Molecular cloning, characterization and tissue expression of CD4 in Chinese goose.

CD4 protein is a single chain transmembrane glycoprotein belonging to the immunoglobulin superfamily that recognizes the major histocompatibility complex (MHC) class II molecules. It plays an important role in cell-mediated immunity. Here, the full-length cDNA of CD4 in Chinese goose (Anser cygnoides) was cloned and identified. The goose CD4 is 1940bp in length and encodes a single open-reading frame of 480 amino acids. The putative amino acid sequence of goose CD4 consisted of a signal peptide, four potential N-glycosylation sites, a transmembrane region and a cytoplasmic tail. The multiple sequence alignment and phylogenetic analysis suggested that goose CD4 shared a higher similarity with avian than other vertebrates. Semi-quantitative RT-PCR analysis showed that the highest level of CD4 mRNA transcripts was presented in the thymus, and relatively lower in the spleen, small intestine, brain and trachea. Low expression was seen in the bursa of fabricius, cecal tonsil, cecum, skin, lung, kidney and liver. In gosling, the CD4 transcript was expressed with high abundance in the thymus, and relatively lower in the spleen, cecal tonsil and small intestine. However, in adult goose, high expression was seen in the thymus, spleen and cecum, and relatively lower in the cecal tonsil and small intestine. During the course of NGVEV infection, the obvious increase in CD4 gene expression was observed in the spleen, bursa of fabricius and harderian gland. Interestingly, a notable decrease in CD4 mRNA expression in the small intestine at 5d PI and followed by an increase of that at 19d PI were shown.