Simple ELISA method for the evaluation of soluble HLA class I antigens in human serum

A simple sandwich ELISA method has been developed for the quantification of soluble HLA class I antigens (s-HLA) in human serum. The assay utilizes the monoclonal antibody Q6/64, directed to a monomorphic determinant of the HLA alpha-chain, to capture the antigen and the biotinylated NAMB1 monoclonal antibody, directed to beta 2-microglobulin, as the detection antibody. The extract of the LG-2 lymphoid cell line and pooled sera from 100 healthy subjects are utilized as standards. The arbitrary value of 100 s-HLA Relative Units/mL (RU/mL) is given to the 1:20 dilution of pooled human sera whose optical density value corresponds to the one of the extract of 1 x 10(6) LG-2 cells (6.25 micrograms/mL protein concentration). The assay is easy to perform, specific, reproducible (intra- and inter-assay variations ranging from 3.2% to 8.87%), sensitive (detection limit of 6 RU/mL), and needs a small amount of serum (0.1 mL). The mean serum levels of s-HLA found in 100 healthy normal subjects are 41.9 +/- 13.4 RU/mL. The potential uses of the method are discussed.