Irradiation of antibody causes marked changes in the precipitin curve, at first causing a progressive increase in the antibody/antigen ratio of the specific precipitates and later rendering the antibody non-precipitable though it remains co-precipitable with unirradiated antibody. During these changes there is no decrease in the amount of antibody recoverable from irradiated solution. The sensitivity of irradiated antibody to antigen excess is greater than that of normal antibody, so much so that there may be less precipitate from a mixture of normal antibody, irradiated antibody and excess antigen, than from the same amount of normal antibody and antigen alone.Irradiation of antigen affects the precipitin curve in a manner opposite in most respects to that occurring when antibody is irradiated.It is shown that the ability of the irradiated antibody to produce passive anaphylaxis is considerably reduced while the precipitin reaction is as yet relatively little affected.Changes in the ultraviolet absorption spectra of irradiated globulin solutions and the immune precipitates thereform have been observed and are discussed in relation to the changes in antibody and antigen reactivity.The meaning of these findings in relation to the mechanism of the precipitin reaction is discussed.
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