C3 and bacterial infectious disease: One limitation of this study is that we only focused on the gene expression of certain genes, which may omit other important molecules, especially lysozyme and complement component 3 which might partially contribute to survival; moreover, antimicrobial peptides, c-reactive protein, protease inhibitors, pentraxins, and transferrin (71), which are also known to participate in the defense of bacterial infection, should be further investigated.