Vaccination Response of Young Foals to Keyhole Limpet Hemocyanin: Evidence of Effective Priming in the Presence of Maternal Antibodies

The ability to produce antibodies is essential for protection from infectious disease; however, in the neonate, maternal antibodies have been proposed to interfere with the foal's ability to respond to vaccination. In species other than the equid, keyhole limpet hemocyanin, a high-molecular weight protein, is used in vivo as an experimental vaccine component because of its high intrinsic immunogenicity. In this study, we show that young foals are able to produce a primary antibody response to vaccination at an early age. Thus, foals, like human infants, are capable of responding to antigenic exposure to a novel antigen (keyhole limpet hemocyanin) during the neonatal period. Although vaccinating foals in the presence of maternal antibodies failed to induce a primary serological response, priming occurred as comparable anamnestic responses were detected upon subsequent exposure to the antigen. There was no evidence of tolerance induction.