Injection of low-dose antigen attenuates the response to subsequent bronchoprovocative challenge.

Injection of low-dose antigen on a co-seasonal basis has been proposed as an alternative to conventional immunotherapy in allergic disorders. Few studies of efficacy have been attempted, and available data do not support the use of this technique. We evaluated the effect of low-dose antigen injection in 21 subjects with histories of asthma, after exposure to animal antigen. Each subject was injected with low-dose animal antigen, as determined by skin test end point titration, or with placebo. Twenty minutes after the injection, bronchoprovocative challenge was performed with the use of the same antigen. The provocative dose 20% (PD20), FEV1 after antigen injection, was 28.52 +/- 1.74, was compared to 6.50 +/- 1.15 after placebo injection (p less than 0.01). This experiment was repeated after pretreatment of patients with indomethacin. The protective effect of antigen injection was abolished. In a third experiment, the PD20, FEV1 for methacholine, was 10.74 breath units (BU) after antigen injection and 6.84 BU after placebo injection (PD less than 0.05). Low-dose antigen injection causes rapid reduction of bronchial sensitivity to inhaled antigen and methacholine. This effect is abolished by treatment with indomethacin.