Bentley-Hibbert S I, Quan X, Newman T, Huygen K, Godfrey H P
Departments of Pathology, New York Medical College, Valhalla, New York 10595, USA.
Infect Immun. 1999 Feb;67(2):581-8. doi: 10.1128/IAI.67.2.581-588.1999.
Antigen 85 (Ag85) complex proteins are major secretory products of Mycobacterium tuberculosis and induce strong cellular and humoral immune responses in infected experimental animals and human beings. We have previously shown that nanogram doses of these 30- to 32-kDa fibronectin-binding proteins inhibit local expression of delayed hypersensitivity by a T-cell fibronectin-dependent mechanism. Circulating levels of Ag85 might be expected to be elevated in patients with active tuberculosis and possibly to play a role in systemic anergy in these patients. To test this hypothesis, Ag85 was measured in serum and urine by a monoclonal antibody-based dot immunobinding assay in 56 patients and controls with known skin test reactivity. Median serum Ag85 levels were 50- to 150-fold higher in patients with active tuberculosis than in patients with active M. avium-intracellulare disease or other nontuberculous pulmonary disease or in healthy controls (P < 0.001). The median and range of serum Ag85 in patients with active tuberculosis was not significantly different between skin test-positive and -negative subjects. Patients with active M. avium disease could be distinguished from those with disease due to M. tuberculosis by monoclonal anti-Ag85 antibodies of appropriate specificities. No increases in urinary Ag85 were detected in any patient, regardless of the Ag85 level in serum. Chromatographic analysis and immunoprecipitation studies of serum revealed that Ag85 existed in the serum of these patients complexed to either fibronectin or immunoglobulin G (IgG). Uncomplexed circulating Ag85 was demonstrable in serum from fewer than 20% of patients with active tuberculosis. In patients with active tuberculosis, Ag85 is therefore likely to circulate primarily as complexes with plasma fibronectin and IgG rather than in unbound form. The existence of Ag85 complexes with plasma proteins would account for its lack of urinary clearance.
抗原85（Ag85）复合蛋白是结核分枝杆菌的主要分泌产物，在受感染的实验动物和人类中可诱导强烈的细胞免疫和体液免疫反应。我们之前已经表明，纳克剂量的这些30至32 kDa的纤连蛋白结合蛋白通过T细胞纤连蛋白依赖性机制抑制迟发型超敏反应的局部表达。活动性结核病患者的循环Ag85水平可能会升高，并可能在这些患者的全身无反应性中起作用。为了验证这一假设，我们采用基于单克隆抗体的斑点免疫结合试验，对56例已知皮肤试验反应性的患者及对照者的血清和尿液中的Ag85进行了检测。活动性结核病患者的血清Ag85水平中位数比鸟分枝杆菌胞内菌病患者、其他非结核性肺部疾病患者或健康对照者高50至150倍（P < 0.001）。活动性结核病患者中，皮肤试验阳性和阴性受试者的血清Ag85中位数及范围无显著差异。通过具有适当特异性的抗Ag85单克隆抗体，可将活动性鸟分枝杆菌病患者与结核分枝杆菌病患者区分开来。无论血清中Ag85水平如何，未在任何患者中检测到尿液Ag85增加。血清的色谱分析和免疫沉淀研究表明，Ag85在这些患者的血清中与纤连蛋白或免疫球蛋白G（IgG）形成复合物存在。活动性结核病患者中，不到20%的患者血清中可检测到未结合的循环Ag85。因此，在活动性结核病患者中，Ag85可能主要以与血浆纤连蛋白和IgG的复合物形式循环，而非以未结合形式存在。Ag85与血浆蛋白形成复合物的存在可解释其缺乏经尿液清除的现象。
