HISTAMINE HYPERSENSITIVITY INDUCED BY PASSIVE SENSITIZATION OF HUMAN BRONCHUS - EFFECT OF SERUM IGE DEPLETION

Background Sensitivity to specific allergens and increased sensitivity to common spasmogens an characteristic features of allergic asthma an d are: also features demonstrated by tissues passively sensitized with serum from atopic donors, displaying high levels of IgE. It is eviden t that the specific response to allergen is related tc, circulating le vels of allergen-specific IgE, but it is unclear whether the histamine hypersensitivity is also related to this immunoglobulin. Objective Th e objective was to deplete IgE in the serum of a donor with high level s of total and allergen-specific IgE and compare specific-allergen sen sitivity and sensitivity to histamine in tissues passively sensitized with either the whole serum or the IgE-depleted serum. Methods Serum f rom a Dermatophagoides farinae-sensitive asthmatic (total IgE = 1047 U /mL, D, farinae-specific IgE > 17.5 U/mL) was subjected to an immunoma gnetic separation technique to reduce the levels of IgE (total and spe cific) to below 10 U/mL. Bronchial tissue from six non-atopic donors w as then passively sensitized overnight with either the whole serum or IgE-depleted serum and D. farinae and histamine sensitivity were evalu ated the next day using standard organ bath techniques. Results Passiv e sensitization with the whole serum resulted in the development of se nsitivity to D, farinae and increased sensitivity to histamine (750 +/ - 169 mg contraction to 10 U/mL D. farinae, histamine pEC(50) 5.64 +/- 0.16 and Ii-ax, 813 +/- 109 mg in sensitized vs 37 +/- 34 mg contract ion to 10 U/mL D. farinae histamine pEC(50) 5.05 +/- 0.23 and max. 490 +/- 84 in non-sensitized tissues, P>0.05). Incubation with IgE-deplet ed serum still produced histamine hypersensitivity (histamine pEC(50) 5.57 +/- 0.16 and max. 737 +/- 70 mg P > 0.05), but no significant res ponse to allergen was detected (20 +/- 13 mg contraction to 10 U/mL D. farinae). Conclusion These results demonstrate, that increased reacti vity to histamine and airway contraction to allergen induced by passiv e sensitization, occur through independent mechanisms and that, unlike allergen-sensitivity, histamine hypersensitivity is caused by a serum factor other than IgE.