V. All rights reserved. Toll-like receptors (TLRs) take part in both the innate and adaptive immune systems. The role of the transmembrane domain in TLR signaling is still elusive, while its importance for the TLR activation was clearly demonstrated. In the present study the ability of the TLR3 transmembrane domain to form dimers and trimers in detergent micelles was shown by solution NMR spectroscopy. Spatial structures and free energy magnitudes were determined for the TLR3 transmembrane domain in dimeric and trimeric states, and two possible surfaces that may be used for the helix-helix interaction by the full-length TLR3 were revealed. Structured summary of protein interactions TLR3-TM and TLR3-TM bind by nuclear magnetic resonance. 2014 Federation of European Biochemical Societies.