Molecular cloning and expression analysis of CCL25 and its receptor CCR9s from Epinephelus coioides post Cryptocaryon irritans infection

Among other functions, CCL25/CCR9 has an important role in regulating the trafficking of developing T cells in the thymus, and in homing memory T cells to the small intestine. The function of this chemokine-receptor complex is not well studied in fish. We identified a CCL25-like (EcCCL25, 108 aa) and two CCR9-like sequences (EcCCR9aa 373 aa; and EcCCR9b, 375 aa) from a transcriptome database of orange-spotted grouper (Epinephelus coioides). EcCCL25, EcCCR9a, and EcCCR9b shared conserved structural features with homologs from mammals and from other fish, and a consistent relationship with phylogenetic trees and sequence identities. In healthy grouper, EcCCL25, EcCCR9a, and EcCCR9b were highly expressed in the thymus, and the gills, were expressed at lower levels in the stomach, and had different expression levels in other tissues. After infection with Cryptocaryon irritans, EcCCL25 expression was up-regulated at early time points in the spleen and head kidney, and in the skin, and gills at later time points; EcCCR9a expression was increased in the gill, spleen, and head kidney. After infection with C. irritans, EcCCR9b expression was reduced in all tissues tested. These results suggested that grouper CCL25/CCR9a complex may be involved in host defense against C. irritans infection.