Objectives

Up to 3% of patients with monoclonal gammopathies have multiple serum paraproteins. This article investigates whether multiple isotype-matched paraproteins, as seen on capillary zone electrophoresis (CZE), are truly biclonal.

Methods

Sera containing multiple isotype-matched paraproteins were treated with the reducing agent dithiothreitol (DTT) and CZE performed pre- and post-treatment. Band resolution and effect of resolution on quantitation of paraprotein burden was assessed. The Hevylite® turbidimetric assay was also evaluated for ability to quantify such paraproteins.

Results

Among patients with biclonal isotype-matched (BIM) paraproteins, 23/24 (96%) IgA paraproteins resolved into a single band following treatment with DTT compared with only 1/12 (8%) IgG paraproteins. Daratumumab therapy accounted for the second band in 5/9 non-resolving IgGκ paraproteins.

Where initially quantified as a single IgA “complex” (multiple bands in close proximity), the single post-DTT band averaged 2.8 g/L less (P=<0.001), likely due to inclusion of lower amounts of underlying serum proteins (y=0.97x-2.03, R2=0.993).

Quantitating IgA BIM (n=58) using the Hevylite® assay gave higher results (P=0.002) than CZE (y=1.48x–7.13, R2=0.959). In contrast, single IgA paraprotein results (n=48) did not differ between the two methods (P=0.466; y=1.24x – 2.74, R2=0.898), suggesting that polymerisation enhances Hevylite® quantitation.

Conclusions

These results suggest that disulphide-mediated polymerisation of IgA paraproteins is more common than true biclonal gammopathy and support DTT treatment of samples with isotype-matched IgA bands before quantifying by CZE. The Hevylite® assay should be utilised with caution where polymerisation is likely. Where IgGκ BIM paraproteins appear on CZE, Daratumumab therapy should be considered.

目标

高达 3% 的单克隆丙种球蛋白病患者有多种血清副蛋白。本文研究了在毛细管区带电泳 (CZE) 上看到的多个同种型匹配的副蛋白是否真正是双克隆的。

方法

含有多种同种型匹配的副蛋白的血清用还原剂二硫苏糖醇 (DTT) 处理，CZE 进行预处理和后处理。评估了条带分辨率和分辨率对副蛋白负荷定量的影响。还评估了 Hevylite® 浊度测定法量化此类副蛋白的能力。

结果

在具有双克隆同种型匹配 (BIM) 副蛋白的患者中，23/24 (96%) IgA 副蛋白在 DTT 治疗后分解为单一条带，而只有 1/12 (8%) IgG 副蛋白。Daratumumab 治疗占 5/9 非解析 IgGκ 副蛋白中的第二条带。

在最初量化为单个 IgA“复合体”（多个靠近的条带）的情况下，DTT 后单个条带平均减少 2.8 g/L (P=<0.001)，可能是由于包含较少量的基础血清蛋白（ y=0.97x-2.03，R2=0.993）。

使用 Hevylite® 测定法对 IgA BIM (n=58) 进行定量得出的结果 (P=0.002) 高于 CZE (y=1.48x–7.13, R2=0.959)。相反，单个 IgA 副蛋白结果 (n=48) 在两种方法之间没有差异（P=0.466；y=1.24x – 2.74，R2=0.898），表明聚合增强了 Hevylite® 定量。

结论

这些结果表明，二硫化物介导的 IgA 副蛋白聚合比真正的双克隆丙种球蛋白病更常见，并支持在 CZE 量化之前对具有同种型匹配的 IgA 条带的样品进行 DTT 处理。在可能发生聚合反应的情况下应谨慎使用 Hevylite® 检测。如果 IgGκ BIM 副蛋白出现在 CZE 上，则应考虑 Daratumumab 治疗。