A novel CC chemokine gene was isolated from large yellow croaker (Pseudosciaena crocea) by expressed sequence tag (EST) analysis (LycCC). The open reading frame (ORF) of 300 nucleotides (nt) of LycCC encodes a polypeptide of 100 amino acids (aa), including a 22-aa signal peptide and a 78-aa mature polypeptide. The deduced LycCC possesses the typical arrangement of four cysteines as found in other known CC chemokines (C(27) C(28), C(55) and C(77)). Genomic analysis revealed that LycCC gene, spanning 2259 nt, consisted of three exons and two introns. Recombinant LycCC (rLycCC) protein produced in Pichia pastoris exhibited marked chemotactic activity for peripheral blood leucocytes (PBLs) from large yellow croaker. RT-PCR analysis showed that LycCC gene was constitutively expressed in all nine tissues examined, although at a different level. Upon stimulation with poly(I:C) or inactivated trivalent bacterial vaccine, LycCC gene expression was obviously up-regulated in kidney, gills, spleen, liver, intestine, blood and heart at 12h post-induction, and poly(I:C) was more potent than bacterial vaccine in up-regulating LycCC expression. Time-course analysis using a real time PCR revealed that LycCC transcripts in spleen and kidney were quickly increased by either poly(I:C) or bacterial vaccine and reached their peak levels at 12h, followed by a rapid decrease at 24h. An in vivo administration of rLycCC could significantly up-regulate the expression of low molecular mass polypeptide 10 (LMP10), MHC class I alpha chain and beta(2)-microglobulin (beta(2)m) in spleen, kidney and blood at 24h after treatment. These results suggest that LycCC may not only have a pro-inflammatory function in immune response triggered by poly(I:C) or bacterial vaccine, but also be involved in adaptive immune response by modulating MHC class I antigen processing and presenting pathway in large yellow croaker.