Immunogenicity of cholecystokinin octapeptide-conjugated antigens in pigs

An improved antigen is required to raise antiserum titers against cholecystokinin higher than those observed in previous studies to demonstrate the effect of immunoneutralization of cholecystokinin on feed intake in swine. Four immunogenic carrier proteins were compared. Unsulfated cholecystokinin octapeptide (CCK8ns) was conjugated to each of human serum globulin (HSG), BSA, Keyhole limpet hemocyanin (KLH), and Tuberculin purified protein derivative (PPD). Forty crossbred swine (four from each of 10 litters, 78 d of age, 22 kg BW) were randomly assigned to the four conjugated antigens by litter. The primary and three booster doses of antigen were injected at 14-d intervals. A blood sample was drawn before the primary dose on d 1 to assess basal nonspecific binding of antigen. Additional blood samples were drawn on d 22, 29, 36, 43, 50, 57, 71, and 92 to follow the time course of antiserum titer expression (d 1 = day of primary dose). Titer is the serum dilution that binds 50% of 1 fmol of radiolabeled antigen. Titers, compared by ANOVA of log titer values, were different between antigens (P < .01) and between litters (P < .01). Mean titer (n = 40; 10 pigs, four samples/pig) during the period after the immune response (d 50, 57, 71, and 92) was 55, 115, 176, and 535 for BSA, HSG, KLH, and PPD, respectively. It is concluded that the carrier protein component has an important effect on immunogenicity of conjugated CCK antigens in pigs; BSA was inferior and KLH and PPD were superior to HSG.