The potency and antigen E content of commercially prepared ragweed extracts

This study compares several methods for their ability to evaluate the potency of commercial extracts of ragweed pollen extract. Samples of short ragweed pollen allergenic extracts were purchased from six commercial manufacturers and were assayed for antigen E and PNU content, as well as for reactivity in ragweed-sensitive human beings by direct skin test and by in vitro histamine release. Human reactivity correlated extremely well with the antigen E content of the extracts despite great variations in the amounts of antigen E present. The PNU content as labeled or as assayed in our laboratory showed no correlation with either antigen E content or degree of reactivity. There was a hundredfold or greater difference between the antigen E content and corresponding biologic activity of extracts labeled to have the same PNU content. Results indicate that double diffusion determinations of antigen E content would be a satisfactory method for the standardization of the potency of ragweed pollen allergenic extracts.