Do mucosal mast cells contribute to the immediate asthma response?

In rat trachea, two types of mast cells have been identified, connective ti ssue mast cells (CTMCs) and mucosal mast cells (MMCs). We previously report ed that CTMCs play an important role in tracheal contraction in vitro via 5 -hydroxytryptamine (5-HT) release in a rat model. In this study, we investi gated whether MMCs also play a role in tracheal contraction by employing ma st cell-deficient (Ws/Ws) rats and their congenic (+/+) rats. Rats were act ively sensitized with ovalbumin and challenged with it 2 weeks later. To ex clude the influence of CTMCs, rats were pretreated for 7 days with compound 48/80 injected i.p. in increasing doses. Histological study confirmed that degranulation occurred in CTMCs, but MMCs still remained. Histamine levels in trachea decreased to 9.31% of control levels. Ovalbumin-specific IgE pr oduction showed a time-dependent increase in both Ws/Ws and +/+ rats after sensitization with no significantly different values between the two groups . Ovalbumin challenge caused contraction of the trachea in sensitized contr ol (+/+) rats, but not in sensitized Ws/Ws and compound 48/80-pretreated +/ + rats. Ketanserin inhibited the contraction, but leukotriene antagonist ON O-1078 did not, indicating that the contraction was due to 5-HT, whereas le ukotriene, a mediator specific derived from MMCs, has no significant effect . The results suggest that MMCs has minimal, if any, contribution to trache al contraction and might have another function. Furthermore, Ws/Ws and the congenic rats provide a good model for studying the role of mast cells in t he immunologic response in airways.