The clinical and immunologic specificity of immunotherapy

In order to study the specificity of immunotherapy for respiratory allergy, a group of patients sensitive to both ragweed and grass pollens were selected. From 87 volunteers with a history of both spring and fall hay fever, 42 patients with evidence of strong sensitivity by basophil histamine release to both ragweed pollen and mixed grass pollen extracts were selected for study. On the basis of the histamine release data, the patients were divided into two groups matched for sensitivity to both grass and ragweed pollens. In 1970, May and June symptom diaries showed the two groups to suffer quite similar severity of symptoms during the grass pollination season. One group of patients was started on a preseasonal course of immunotherapy with alum-precipitated aqueous extract of ragweed pollen while the other group received placebos containing histamine. By fall there had been a considerable rise in IgG-blocking antibodies to ragweed in the treated group. Symptom diaries in August and September showed that the treated group showed significantly less severe symptoms than the placebo group. Both groups received booster injections at 2-wk intervals from the fall of 1970 to the fall of 1971. Doses in the treated group were raised to attempt to administer the largest possible dose. Again there was no difference in the symptoms reported by the two groups during the grass pollination season, but an even greater difference emerged between the two groups during the ragweed season. The following year 1972 the same results were obtained. These data demonstrate that treatment with ragweed pollen extracts has little or no effect on grass pollen symptoms and confirm that immunotherapy is clinically as well as immunologically specific. Antibody responses to the second year of high-dosage booster injections was not greater than responses to a comparatively short preseasonal course given the first year.