RESUMEN
In the present experiments the efficacy of murine and bovine monoclonal antibodies for passive immunization in cattle was compared. The in vivo immunoneutralization of pregnant mare serum gonadotrophin (PMSG) by murine and bovine antibodies after repeated administration was chosen as a model for this study. Results indicate that repeated injections of murine monoclonal antibodies against PMSG (mMCA) alone did not, or only to a small extent, elicit an anti-mouse immune response. The simultaneous administration of mMCA and PMSG resulted in relatively high levels of anti-mouse antibodies after the second injection, leading to a decrease in neutralizing activity of mMCA. The results suggest that the neutralizing activity of mMCA is inhibited more by anti-idiotypic than by anti-isotypic antibodies against mMCA. In vivo, the bovine monoclonal antibody against PMSG (bMCA) only partially neutralizes PMSG. After repeated administration of bMCA, either alone or in combination with PMSG, no anti-bMCA antibodies could be detected in our assay system. In addition, no change in plasma levels of bMCA and PMSG compared with levels after the first injection was observed. Although it has to be confirmed by further experiments whether our findings can be generalized, the present results suggest that for repeated passive immunization in cattle homologous antibodies are to be preferred above heterologous antibodies.