Duck antibody responses to keyhole limpet haemocyanin, human immunoglobulin G and the trinitrophenyl hapten. Evidence of affinity maturation

Abstract

White Pekin ducks (three in each of four groups) received trinitrofluorobenzene (TNP) conjugated to keyhole limpet haemocyanin (KLH) or human immunoglobulin G (HIgG) either incorporated into adjuvants (complete Freund's adjuvant (CFA), then incomplete Freund's adjuvant (IFA) followed by intravenous (i.v.) injection) or by repeated i.v. injection. A rabbit received TNP-KLH with CFA, IFA, then i.v. Antibody (Ab) responses to the carrier proteins and to the TNP hapten were monitored by enzyme-linked immunosorbent assay (ELISA), optimized for use with duck Abs, and the response to TNP was also assessed in an ELISA designed to detect shifts in Ab affinity (Ka). The rabbit mounted good Ab responses to KLH and TNP, the Ka of the anti-TNP response increasing from 10^5.99 to 10^8.87 l/mol (758-fold) during the experiment. Ducks showed weak Ab responses to KLH and HIgG, with weakest responses among ducks receiving antigen by the i.v. route exclusively. The duck anti-TNP responses were vigorous in all cases. However, following i.v. administration of antigens (Ags), the anti-TNP responses were transient, being strong by 7 days but diminishing to background levels by 14 to 28 days after each inoculation. The duck Ab responses to TNP displayed affinity maturation. In ducks receiving Ags with adjuvants, Ka increased by levels comparable with or even exceeding those in the rabbit. Affinity increases were less, but nevertheless apparent, following i.v. administration of Ag. These results show that, contrary to expectation, the duck Ab response experiences affinity maturation. They also point to the transience of the duck Ab response to selected haptens/epitopes when Ag is not delivered in adjuvant. These findings have clinical implications for field responses to pathogens and vaccines.