Passive immunization of channel catfish Ictalurus punctatus with anti-Flavobacterium columnare sera

Passive immunization of channel catfish Ictalurus punctatus (Rafinesque) was conducted to determine if anti-Flavobacterium columnare serum was protective when injected intraperitoneally (i.p.) into channel catfish. The anti-F. columnare serum was produced by actively immunizing (i.p. injection) channel catfish with sonicated whole cells or purified lipopolysaccharide (LPS) of F. columnare in Freund's adjuvant. Serum anti-F. columnare activity was verified by Western blotting and ELISA of serum. Normal serum and sterile culture broth were used as controls. Complement was inactivated in all sera by heating. After 48 h, passively immunized fish were challenged with virulent F. columnare by i.p. injection. A group of unchallenged fish served as controls. The immune response of catfish to the antigenic fractions was different when examined by Western blotting. Antibody produced with whole-cell antigen responded to a broad range of molecular weight components, while LPS antigens were restricted to a pair of bands near 20 kDa. Control fish injected with culture medium experienced 100% mortality 14 d post-challenge. Relative percent survival was 77 and 73 for catfish passively immunized with anti-LPS and anti-whole-cell serum, respectively. Results suggest that antibodies in the serum are involved in the protective immune response against columnaris disease in channel catfish.