2010 (40) 755–762. [ABSTRACT FROM AUTHOR]

The article examines the relationship between T cells and allergens. According to the author, T cell activation in allergy is not as clear as it was initially presumed. The author states that there is a global predisposition to allergy in atopic subjects attributed to deficient Treg cell machinery which allows the Th2 cell activation to occur in response to all antigens.