Use of a lipid-emulsion carrier for immunisation of dab (Limanda limanda) by bath and oral routes: an assessment of systemic and mucosal antibody responses

The ability of a novel fish-oil emulsion antigen-delivery system administer ed orally and by immersion, to stimulate antibody responses in the dab was measured. In addition, the kinetics of antibody secreting cell (ASC) respon ses were monitored by ELISPOT in single cell suspensions derived from perfu sed gill filaments,,out mucosa, peripheral blood leucocytes (PBL) and head kidney to investigate if the mucosal (gill and gut) and systemic (PBL and h ead kidney) compartments responded in a linked or independent manner. Oral intubation of human gamma globulin (HGG) (25 mg) in saline induced no detec table responses. Immersion in a bath containing HGG in lipid emulsion induc ed a transient ASC response in the blood only. Anal intubation of HGG (25 m g) in saline induced a slight response in the gut and blood. Oral intubatio n of HGG (25 mg) in lipid emulsion induced ASC responses in the gut from we eks 2 to 10 post-immunisation and transiently in the gill (week 2 only) but no response (above background) in the head kidney. None of the above metho ds of immunisation induced serum antibody titres. Intraperitoneal injection of HGG (1 mg) in saline induced high numbers of ASC in the head kidney, gu t and gill as well as serum antibody. The ASC response in the head kidney w as detected from weeks 5 to 10, peaking at week 5. The response in the gill was from weeks 3 to 10, peaking at week 6, and the response in the gut was from weeks 5 to 10 peaking at week 8. The numbers of ASC in gut and gill f ollowing i.p. immunisation were larger than after oral-in-lipid administrat ion, but the latter induced a more rapid response. The results indicate tha t systemic stimulation (i.p. injection) induced ASC responses in both syste mic and mucosal compartments. The orally protected HGG in lipid emulsion wa s more effective than oral HGG in saline and anal HGG in saline in inducing ASC responses in the gut and the gill suggesting that oral immunisation ca n induce a common mucosal response independently of the head kidney. (C) 20 00 Elsevier Science B.V. All rights reserved.