DEVELOPMENT OF AN ELISA FOR QUANTIFICATION OF HUMAN PROTEIN-S IN CELL-CULTURE FLUIDS USING COMMERCIAL POLYCLONAL ANTISERA

An enzyme-linked immunosorbent assay (ELISA) was developed to measure protein S antigen released into cell culture fluids. We used readily a vailable commercial polyclonal antisera to develop the assay. This ass ay was sensitive with a detection limit of about 0.086 ng/ml. Between- assay precision (coefficient of variation) at levels of 0.2, 1.1, and 13.9 ng/ml was 14%, 15%, and 11% respectively. Specificity and accurac y wars demonstrated from the use of: 1) culture fluids from 3-primary endothelial cell cultures and 7-cell lines known to constitutively pro duce protein S; 2) 2-cell lines not synthesizing protein S; and 3) fro m selected samples of normal and protein S deficient plasma. The ELISA described here was about 12-fold more sensitive and 40-fold more cost affective when compared to a commercial ELISA kit. Thus the assay pro vided a sensitive, specific, precise and economical method useful for the measurement of the nanogram amounts of protein S commonly encounte red in cell culture fluids.