Immune system produces many different proteins to protect us from microbial infections. The immune proteins are also prepared by biotechnology companies through by culturing them in a bacterial or human cell cultures. Both the bacterial and human cell cultures have the capacity of producing same polypeptide from the same mRNA (messenger ribonucleic acid) molecule.
The proteins that are isolated from the bacterial cultures are often inactive. To become functional or active, many proteins undergo post-translational modifications. The proteins produced from human cell culture system undergo post-translational modifications and the proteins isolated from them are active.