Production and Characterization of Therapeutic Anti-idiotypic Antibodies for Control of Diarrhea Caused by Escherichia coli K88

Polyclonal anti-idiotypic antibodies (pAb2) were produced in laying hens against monoclonal (mAb) and polyclonal (pAb) antibodies that recognized Escherichia coli K88 fimbrial antigen. pAb2 against anti-K88 pAb inhibited binding of K88 fimbriae to Ab1 by 30-35 % while pAb2 against anti-K88 mAb inhibited the binding by 6-15 % when tested by competitive ELISA. Pure pAb2 were injected into mice to produce Ab3. Ab3 was able to recognize K88 fimbriae with the reaction being stronger for Ab2 derived from anti-K88 rabbit Ab1 than that of Ab2 derived from the corresponding monoclonal antibodies (mAb1). The immunized mice were challenged with an IP injection of 5X108 CFU of E. coli K88. The serum pAb3 provided complete protection against death (100% survival) in two experiments. In contrast, the survival rate in the non-immunized mice in the two experiments were 25 and 18%. A second study was undertaken to evaluate the passive efficacy of two pAb2 preparations (pAb2 produced against rabbit anti-K88 IgG2a and its Fab) when administered orally to neonatal piglets challenged with E. coli K88. Partial protection (50 % survival rate) was observed in the pAb2 treated piglets, while only 13.5 % of control piglets (no-pAb2) survived. Our results indicates that pAb2 not only are excellent surrogate antigens for immunization, but can also provide considerable protection when used for passive immunization.