Determination of Soluble CD14 Molecular Weight Variants in Human Plasma

Inflammation is an important underlying biochemical process of many fatal diseases and infections. Inflammation can be an acute response to trauma or infection, or chronic in cardiovascular diseases like atherosclerosis. In the United States, in 2011 atherosclerosis was responsible for 16% of all deaths, and in 2015 an estimated 200,000 people will die from sepsis [1, 2]. The Cardiovascular Health Study (CHS) found that elevated plasma concentration of the inflammatory protein soluble CD14 (sCD14) independently predicts mortality from atherosclerotic cardiovascular diseases in older adults [3]. Genomewide SNPs explained approximately 33% of the sCD14 phenotypic variance. In European Americans, the strongest genome-wide association signal was centered around the CD14 structural gene [3], yet little is known about how these SNPs affect the circulating plasma sCD14 that was measured by ELISA in this study. We therefore sought to determine if different forms of sCD14, as measured by the ELISA in the CHS, could be detected in a small (N=15), presumably healthy human population. Utilizing gel filtration column chromatography to estimate molecular weights (MWs), sCD14 was detectable over a spectrum of MWs from 20kDa to 150kDa, and had an approximate peak around 55kDa. These data support previous research suggesting that there are multiple forms of sCD14 in human plasma. It appears that the ELISA is not detecting sCD14 on microparticle or a 13kDa fragment (sCD14-ST). There does appear to be a higher MW sCD14 form that seems to be primarily detectable between 71kDa to 87kD. A sCD14 form in this MW range has never been described in the literature. In order to describe the different sCD14 MW variants, further inquiry is needed into the precise MWs of each form of sCD14 in plasma.