Natural and Acquired Agglutinins toAeromonas hydrophilain Carp (Cyprinus carpio)

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Abstract
Formalin-killed Aeromonas hydrophila cells (F-Ah) and heat-inactivated and fragmented A. hydrophila cells (H-Ah) both evoked agglutinin titers in carp (Cyprinus carpio) at 21 °C, which persisted for at least 8 mo. The height of the agglutinin response depended on the antigen dose and bacterin. H-Ah injection induced the highest agglutinin production. The peak day of the response was dependent not on antigen dose, but on bacterin type (day 14 and 20 for H-Ah and F-Ah, respectively). Antisera raised against the two bacterins differed in agglutinating properties. F-Ah induced agglutinins which were mainly directed to A. hydrophila lipopolysaccharide (LPS), whereas H-Ah induced activity against other bacterial antigens. Sephadex G200 fractionation of immune (anti F-Ah) and non-immune sera resulted in four and three protein peaks, respectively. The peak of immunoglobulin (Ig) coincided with the first protein peak. ln immune serum, the first peak agglutinated both F-Ah and H-Ah, but the third peak contained only H-Ah agglutinating activity. In non-immune serum, only fractions of the second and third peak showed some agglutination with H-Ah predominantly.