Toward the development of a standard reference cholera antitoxin

The need for a reference cholera antitoxin to serve as a standard for the calibration of cholera enterotoxin and toxoid as well as for measurement of the antitoxin response in animals and patients was recognized by the NIH Cholera Advisory Committee, NIAID, DHEW, USA. Two cholera antitoxins have been used for several years as provisional references, but neither was considered to embody all of the properties of an ideal standard. Accordingly, a lot of cholera antitoxin was prepared by immunization of goats with a formalinized, highly purified cholera toxin adsorbed on aluminum phosphate adjuvant. Booster injections were given at 8, 16 and 24 weeks. Plasma samples obtained from the 25 to 27 week bleedings were converted to serum, pooled, and freeze-dried. This serum possessed both high and constant toxin neutralizing activity in rabbit skin, rabbit ileal segment, mice, Y-1 adrenal cells and Chinese hamster ovary cells, and had high avidity by the rabbit skin assay. Hemagglutination tests gave identical values. It was shown to be highly specific by gel diffusion, but flocculation was relatively poor. On the basis of specificity, high avidity and toxin-neutralizing capacity this goat antitoxin (NIH Lot 1) was considered superior to previous provisional standards and is proposed as a satisfactory standard reference reagent.