Given an abstract, generate a keyword (a noun phrase) that best describes the focus or contribution of the paper. Such keywords can be directly from the given abstract or outside it.
Q: Abstract: Fifty ragweed-sensitive subjects were each administered a course of 12 injections of polyethylene glycol-modified ragweed extract. To investigate the effect of two treatment regimens, subjects were paired according to their skin sensitivity to ragweed extract and the severity of their rhinoconjunctivitis the previous year. One of each pair was randomly allocated to receive injections at weekly intervals, and the other subject was to receive injections daily until a local or systemic adverse reaction occurred and then to switch to a weekly schedule for the rest of the course. Blood was obtained immediately before each injection and at the end of the study to examine the rates of change of ragweed-specific IgE and IgG antibody levels and to evaluate whether these or other variables could be used to predict the occurrence of adverse reactions. Immediate reactions were minimal in both groups, but more late reactions occurred in subjects receiving the modified rush regimen; therefore, although the total number of injections received by the two groups was similar, the total dose of protein injected in the rush group was only half that achieved in the weekly group. Treatment induced increases in ragweed-specific IgE and IgG antibodies in both groups; the increase in IgE was similar in the two groups, but the increase in IgG was higher in the weekly group. There was a marked decrease in skin sensitivity to ragweed extract after treatment that was directly related to the IgG antibody response, and therefore, these changes were greater in the weekly group.(ABSTRACT TRUNCATED AT 250 WORDS)
A: 
Allergens