A sensitive solid phase microradioimmunoassay for anti‐double stranded DNA antibodies

Publisher Website
Google Scholar
Abstract
A sensitive solid phase microradioimmu‐noassay has been developed for measurement of antidouble stranded DNA (dsDNA) antibodies. In this procedure, advantage has been taken of the capacity of poly‐L‐lysine (PLL) to facilitate the binding of pure dsDNA to plastic surfaces. In the absence of PLL, binding did not occur. Diluted sera were incubated in PLL‐treated dsDNA‐coated microtitration trays and anti‐dsDNA Ig was measured using affinity purified125I‐anti‐Ig of high specific activity. The synthetic DNA, poly dA‐dT, was used as a model for dsDNA. In initial experiments, specific anti‐DNA binding could not be demonstrated because of high background binding of patient Ig to PLL‐treated surfaces. This was reduced by diluting test sera and anti‐Ig in buffer containing 2% BGG and 1% BSA. Specificity of the assay for DNA was demonstrated by absorbing the anti‐DNA activity on DNA‐coated plastic. The binding of systemic lupus erythema‐tosus (SLE) patient serum Ig to poly dA‐dT coated trays did not diminish after digestion with nuclease S1, suggesting that the synthetic polymer is an appropriate model for dsDNA. Patient and normal sera were screened for anti‐dsDNA activity using poly dA‐dT as antigen. None of the 38 normal sera, 23 of 35 active SLE sera, 1 of 25 treated SLE, 4 of 35 rheumatoid arthritis, 3 of 35 scleroderma, and 1 of 13 polymyositis sera demonstrated positive anti‐dsDNA activity. The anti‐dsDNA values obtained in the radioimmunoassay correlated significantly with those obtained in the Crithidia luciliae assay.