Development of an enzyme immunoassay for the quantitation of cellular antigen expression.

An enzyme immunoassay is described which can be used to quantitate the cellular expression of antigens recognised by mouse monoclonal antibodies (mAb). To provide the sensitivity required, complexes of alkaline phosphatase and mouse monoclonal anti-alkaline phosphatase (APAAP) have been used. The speed and reproducibility of the assay was improved with the aid of immunofiltration methodology. Quantitative measurement of HLA-DR antigen expression by ELISA did not correlate directly with the number of mononuclear cells scored positive following immunohistochemical staining of cytocentrifuged preparations. In patients with rheumatoid arthritis, more HLA-DR was expressed on synovial fluid mononuclear cells than on the corresponding cells obtained from peripheral blood.