Humoral immune response of carp (Cyprinus carpio) induced by oral immunization with liposome-entrapped antigen

To study the value of liposomes as carriers of antigens for oral vaccination in fish, humoral immune responses were analyzed after immunizing carp (Cyprinus carpio) with liposome-entrapped bovine serum albumin (BSA) as a model antigen. Oral immunization of BSA (100 mug)-containing liposomes that were stable in carp bile induced significant antibody responses against BSA in serum as well as in intestinal mucus and bile. By contrast, no serum antibody responses were observed when fish were orally immunized with the same dose of BSA-containing unstable liposomes or BSA alone. BSA-specific antibody-secreting lymphocytes were detected in the spleen and head kidney of immunized fish. Furthermore, when we applied Vibrio cholerae toxin B subunit (CT-B)-conjugated liposomes containing BSA for oral immunization we found significant increases of anti-BSA antibodies in serum. Our results suggest that delivery systems using liposomes or liposomes with CT-B to the intestinal tract are essential for inducing effective humoral immune responses following oral vaccination. (C) 2003 Elsevier Science Ltd. All rights reserved.