The 2011 Nobel Prize in Physiology or Medicine was awarded to three researchers, including Jules Hoffman and Bruce Beutler, for their discoveries leading to the characterization of the Toll-like receptor (TLR) family of molecules. This family of molecules is encoded by genes in a wide variety of eukaryotes [yoo-KAR-ee-ohts], ranging from flies to humans, and plays an important role in which of the following processes?