MOLECULAR CHARACTERIZATION AND ADJUVANT EFFECT OF INTERLEUKIN-11 IN THE STREPTOCOCCOSIS FOMALIN-KILLED VACCINE OF THE NILE TILAPIA (Oreochromis niloticus)

Abstract

Interleukin-11 is an active signaling molecule in the host immune response to infection and the cytokine network. In this study, IL-11a and IL-11b were studied from the Nile tilapia (Oreochromis niloticus). The open reading frame of Nile tilapia IL-11a and IL-11b contained 717 and 603 bp, with a calculated molecular mass of 27.4 and 22.9 kDa, and a theoretical pI of 9.02 and 8.73, respectively. Both IL-11a and IL-11b consisted of a potential N-linked glycosylation site and a cysteine residue, and their genes are organized similarly, with 5 exons and 4 introns according to phylogenetic analysis, the IL-11a and IL-11b from Nile tilapia were categorically isolated from other IL-11 molecules and classified with those from other species. The tissue distribution of IL-11a in healthy fish was highly expression in spleen, liver, intestine and trunk kidney, while IL-11b showed higher expression levels in the spleen and tail. At 6 hours after infection by Streptococcus agalactiae, IL-11b was significantly up-regulated in the gills, intestines, spleen, and liver while IL-11a was significantly up-regulated at the same time but only in the spleen and liver. To provide new insights into the role of IL-11 in fish immune responses, a recombinant protein of IL-11 (rIL-11) was produced in bacterial system. In addition, IL-11a and IL-11b were up-regulated expression in Peripheral blood leukocytes (PBLs) by Lipopolysaccharides (LPS), Polyinosinic:polycytidylic acid (Poly I:C) and rIL-11 stimulation. Moreover, adjuvant effect of rIL-11 in the streptococcosis formalin-killed vaccine of the Nile tilapia was investigated. After the vaccination, the specific IgM antibody level of fish vaccinated with formalin killed cell (FKC) combined with rIL-11 was increased from 1 to 2 week post vaccinated and peak at 2 w.p.v. compared with control group (P

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