Expression of antibody activity measured by ELISA. Anti-ssDNA antibody activity characterized by the shape of the dose-response curve.

To demonstrate the presence or absence of antibodies, results derived from a single serum dilution in an ELISA are sufficient. However, qualitative differences in antibodies are reflected by the shape of dose-response curves. A method based on approximating the absorbance value by a polynomial p(x) = a1x + a2x2, where 1/x is the dilution factor, was used to characterize the dose-response curves in an ELISA for anti=ssDNA antibodies. The parameters used are E = a1 and A = -a2(1)/a2. It can be argues that E gives an estimate of the effective amount of antibodies in the serum and that A is essentially a function of the reaction constants between antibody and antigen.