The role of ragweed pollen in autumnal asthma

Thirty-nine ragweed-allergic seasonal asthmatics were studied from 1972 to 1974. After quantitative skin tests, antigen E-induced leukocyte histamine release, quantitative inhalation bronchial challenge with ragweed extract to determine PD35 (provocation dose of allergen causing 35% decrease in specific airways conductance), and radioallergosorbent test (RAST) determinations were done, patients were paired based on PD35 values and randomly assigned to treatment or placebo groups, receiving either aqueous ragweed extract or placebo prior to the 1973 ragweed season. Treated patients received a mean cumulative dose of extract equivalent to 11.7 microng antigen E (4,180 protein nitrogen units PNU]). Twenty-nine patients were followed through the ragweed season with daily symptom diaries and biweekly physician examinations. Severity of disease was not predictable by PD35 data, skin tests, leukocyte histamine release, or radioallergosorbent test (RAST) values. Although all patients were ragweed-allergic by objective tests, only 13/29 had asthma symptoms correlating with ragweed counts. Mold spore counts were related significantly to symptoms in some patients. Asthma and hay fever symptoms correlated significantly in 24/29 patients. This dose of immunotherapy caused no significant difference to be found in asthma or hay fever symptoms in treated versus placebo patients for the 1973 reporting period as determined by physician evaluations or daily symptom diaries. No patients showed significant improvement in PD35 values after treatment in 1973. Similar findings were obtained for a smaller group of patients followed through the 1974 ragweed season who received a mean dose of 31.2 microng antigen E (11,140 PNU). The failure of these patients to show a response to immunotherapy could be due to a combination of the relatively low dose of ragweed extract and their sensitivity to other allergens.