Characterization and Expression Analysis of B Cell Receptor Accessory Molecule CD79 Gene in Humphead Snapper (Lutjanus sanguineus)

CD79, a key component of the B cell antigen receptor complex, is composed of CD79 alpha(Ig alpha) and CD79 beta(Ig beta) encoded by mb-1 and B29 respectively, and plays an important role in B cell signaling. In this study, we isolated and characterized mb-1 and B29 from humphead snapper (Lutjanus sanguineus). Their tissue distribution and expression profiles after stimulations in vitro and in vivo were also investigated. The humphead snapper mb-1 and B29 contain open reading frames of 684 bp and 606 bp, encoding 227 amino acids and 201 amino acids, respectively. Both CD79 alpha and CD79 beta possess signal peptide, extracellular Ig domain, transmembrane region and immunoreceptor tyrosine kinase activation motif (ITAM). Mb-1 is highly expressed in lymphoid organs (thymus, posterior kidney and spleen) and mucosal-associated lymphoid tissues (gill and intestine), while B29 is mainly detected in posterior kidney, spleen, gill and skin. Furthermore, transcription of mb-1 and B29 in head kidney leucocytes was up-regulated following lipopolysaccharide (LPS), pokeweed mitogen (PWM), and polyinosinic-polycytidylic acid (PolyI:C) stimulation, respectively, and their expression level in anterior kidney and spleen was also increased after challenged with formalin-inactived Vibrio harveyi. These results indicated that humphead snapper CD79 molecule might play an important role in immune response to pathogen infection.