Enteric coated microspheres as an oral method for antigen delivery to salmonids

Abstract

A comparative study was conducted to determine the immunisation efficacy of enteric coated antigen microspheres (ECAMs) versus intraperitoneal (i.p.) and immersion antigen delivery. Anal intubation of antigen served as a positive control by directly delivering the antigen to the hindgut. Naive juvenile coho salmon Oncorhynchus kisutch were exposed to three different concentrations of trinitrophenylated lipopolysaccharide (TNP-LPS) or trinitrophenylated keyhole limpet haemocyanin (TNP-KLH) by the three routes, oral (ECAM), intraperitoneal, immersion or anal intubation. TNP-LPS or TNP-KLH were prepared for oral immunisation by coating onto 0·45 mm dextrose sugar beads followed by an application of Eurdragit LD-30 co-polymer. Serum was taken from immunised and non-immunised control fish fed diet containing nonantigen coated beads. The serum was assayed by ELISA at 4, 6 and 8 weeks post-immunisation to assess anti-TNP antibody titres. Statistical analysis of the serum showed that oral vaccination significantly increased anti-TNP titres at 4 and 6 weeks post-vaccination as compared with the controls (P<0·05). The anti-TNP titres after TNP-LPS i.p. immunisation were significantly higher than the controls (P<0·05) at 4, 6 and 8 weeks post immunisation, while the group that was immersed showed no significant difference from the control. There was no significant difference between TNP-LPS i.p. and ECAM immunisation methods.The TNP-KLH immunised ECAM group showed significantly elevated levels of anti-TNP antibodies compared with controls at 6 and 8 weeks, while the i.p. immunised group was significantly higher than the control throughout the 8-week period. The group immunised by anal intubation had significantly higher titres than controls at 6 and 8 weeks but not at 4 weeks.