The bacterial expression in a bacterial expression system, E. coli (E. coli) is the most widely used, the genetic background is relatively clear, having a safe use, simple operation, substantial expression of the exogenous gene expression system. E. coli expression system to express the non-glycosylated antibody molecules including scFvs, including. Compared with the mammalian cell lines, E. coli expression system is more rapid and easy access to express the antibody, and therefore suitable for large-scale screening and antibody production. Further, using E. coli expression system can obtain a high concentration of polyclonal antibody (RAB), and have reported that the expression level of up to 2 g / L. However, E. coli are not suitable for the expression of glycosylated protein, so to express glycosylated proteins, such as scFv-Fc fusion proteins, the need to select the other expression systems. E. coli expression system for the expression of the different active rAbs exist different expression site, including secreted into the extracellular periplasmic space, the outer membrane or the internal and cytoplasm. Use of a promoter such as lac, trp and tac induce antibody expression, these promoters can be lac obstructions regulation and isopropyl-β-galactosidase (IPTG) induction.