First characterization of fish CD22: An inhibitory role in the activation of peripheral blood leukocytes

In mammals, CD22 is a member of the Ig superfamily that serves as an inhibitor during B cell responses to foreign antigens. In this study, we characterized for the first time a fish CD22 from tongue sole Cynoglossus semilaevis (CsCD22). CsCD22 possesses the conserved structural features of CD22 and shares 35%-54% sequence identities with other fish CD22. mRNA expression of CsCD22 was most abundant in head kidney and heart. CsCD22 protein was detected on the surface of peripheral blood leukocytes (PBL). In the presence of rCsCD22 antibody, the proliferation, phagocytosis, and antibacterial activity of PBL were significantly increased. These results indicate for the first time that fish CD22 plays an inhibitory role in PBL activation.