Sequence alignment of the intracellular signaling domains of representative members of TLR/IL-1 receptor family. Conserved residues are boxed, with identical amino acids shaded in dark gray and similar amino acids shaded in light gray. The COOH-terminal region that is indispensable for TLR- and IL-1–mediated signaling is underlined. The proline residue that is conserved among eight of the nine human TLRs, which is critical for signaling induced by TLR2 and TLR4, is marked with a triangle.