DAO 32:195-200 (1998)  -  doi:10.3354/dao032195

A lethal effect of rainbow trout Oncorhynchus mykiss plasma containing intact complement factors on Gyrodactylus derjavini was demonstrated. It was associated with binding of complement factor C3 to certain carbohydrate-rich parasite structures. Parasites were exposed in vitro to plasma from rainbow trout. Untreated plasma from infected and uninfected fish showed lethal effects on the parasites within 1 h, whereas prior heat inactivation of complement prevented any parasite killing. Inhibition of the classical pathway by EGTA (ethyleneglycol-tetraacetic acid) treatment of plasma did not prevent the killing. It was shown by immuno-cytochemical assays that C3 bound directly to certain parasite structures (cephalic gland openings, parasite body, hamulus sheath). In contrast, no immunoglobulin binding was detected on the parasites. Lectin-binding assays indicated mannose-rich regions in the cephalic gland openings and lactose derivatives in the hamulus sheath. Galactose derivatives showed a general distribution in the glycocalyx. Thus, the antibody-independent plasma effect on the gyrodactylids are ascribed to the alternative complement pathway, and it is suggested that some carbohydrate epitopes on the parasites are involved in the C3 activation.

Rainbow trout · Oncorhynchus mykiss · Gyrodactylus · Complement · Immunoglobulin · Glycobiology · Carbohydrate · Lectins