The
infection of carp and other cyprinid fish with Trypanosoma danilewskyi was reported to cause significant morbidity and mortality in aquaculture.
Tubulin is a component of parasite excretory/secretory (ES) products recognized by
antibodies present in the serum of recovered hosts. To assess the role of parasite
tubulin in the induction of a protective immune response in the goldfish, recombinant T. danilewskyi
beta-tubulin was produced in Escherichia coli and used to immunize goldfish against challenge with live parasites. Affinity purified rabbit anti-recombinant
tubulin IgG bound to both surface and internal structures of trypanosomes, and when added to parasite cultures caused a dose-dependent inhibition of their growth in vitro. Immunization of goldfish i.p. with either 40 microg or 80 microg of
endotoxin-free beta-tubulin+Freund's complete adjuvant (FCA) caused a significant decrease in
parasitemia during the establishment phase of the
infection (days 3 and 7) and increased the time required to reach the maximal mean number of parasites compared to non-immunized
sham-injected control fish. The serum from immune fish contained
antibodies that recognized trypanosomes as determined by confocal immunofluorescence microscopy and specific
antibodies that recognized recombinant
tubulin as measured by ELISA. Thus, the immunization of goldfish with recombinant parasite
beta-tubulin conferred partial antibody-mediated protection against a challenge
infection with live trypanosomes. This is a first report that parasite
tubulin is immunogenic in poikilothermic vertebrates.