Quantitative IgE- and IgG-subclass responses during and after long-term ragweed immunotherapy

We studied the quantitative responses of short ragweed (RW)-pollen-specific serum antibodies in 22 patients with RW immunotherapy (IT) and in a different set of 31 patients, 16 of whom stopped RW IT after more than 5 years of treatment. Serum was assayed before and after season, 1 year before and 1 and 2 years after starting IT, and 1 year and 2 years after stopping IT. RW pan-IgG, RW IgG1, and RW IgG4 were measured by ELISA, and RW IgE by RAST. Absolute quantities of RW IgG1 and RW IgG4 in reference sera were estimated by least-squares multiple regression analysis of 223 sera with the equation RW pan-IgG = RW IgG1 + RW IgG4. IgG1 is dominant in the early immune response of IT and disappears relatively slowly when IT is stopped. In contrast, IgG4 appears in significant quantities only after prolonged IT and disappears rapidly when IT is stopped. The apparent average half-life of RW IgG4 (9 months) was significantly shorter than that of RW IgG1 (29 months) (p less than 0.001). Before IT, mean RW IgE rose 180% (p less than 0.01) during the RW pollination season (August to November). This seasonal rise in RW IgE was ablated after IT from 1 year up to 8 years, but returned the year after IT was stopped. After 2 years of IT, the RW IgG1 and IgG4 levels were significantly correlated with RW IgE (r = 0.94 and 0.81; p = 0.0001 and 0.005).