Defective LPS signaling in C3H/HeJ and C57BL/10ScCr mice: Mutations in the Tlr4 gene.

Order of authorship in the original paper: Poltorak, Smirnova...Beutler. The authors, led by Beutler, showed that mice that harbor a mutation of the gene which codes for the production of the Toll-like receptor TLR4 quickly die of sepsis if challenged with a Gram-negative pathogen because they cannot sense the Lipopolysaccharides (LPS), also known as endotoxins, found in the outer membrane of Gram-negative bacteria, and, for that reason, cannot mount an adequate immune response. 

In 2011 the Nobel Prize in Physiology or Medicine 2011 was divided, one half jointly to Bruce A. Beutler and Jules A. Hoffmann "for their discoveries concerning the activation of innate immunity," and the other half to Ralph M. Steinman "for his discovery of the dendritic cell and its role in adaptive immunity."

(Thanks to Juan Weiss for this reference and its interpretation.)