Granulocyte colony stimulating factor (GCSF) of Japanese flounder (Paralichthys olivaceus): Immunoregulatory property and anti-infectious function

Abstract

Granulocyte colony stimulating factor (GCSF) is a key regulator of neutrophil production, and plays a vital role in immune response of mammals and teleost against pathogen. Sequences of GCSF were identified in several teleost species, however, the function and activity of GCSF in teleost remain largely unknown. In this study, we examined the biological activity and the immunomodulatory property of a GCSF homologue, PoGCSF, from Japanese flounder (Paralichthys olivaceus). Structural analysis showed that PoGCSF possesses conserved structural characteristics of GCSF proteins, including a signal peptide and a typical IL-6 domain. The expression of PoGCSF was upregulated in a time-dependent manner by extracellular and intracellular bacterial pathogens and viral pathogen. Different expression patterns were exhibited in response to the infection of different types of microbial pathogens in different immune tissues. Recombinant PoGCSF increased the capability of host cells to defense against pathogen infection and enhanced the expression of immune related genes. The knockdown of PoGCSF attenuated the ability of host cells to eliminate pathogenic bacteria. In vivo results showed that overexpression of PoGCSF promoted the host defense against invading pathogenic microorganism. Collectively, this study is the first report about the immunoregulatory property and anti-infectious immunity of GCSF in teleost. These findings suggested that PoGCSF serves as an immune-related cytokine and plays an important role in the immune defense system of Japanese flounder.