Humoral immunity to cholera toxin and ovalbumin in the brushtail possum (Trichosurus vulpecula)

AIM: To compare the humoral immune responses of female possums to ovalbumin (OVA) and cholera toxin (CT) administered using different routes and dosage regimes.

METHODS: Three groups of mature female possums were immunised intragastrically (n=15) or surgically (intraileal, n=4; Peyer`s patches, n=4). Levels of antibodies to OVA and CT in serum, ileal, vaginal, oviduct and uterine secretions were measured by indirect enzyme-linked immunosorbent assay (ELISA). All manipulations were conducted under general anaesthesia.

RESULTS: Antibodies to CT increased significantly in serum (p<0.001) and in lateral vaginal secretions (p<0.05) after intragastric immunisation using 250-1000 g CT. Simultaneous intragastric administration of CT with 3 mg OVA did not significantly increase antibody levels to OVA. When OVA (3 mg) and CT (250 g) were injected into the ileum, followed by intragastric administration 4 weeks later, antibody levels to CT were significantly (p<0.05) increased in serum, uterine and medial vaginal secretions, and antibody levels to OVA were significantly (p<0.05) increased in serum and medial vaginal secretions. When OVA (3 mg) with Incomplete Freund`s adjuvant was injected directly into Peyer`s patches, followed by peritoneal administration 4 weeks later, antibody levels in serum, ileal and reproductive-tract secretions were generally higher than those that resulted from the other immunisation treatments.

CONCLUSIONS: Administration of OVA induced an antibody response in serum and in reproductive and alimentary tract secretions when administered with CT directly into the ileum, or when injected into Peyer`s patches and peritoneum. CT was a potent enteric immunogen.

KEY WORDS: Possum, cholera toxin, ovalbumin, intragastric immunisation, Peyer`s patches, mucosal immunity, antibody.