A novel teleost C1q C chain (PoC1qC) participates in complement and leukocytes antibacterial immunity

Abstract

Complement C1q composed of C1q A, B, C chains is the initial vital protein of classical complement pathway, playing an essential role in innate immune response. Whereas in teleost, the immune roles of C1q C chain are largely scarce. In this research, we studied the complement/peripheral blood leukocytes (PBLs) activation and antibacterial potentials mediated by Japanese flounder (Paralichthys olivaceus) C1q C chain (PoC1qC). The PoC1qC shares 56.7%–87.6% identities with that of teleost and mammals. The expression of PoC1qC can be detected in various organs, notably up-regulated by V. harveyi stimulation, and down-regulated by E. tarda infection. The recombinant PoC1qC (rPoC1qC) could directly bind to different bacteria and exhibit antibacterial potential. Consistently, rPoC1qC and anti-rPoC1qC antibody could remarkably enhance or suppress the complement hemolytic and bactericidal activity, respectively. Furthermore, rPoC1qC could directly interact with PBLs, resulting in the activation of proliferation, chemotaxis, and phagocytosis of PBLs, and the generation of ROS/acid phosphatase activity of PBLs. Lastly, we found in vivo rPoC1qC could promote the host to resistant microbial invasion. Taken together, our findings provide the first evidence that PoC1qC played pivotal roles in complement and PBLs activation and antibacterial activity.