Cross allergenicity among grasses determined by tissue threshold changes.
Twenty-seven volunteers with grass-pollen allergy who had not received prior immunotherapy had titrated prick tests with fivefold dilutions of 10 grasses (timothy, Bermuda, smooth brome, grama, salt, quack, western wheat, Johnson, June, and Bahia) to a final dilution of 1:3,906,250 w/v. Ten subjects served as untreated control subjects. Seventeen subjects received immunotherapy with an extract containing equal parts of timothy and Bermuda. Twelve months later subjects had repeat titrated skin testing with reconstituted aliquots of the same lyophilized extract, at the same time of day, and at the same location on the back as in the initial testing period. Nine treated subjects and eight control subjects completed the study protocol. The skin test areas with all 10 grass extracts were significantly decreased in the treated group compared to the control group (p less than 0.01), and there was no difference in the extent of the reduction among the 10 grasses by analysis of variance. We conclude that immunotherapy to timothy and Bermuda alone is capable of reducing to a similar degree the clinical sensitivity to all 10 grasses studied. The results of this study suggest that treatment with timothy and Bermuda alone may be sufficient in most grass-sensitive individuals.