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Summary The fractions obtained from purified rabbit antihapten antibody by papain digestion, which contain the antibody combining site (ADDS or ADS-I), were unable to sensitize the skin of the guinea pig for PCA or RPCA reactions. These fractions, however, when mixed with the intact antibody specifically inhibited the latter from producing PCA reactions showing that they can combine in vivo with the antigen. From a kinetic study it was concluded that these fractions diffuse away faster from the injection site than does the intact antibody. These fractions showed a precipitation line in agar double diffusion with horse-anti-rabbit γ-globulin. The fraction without antibody combining site (ADDP) can produce good RPCA reactions. It was concluded that the failure of ADDS and ADS-I to produce PCA or RPCA reactions is due to their inability to be “fixed” to the guinea pig tissues and that this “fixation” site is present on ADDP.
Óváry et al. (Wed,) studied this question.