LY-96, also known as ESOP-1, is a protein which associates with toll-like receptor 4 on the cell surface and confers responsiveness to lipopolysaccyaride (LPS). LY-96 also cooperates with TLR2 in the response to cell wall components from Gram-positive and Gram-negative bacteria. It enhances TLR4-dependent activation of NF-kappa-B. ESOP-1 has 16 amino acids, the sequence of which shows 64% identity with human ESOP-1/MD-2. ESOP-1 mRNA is highly expressed in the mouse embryos at 7.5 days after coitus.