Decay-accelerating factor (DAF/CD55) is a functional active element of the LPS receptor complex

Previously, we identified an 80 kDa membrane protein (LMP80) that is capable of binding to LPS and lipid A in the presence of LBP and sCD14. LMP80 could also be detected after immuno-coprecipitation of cell membranes with LPS and lipid A, indicating a physical contact of LMP80 and LPS/lipid A. Further analysis and peptide sequencing revealed that LMP80 is identical to CD55 (decay accelerating factor, DAF), a regulatory molecule of the complement cascade. Transfection of LPS-hyporesponsive Chinese hamster ovary (CHO) cells with human CD55 resulted in the translocation of NF-kappaB upon stimulation with LPS or lipid A. Our results demonstrate a new functional role of CD55 as a molecule able to mediate LPS-induced activation of cells that may be part of a multimeric LPS receptor complex.