A CD83-like molecule in sea bass (Dicentrarchus labrax): molecular characterization and modulation by viral and bacterial infection.

The CD83 cell surface marker is an important and intriguing component of immune system. It is considered the best marker for mature human dendritic cells, but it is also important for thymic development of T cells, and it also plays a role as a regulator of peripheral B-cell function and homeostasis. A CD83-like molecule was identified in sea bass (Dicentrarchus labrax) by EST sequencing of a thymus cDNA library; the CD83 cDNA is composed of 816 bp and the mature CD83 peptide consists of 195 amino acids, with a putative signal peptide of 18 amino acids and two possible N-glycosylation sites. The comparison of sea bass CD83 sequence with its homologues in other fish species and mammals shows some differences, with two cysteine residues conserved from fish to mammals and a high variability both in the total number of cysteines and in mature CD83 sequence polypeptide length. Basal transcripts levels of CD83 mRNA are highest in liver, followed by thymus. The in vitro treatment of head kidney leukocytes with LPS resulted in a down-regulation on CD83 mRNA leves both after 4 and 24 h, whereas with poly I:C an up-regulation after 4h followed by a down-regulation at 24 h was observed. An in vivo infection of sea bass juveniles with nodavirus induced an increase of CD83 expression on head kidney leukocytes both after 6 and 24 h and a decrease after 72 h. On the other hand, an in vivo infection with Photobacterium damselae bacteria induced a decrease of CD83 transcript levels after 6 and 24 h and an increase after 72 h. These findings suggest in sea bass CD83 expression could be modulated by viral and bacterial immune response.