Lipopolysaccharide (LPS) Binding Protein (LBP) is a type 1 acute phase protein that is constitutively produced by the liver and rapidly upregulated during the acute phase response. LBP plays a central role in the response to LPS. The protein catalyses the monomerization of LPS and its transfer to (s)CD14 and to lipoproteins. In this way LBP has both a role in the activation pathway of LPS: activation of monocytes by LPS leading to release of inflammatory mediators and in the neutralization of LPS i.e. the uptake of LPS by lipoprotein and subsequent clearing. The assay can be used to quantify LBP in tissue culture supernatants of mouse cell cultures and in plasma and serum samples. In plasma of normal mice LBP is present at levels of approx. 6 µg/ml, which increase approx. 10-fold during acute phase responses.