He left medical research and went to work for a biotech firm, where he led a research and development group looking at diagnostic agents for auto-immune disease. His former mentor saw the work he was doing and persuaded Chen to pursue a Ph.D. in the United States. Chen applied to work in the lab of Kelsoe, then at the University of Maryland at Baltimore, because of Kelsoe's work in dissecting how the normal immune system responds. Learning how the normal immune system responds would give him insight into what goes wrong in instances of auto-immunity. When Kelsoe came to Duke, Chen went with him.
Complement recognizes bacteria and viruses even before an antibody is formed.
Chen discovered that complement, rather than being the cause of auto-immune disease as was commonly thought, actually protects the immune system. When disease is at the height of its activity, the complement level can go very, very low. Because complement was blamed for the disease, no one thought to replace the complement. Now we are trying to replace complement to fight the disease. Chen gives credit to his teachers and mentors along the way.