Li Chang, Geng Honglian, Yang Zaixing, Zhong Renqian
Department of Laboratory Medicine, Shanghai Changzheng Hospital, Second Military Medical University & Clinical Immunology Center of PLA, China.
Clin Lab. 2011;57(1-2):53-7.
Some polymeric forms of immunoglobulin free light chains (FLCs) have been identified, such as dimer, trimer and tetramer, and the quantitative nephelometric assay of kappa and lambda light chains is very important to the diagnosis and management of multiple myeloma (MM), primary systemic amyloidosis (AL), etc. But, whether polymeric molecules could affect the results of the nephelometric assay, is rarely reported.
12 urinary samples from patients with light-chain MM were separated by sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and every sample was run with reduced and nonreduced sample buffer in one gel. Urinary kappa and lambda light chains were measured on the BNII nephelometer. We then added 3 microL beta-mercaptoethanol (2-ME) to the samples to transform the dimers into monomeric forms and measured them again.
10 samples showed obvious dimers by SDS-PAGE, of which 2 samples were kappa light chain dimers. Six samples had decreased quantitative results contrasted with the former values. The two samples of kappa light chain dimers decreased more obviously.
The light chain dimer combined with more antibodies than the monomer and a larger antigen-antibody complex was formed. The larger complex could magnify the reaction between antigen and antibody of the nephelometric assay and therefore false elevated results could measured.
已鉴定出一些免疫球蛋白游离轻链（FLC）的聚合物形式，如二聚体、三聚体和四聚体，κ和λ轻链的定量散射比浊法对多发性骨髓瘤（MM）、原发性系统性淀粉样变性（AL）等疾病的诊断和管理非常重要。但是，聚合物分子是否会影响散射比浊法的结果，鲜有报道。
采用十二烷基硫酸钠-聚丙烯酰胺凝胶电泳（SDS-PAGE）对12例轻链型MM患者的尿液样本进行分离，每个样本在一块凝胶中分别用还原型和非还原型样本缓冲液进行电泳。在BNII散射比浊仪上检测尿液中的κ和λ轻链。然后向样本中加入3μLβ-巯基乙醇（2-ME），将二聚体转化为单体形式，再次进行检测。
10个样本经SDS-PAGE显示出明显的二聚体，其中2个样本为κ轻链二聚体。6个样本的定量结果与之前的值相比有所下降。2个κ轻链二聚体样本下降更为明显。
轻链二聚体比单体结合更多的抗体，形成更大的抗原-抗体复合物。更大的复合物会放大散射比浊法中抗原与抗体之间的反应，从而可能导致检测结果假性升高。
