Studies with marked antisera. Quantitative studies with antisera marked with iodine 131isotope and their corresponding red-cell antigens

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Abstract
Antisera marked with I131 were used in an attempt to study quantitatively the interaction of serum antibodies and red cell antigens. Studies were made on in-agglutinable systems. These were "inagglutinable" bovine cells with Il31-marked rabbit anti-bovine red cell and Il31-marked human infectious mononucleosis sera, and also human cells with I131I-marked human Rh incomplete anti-D sera. Non-specific adsorption which interfered with quantitative detns. was avoided by pretreatment of the cells with unmarked serologically compatible sreum. The ratio of I uptake by the gamma-globulin fraction of serum to that of whole serum passed through a max. (0.92) with an I content of about one atom per protein molecule (assumed avg. mol. wt. of 105). The amt. of Paul-Bunnell antibody (in terms of ll31-marked serum protein) in an infectious mononucleosis serum was found to be about 40[mu]g./ml. serum (7% protein). In the same terms, the amt. of D-antibody in an incomplete Rh antiserum was estimated at 54[mu]g. The number of Paul-Bunnell sites on a single bovine red cell was found to be considerably greater than the number of D sites on a human Rh-positive cell (CDe/CDe). The implication of these results is discussed in the light of observed serological phenomena.