Identification and expression profiles of granzyme genes in immune response from Nile tilapia (Oreochromis niloticus)

Abstract

Granzymes (Gzms) are crucial cytotoxic molecules involved in cell-mediated immunity in mammals. However, their roles in teleost fish, such as Nile tilapia, were less understood. In this study, we focused on the identification of granzyme genes (OnGzms) from Nile tilapia (Oreochromis niloticus) and the potential functions in anti-infectious immunity, as well as their expression patterns in response to interleukin-2 stimulation. Eleven Gzm genes were identified in tilapia, including GzmA-1, GzmA-2, GzmK, GzmB-1, GzmB-2, GzmB-3, GzmH-1, GzmH-2, GzmG, GzmF, and GzmE, which contain conserved serine protease active sites. OnGzms were categorized into four groups through homology analysis at a shared locus. Gene replication processes, such as whole-genome replication specific to teleost and unequal crossing over of tandem genes, may lead to multigene copies of OnGzm genes. It appeared that the vertebrate GzmA/K originated from a common ancestor in terms of evolution. After Streptococcus agalactiae, Aeromonas hydrophila, Edwardsiella piscicida and Poly (I:C) challenges, expression of OnGzms was significantly up-regulated only in response to E. piscicida (an intracellular bacterium) infection, indicating potential functions of OnGzms involving in combating intracellular infection by the bacterium E. piscicida. Stimulation with rOnIL-2 led to increased expression of OnGzms in leukocytes, suggesting involvement in cell-mediated cytotoxicity. These findings enriched the knowledge of potential roles in resisting E. piscicida intracellular infection of granzyme genes in teleost fish.