“We discovered one of the key proteins required for innate immune sensing using a pure genetic approach.”

The Toll-like receptor (TLR) field has undergone a rapid expansion since it was recognized in 1998 that these proteins serve as the key sensors of microbial infection of all types. Attention then turned to the adaptor proteins that permit signaling from the TLRs. Our paper describes the use of random germline mutagenesis in the mouse to identify one such adaptor, known as TRIF, as the basis of MyD88-independent TLR signaling. The paper filled a major gap in the field, in that it had not been known which adaptor(s) were responsible for signaling that occurred in the absence of MyD88. It also showed the power of germline mutagenesis in addressing questions of this type. Finally, ours was the first paper to show that TLR signaling is important in the containment of viral infections (in the example, mouse cytomegalovirus infection).

The highly focused screen that we pursued to identify an ENU-induced mutation that affected TIR domain signaling would certainly be useful to others, and since the publication of this paper, other mutations that affect innate immune sensing have been identified in our own laboratory. The identification of the molecular basis of MyD88-independent signaling is equivalent to the discovery of about half of all signals induced by lipopolysaccharide (LPS). Notably, we also discovered that the immuno-adjuvant effect of LPS is mediated by the TRIF signaling pathway: something that may be very important in vaccine development.

We discovered one of the key proteins required for innate immune sensing using a pure genetic approach. We showed that without this protein, animals are vulnerable to both bacterial and viral infections. The protein is among the most important molecular components of the innate immune system.

Our laboratory originally demonstrated that the mammalian TLRs act as microbial sensors [(Poltorak, et al, Science, 282: 2085-2088 (1998)]. This earlier discovery, like the present one, was achieved by a forward genetic approach (positional cloning). In the wake of this work, our laboratory focused on the use of ENU mutagenesis in the mouse to disclose other innate immune deficiency mutations. This was a major example of the utility of the approach.