Gharavi A E, Elkon K B, Schifferli J A, Hughes G R
J Clin Lab Immunol. 1981 Nov;6(3):251-5.
Anti-DNA antibodies were assessed in 33 patients with active systemic lupus erythematosus (SLE) by the immunofluorescence Crithidia luciliae (CL) and the Farr assays. Eleven patients demonstrated complement (C3) fixation in the CL assay. Although 6 out of 9 patients with active nephritis showed complement fixation, 6 patients without overt renal disease were also positive in this assay. The ability to fix C3 was strongly associated with the total amount of anti-DNA antibodies as determined by both the CL and Farr assays (P less than 0.001). IgM anti-DNA antibodies were detected only in sera with complement fixing anti-DNA antibodies. Isolated whole IgG, but not the F(ab')2 fragment containing anti-DNA activity, fixed C3 on the Crithidia substrate. In depletion and reconstitution studies with human complement components, it was established that anti-DNA antibodies fixed C3 through the classical complement pathway although factors B and D of the alternative pathway were effective in C3 amplification. Properdin was also detected on the antigen-antibody complex but did not appear to be essential for maximal C3 fixation. Anti-DNA antibodies therefore fix complement by their Fc portion, form a classical pathway convertase, and recruit factors B and D of the C3b amplification loop when they bind to a fixed antigen.
采用免疫荧光法检测克氏锥虫（CL）和法尔氏试验，对33例活动性系统性红斑狼疮（SLE）患者的抗DNA抗体进行了评估。11例患者在CL试验中表现出补体（C3）固定。虽然9例活动性肾炎患者中有6例显示补体固定，但6例无明显肾脏疾病的患者在该试验中也呈阳性。CL试验和法尔氏试验测定结果显示，C3固定能力与抗DNA抗体总量密切相关（P小于0.001）。仅在具有补体固定抗DNA抗体的血清中检测到IgM抗DNA抗体。分离的完整IgG可在克氏锥虫底物上固定C3，但含有抗DNA活性的F(ab')2片段则不能。在用人补体成分进行的消耗和重建研究中，证实抗DNA抗体通过经典补体途径固定C3，尽管替代途径的B因子和D因子在C3放大中起作用。在抗原-抗体复合物上也检测到备解素，但它似乎不是最大程度C3固定所必需的。因此，抗DNA抗体通过其Fc部分固定补体，形成经典途径转化酶，并在与固定抗原结合时募集C3b放大环的B因子和D因子。
