Suppression of late-phase skin reactions by immunotherapy with ragweed extract.

The cutaneous late-phase reaction (LPR) to ragweed was studied in untreated ragweed-allergic individuals and patients receiving 3 to 5 years of immunotherapy demonstrating clinical improvement. The magnitude of immediate skin reactions and the initial levels of the specific IgE and IgG antiragweed antibodies were similar in both groups. The LPR was elicited by administering a skin test with ragweed extract at 10 times the concentration required to elicit a 4 + immediate reaction and appeared as an erythematous-edematous lesion associated with pruritus. In the untreated group 94% developed an LPR (59 +/- 32 mm at 4 hours and 67 +/- 30 mm at 8 hours) at this dose. In the treated group only one third developed an LPR, one third had partial response measurable at one of these two times, and one third failed to develop any LPR (21 +/- 20 mm at 4 hours, p less than 0.002, and 20 +/- 22 mm at 8 hours, p less than 0.001). Therapy resulted in a twentyfold increase of IgG antiragweed level and in a decline of IgE antiragweed. The size of the LPR correlated inversely with the level of IgG antiragweed (p less than 0.01; r = -0.52) but not with IgE antibody. Thus, in a retrospective analysis immunotherapy was associated with the suppression of the skin LPR, and the magnitude of the LPR was correlated with the level of IgG antiragweed. We suggest that the clinical efficacy of immunotherapy is related in part to effects on the LPR.