A unique high-titer antiserum to gastrin

Among twenty rabbits immunized with hexadecapeptide gastrin coupled to bovine serum albumin, one (No. 4562) produced, after four immunizations, antisera with a titer of 10⁸. The titer remained above 10⁷ for 8 months without boosting. Upon storage the titer declined to 4 ± 10⁶ after a year irrespective of storage conditions. The titer has remained stable at this level for 5 years, After the third immunization the avidity has remained high, K^o _eff. varying from 9 to 5 ± 10¹² l/mol. The antiserum binds the bioactive C-terminus of gastrin. Using tyr-12 monoiodinated gastrin as tracer, ID₅₀ gastrin-17 (ns); ID₅₀ cholecysto-kinin-33 is 0.026. Sulphated gastrins are bound less well than non-sulphated forms, ID₅₀ gastrin-17 (ns) ID₅₀ gastrin-17 (s) being 0.08. For gastrin component I and gastrin-34 ID₅₀ gastrin-17 (ns): ID₅₀ gastrin-34 (ns) or component I is 0.7. The binding homology of the antiserum is high, α (the heterogeneity index) varying between 0.68 and 0.85. Samples of the antiserum have now been distributed to more than 200 laboratories for radioimmunoassay, immunosorption and immunocytochemistry.