PRODUCTION OF ANTIIDIOTYPIC ANTIBODIES RESEMBLING BOVINE SOMATOTROPINBY ACTIVE IMMUNIZATION OF LACTATING COWS

Anti-idiotypic antibodies produced in lactating cows by immunization w ith rabbit antibodies raised against bovine somatotrophin (bST) were e valuated for bST-like immunoactive and biological activities. Twenty N ew Zealand White rabbits were immunized against bST. Serum was purifie d using protein A-Sepharose CL-4B and bST-Sepharose 4B affinity chroma tography to yield specific anti-bST immunoglobulin G (IgG). Twenty-fou r lactating cows were allocated to a randomized complete block design and were immunized with either: (1) rabbit anti-bST (n=12) or (2) non- specific rabbit IgG (n=12, control). Cows were immunized starting at d ay 68 of lactation with 800 mu g antigen emulsified with Freund's comp lete adjuvant and 1 mg Quil A administered by i.m. injections. Repeate d immunizations of 800 mu g antigen in Freund's incomplete adjuvant an d 1 mg Quil A followed after 3 weeks and then every 5 weeks throughout lactation. Serum samples were collected twice weekly and were analyse d for anti-rabbit IgG titre and immunoactive bST concentration by radi oimmunoassay. All cows developed antibodies against rabbit IgG by the second and third immunizations. With rising titres, immunoactive bST c oncentrations increased in cows treated with anti-bST following each o f the six repeated immunizations to 4.7+/-3.3, 10.0+/-4.2, 12.0+/-4.8, 17.3+/-6.7, 24.0+/-10.0 and 36.3+/-20. 4 ng/ml (mean+/-S.E.M.) compar ed with controls (0.81+/-0.09 ng/ml, overall mean+/-S.E.M.). To assess the biological activity of these bST anti-idiotypic antibodies, milk yield and serum insulin-like growth factor-I (IGF-I) concentrations we re analysed in all cows and a subset of six cows per treatment respect ively. Milk production and IGF-I concentrations were unaffected by ant i-bST immunization.