Identification of the 80-kDa LPS-binding protein (LMP80) as decay-accelerating factor (DAF, CD55).

The activation of immunocompetent cells by lipopolysaccharide (LPS) during severe Gram-negative infections is responsible for the pathophysiological reactions, possibly resulting in the clinical picture of sepsis. Monocytes recognize LPS mainly through the LPS receptor CD14, however, other cellular binding structures have been assumed to exist. In previous studies, we have described an 80-kDa LPS-binding membrane protein (LMP80), which is present on human monocytes as well as endothelial cells. Here we demonstrate that LMP80 is widely distributed and that it forms complexes together with LPS and sCD14. Furthermore, we report on the biochemical purification of LMP80 and its identification as decay-accelerating factor, CD55, by amino acid sequencing and cloning techniques. Our results imply a new feature of CD55 as a molecule which interacts with LPS/sCD14 complexes. However, the involvement of CD55 in LPS-induced signaling remains to be elucidated.