Aarden L A, Lakmaker F, Feltkamp T E
J Immunol Methods. 1976;10(1):27-37. doi: 10.1016/0022-1759(76)90004-1.
The sensitivity and the specificity of the Farr assay for the detection of antibodies to double stranded (ds) DNA depends very much on the reaction conditions. The interaction between ds DNA and anti-ds DNA is inhibited when ionic strength and pH are increased. ds DNA is bound by normal sera at ionic strength lower than 0.11 M NaCl and at physiological ionic strength when the pH is lower than 7.2. Substantial binding of DNA by normal serum takes place in barbitone, borate or Tris-HCl buffers at concentrations of 30 mM or higher, even at a pH higher than 7.2. Such binding is due to Clq and is only partially prevented by heating the serum for 30 min at 56 degrees C, but 10 mM phosphate in the incubation mixture completely prevents it. Standardization of ionic strength, pH, phosphate concentration, incubation volume and DNA-serum ratio enhances the diagnostic usefulness of the Farr assay.
法尔氏试验检测双链（ds）DNA抗体的敏感性和特异性在很大程度上取决于反应条件。当离子强度和pH值升高时，ds DNA与抗ds DNA之间的相互作用会受到抑制。在离子强度低于0.11 M NaCl且pH值低于7.2时，ds DNA会与正常血清结合；在生理离子强度下，当pH值低于7.2时，ds DNA也会与正常血清结合。在巴比妥、硼酸盐或Tris-HCl缓冲液中，浓度为30 mM或更高时，即使pH值高于7.2，正常血清也会与DNA大量结合。这种结合是由于Clq引起的，通过在56℃下将血清加热30分钟只能部分阻止这种结合，但孵育混合物中10 mM的磷酸盐可完全阻止这种结合。离子强度、pH值、磷酸盐浓度、孵育体积和DNA-血清比例的标准化提高了法尔氏试验的诊断效用。
