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 dosag e regimes. METHODS: Three groups of mature female possums were immunised intragastrica lly (n=15) or surgically (intraileal, n=4; Peyer's patches, n=4). Levels of antibodies to OVA and CT in serum, ilea, vaginal, oviduct and uterine secr etions 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 mug CT. Simultaneous intragastric administration of CT with 3 mg O VA did not significantly increase antibody levels to OVA. When OVA (3 mg) a nd CT (250 mug) were injected into the ileum, followed by intragastric admi nistration 4 weeks later, antibody Levels to CT were significantly (p<0.05) increased in serum, uterine and medial vagina secretions, and antibody lev els to OVA were significantly (p<0.05) increased in serum and medial vagina l secretions. When OVA (3 mg) with Incomplete Freund's adjuvant was injecte d directly into Peyer's patches, followed by peritonea administration 4 wee ks later, antibody levels in serum, ilea 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 an d in reproductive and alimentary tract secretions when administered with CT directly into the ileum, or when injected into Peyer's patches and periton eum. CT was a potent enteric immunogen.