Passive sensitization of human airways induces mast cell degranulation and release of tryptase

Background: This study was designed to examine the effect of passive sensitization (PS) on human bronchial mast cells. PS with asthmatic serum induces a hyper-responsiveness to nonspecific agonists, and immunoglobulin (Ig) E binding mainly on mast cells. Methods: Bronchi dissected out from 19 lung specimens were incubated in normal or asthmatic serum. Immunohistochemistry was performed using monoclonal antibodies (MoAbs) directed against tryptase, chymase, or c-kit. Mast cells were classified as fully granulated (type I), partly (type II) or largely degranulated (type III). Tryptase was measured in supernatant using ELISA. Contractile response was recorded in a separated set of experiments using an organ bath system. Results: PS decreased both tryptase positive cells (47.9+/-10.0 vs. 26.7+/-4.8 cell/mm(2), P = 0.003) and chymase positive cells (26.1+/-3.3 vs. 14.9+/-1.8 cell/mm(2), P = 0.01), but did not alter the number of c-kit positive cells. PS decreased the proportion of type I (55.4 vs. 28.9%, P < 0.0001) and, concomitantly increased that of types II (23.2 vs. 41.0%, P < 0.0001) and III (21.4 vs. 30.1%, P = 0.04). Following PS, tryptase concentration significantly increased and the magnitude of histamine response, was correlated with the amount of type II mast cells. Conclusion: PS of human isolated bronchi induces a mast cell degranulation related to in vitro hyper-responsiveness, along with a tryptase release.