The MTS510 antibody reacts with the molecular complex of Toll-Like Receptor 4 and MD-2 (TLR4-MD-2) which is expressed on LPS responsive macrophages. TLR4, a member of the Toll-Like Receptor Family, has been renamed as CD284 and identified to be the transmembrane signal-transducing portion of the receptor for LPS. TLR4 associates on the cell surface with CD14 and MD-2, a 0.7 kDa molecule which is anchored to the membrane via its physical association with TLR4. The association of MD-2 with TLR4 is required for recognition of LPS and the anti-mitotic compound Taxol, which mimics the action of LPS on mouse cells. MTS510 mAb detects TLR4-MD-2 on the surface of thioglycollate-elicited macrophages from all mouse strains tested (ie, BALB/c, C57BL/6, C3H/HeJ, C3H/HeN, and DBA/1), including the C3H/HeJ strain which expresses an LPS-resistant mutant TLR4. Expression of TLR4-MD-2 is down-regulated on peritoneal macrophages after exposure to LPS, correlating with the occurrence of LPS tolerance. TLR4-MD-2 is not detected on splenocytes or thymocytes.