A single C1q A chain promotes leukocytes phagocytosis/chemotaxis and mediates bacterial clearance in Japanese flounder Paralichthys olivaceus

Abstract

Complement component 1q (C1q) is the first component involved in the activation of complement classical pathway and acts as a linker of the innate and adaptive immune system. The C1q is a macromolecular containing three chains i.e. C1q A, C1q B, and C1q C. In teleost, the biological functions of C1q A chain is still unclear. In this study, we investigated the immunological properties of a C1q A chain from Japanese flounder (Paralichthys olivaceus) (PoC1qA). PoC1qA containing the conserved CLR and C1q domain, shares 45.4%–78.6% identities with that of other teleost and mammals. PoC1qA expression pattern was constitutive in tissues, with higher expression in spleen and liver. Besides, the PoC1qA expression was notably regulated by pathogenic invasion. In vitro the recombinant PoC1qA (rPoC1qA) could directly bind a variety of bacteria, and affect bacterial growth and survival. Moreover, PoC1qA could influence the hemolysis and bactericidal activity of fish serum. Additionally, rPoC1qA could interact with the membrane of peripheral blood leucocytes (PBLs), promoting the PBLs phagocytosis and chemotaxis, and enhancing the activation of PBLs. Consistently, in vivo rPoC1qA could restrain the bacterial replication in immune tissues. To sum up, our observations added the first evidence that an A chain of teleost C1q plays vital roles in mediating PBLs activity and antibacterial immunity.