Enzyme-linked immunosorbent assay for anti-DNA antibodies using fluorogenic and colorigenic substrates

An enzyme-linked immunosorbent assay is described for the assay of anti-DNA antibodies. The method employs plastic surface for immobilization of the antigen and alkaline phosphatase-linked rabbit anti-human IgG for the detection of immune complex using PNP-P and 4MU-P as substrates. The sensitivity of the assay increased by as much as 16-fold when fluorogenic substrate was used instead of conventional PNP-P and could therefore be employed for the detection of low avidity antibodies. Using PNP-P as substrate 57% of SLE patients were positive for DNA antibody, but if 4MU-P was introduced as substrate, 71% gave a positive response. Moreover, using a fluorogenic substrate, it was possible to minimise the amount of antigen (2 nM bp). The technique is simple, reproducible and of high sensitivity.