Discovering TNF, TLRs, and other key components of the immune system
Quite early in my career, I isolated mouse TNF, a protein secreted by macrophages in response to lipopolysaccharide (LPS). I determined that TNF mediated many LPS effects, including systemic inflammation, shock, and death. My attention was thus drawn to the LPS receptor, which was responsible for alerting mammals to the presence of Gram(-) infection. My colleagues and I identified it as Toll-like receptor 4 by positional cloning, then a five-year undertaking. In so doing, we revealed an entire family of innate immune receptors that recognize molecular signatures of infection. This experience led me to create many other immunological phenotypes through random germline mutagenesis, and we tracked them down one by one. In recent years, my laboratory has developed automated meiotic mapping (AMM), which makes positional cloning an instantaneous procedure. Using AMM, we have positionally ascribed approximately 30,000 phenotypes to individual mutations: an accomplishment that only recently would have required thousands of years. This has allowed us to identify the majority of genes needed for robust immunity, and also has opened the door to a systematic search for disease modifier mutations.