Production and Evaluation of Antibodies for the Radioimmunoassay of Gastrin

In order to produce antibodies for use in radioimmunochemical determination of gastrin in serum, 41 guinea pigs and 72 rabbits were immunized; 15 different immunization schemes were employed; 23 animals (1 guinea-pig and 22 rabbits) produced detectable antibodies to gastrin. The antisera could bind 50% of 3 fmol (˜ 7 pg) 125I-gastrin in dilutions varying from 1:125 to 1:128,000. The binding energy expressed by the average association constant, K0, ranged from the order of 107l/mol to 1012l/mol. Only three antisera had antibodies with sufficient binding energy for radioimmunochemical determination of low physiologic concentrations of serum-gastrin (K0≥1011l/mol). One of these antisera reacted with cholecystokinin to an extent that made it unsuited for gastrin determinations in biologic fluids. The remaining two antisera were both in respect to dilution, binding energy, and specificity well suited to radioimmunoanalysis of gastrin in serum. On the basis of binding studies it appeared that 11 of the 23 gastrin antibodies were relatively homogeneous: the index of heterogeneity in these antibodies was ≥ 0.95. The high degree of homogeneity may be utilized in that straight-lined Scatchard plots may be used instead of standard curves. Otherwise the homogeneity is of no significance for the radioimmunoassay.