A Rapid and Sensitive Cellular Enzyme-Linked Immunoabsorbent Assay (CELISA) for the Detection and Quantitation of Antibodies against Cell Surface Determinants II. Optimal Reagent Concentrations and Predictive Analysis

A cellular enzyme-linked immunosorbent assay (CELISA) was developed for the detection and quantification of antibodies elicited against allogeneic cell surface determinants. The technique uses a solid-phase cell matrix created by fixing cells with a mild formalin solution onto the bottom of a 96-well microtiter plate. A primary layer of alloantisera is first reacted against rat target cells. The secondary antibody, peroxidase conjugated antirat IgG, is then added to each well and serves as the second sandwich layer. Optimal reagent concentrations were determined by serial dilution analysis of various cell concentrations and secondary antibody dilutions. It was found that 200,000 cells per well was the optimal target cell concentration. However, 100,000 cells per well was also sufficient to run the assay with acceptable performance characteristics. Even lower cell concentrations of 10,000 and 20,000 cells/well, although not optimal, also produced acceptable results. Secondary antibody concentration with respect to the optimal cell concentration was determined to be 1:500. At 200,000 cells per well and a 1:500 secondary antibody dilution, the assay presented excellent coefficients of determination and high positive to negative ratios. The reaction was found to be very sensitive in yielding high antibody titers with low background levels and could be defined mathematically as a linear-log function. Titers of multiple unknown alloantibody samples were easily and accurately predicted in an automated manner by regression analysis form known standards. This immunoassay will be useful in studies of cell surface determinant expression and quantitation of antibodies reactive to such markers.