Atopic asthma is dominant in elderly onset asthmatics: possibility for an alteration of mast cell function by aging through Fc receptor expression.

The morbidity and mortality of elderly onset asthma have recently been on the increase. To evaluate the allergic status of the elderly onset asthmatics, we performed skin tests for allergens and estimated serum total IgE levels of the patients. The proportion of the skin-test-positive patients among the elderly onset asthmatics was significantly larger than that in the younger onset group, whereas no significant difference was observed in the frequency of patients with serum total IgE levels higher than the normal range (287.2 IU/ml). On the other hand, in the experiments with aged mice, isolated peritoneal mast cells (PMC) showed a considerable decrease in the FcgammaRIIB/III expression and higher degranulation triggered by 2.4G2, as compared to the PMC derived from young mice. Since FcgammaRIIB has been shown to act as a negative regulator, we speculate that in the aged mice Fc receptor-mediated mast cell function may be upregulated by a release from the negative regulation as a result of decreased FcgammaRIIB expression. Our results obtained from a mouse model system may help to understand pathophysiological mechanisms underlying elderly onset asthma.