Abstract
The protective immune response in zebrafish (Danio rerio) against the parasitic ciliate Ichthyophthirius multifiliis, targeting host skin, fins and gills, comprises an accelerated and manifold elevated immunoglobulin gene expression as well as a significantly elevated number of neutrophils at infected sites. Experimental fish were subjected to a primary I. multifiliis infection followed by a series of secondary exposures before they were challenged by a high dosage of infective theronts. Immunized fish responded immediately with a protective response suggesting existence of immunological memory whereas fish exposed to the parasite for the first time obtained a marked infection. The primary response to infection was dominated by expression of genes encoding acute phase reactants and inflammatory cytokines as well as recruitment of neutrophils at infected locations. Immunized fish showed a significantly upregulated immunoglobulin gene expression following challenge, which indicates existence of a secondary response effected by antibodies. Both responses induced a significantly elevated expression of the Th2 signature cytokine Il13. The increased presence of neutrophils in immunized fish suggests that innate cell mediated immunity supplements or influence the protective response against the parasite.
Highlights
Teleost fishes are equipped with well-developed immune systems comprising both innate [1, 2] and adaptive responses [3], which is the basis for existence of successful vaccination programs in the aquaculture sector [4,5,6]
We investigated a range of cytokines to elucidate the gene expression profile of the primary and the protective response in relation to the Th pathways, which are known in mammals
We showed a significant up-regulation of ighz in fins of in protected fish (IC) fish suggesting occurrence of an antibody mediated protective response, which complies with earlier observations in rainbow trout, where the mucosal antibody IgT [57] plays a major role in protection against I. multifiliis [19, 21, 22]
Summary
Teleost fishes are equipped with well-developed immune systems comprising both innate [1, 2] and adaptive responses [3], which is the basis for existence of successful vaccination programs in the aquaculture sector [4,5,6]. A protective immune response can be induced in fish by various forms of immunization it is still inadequately described to what extent teleosts mount a secondary immune response following re-stimulation. A classical secondary immune response as described in mammals is characterized by immunological memory and an accelerated and manifold rise of specific antibodies with a partial switch of Ig class [7]. Fish do not display a class switch [8] but may exhibit a re-inforced antibody production relatively few studies have elucidated this process.
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