Valentine Helen, Dawnay Anne
Clinical Biochemistry, Mid and South Essex NHS Foundation Trust, Essex, UK.
Clinical Biochemistry, Barts Health NHS Trust, London, UK.
Ann Clin Biochem. 2021 Nov;58(6):586-592. doi: 10.1177/00045632211029327. Epub 2021 Jul 4.
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, are truly biclonal.
Serum samples containing multiple isotype-matched paraproteins were treated with the reducing agent dithiothreitol, and capillary zone electrophoresis was performed pre- and post-treatment. Band resolution and effect of resolution on quantitation of paraprotein burden were assessed. The Hevylite turbidimetric assay was also evaluated for ability to quantify such paraproteins.
Among patients with biclonal isotype-matched paraproteins, 23/24 (96%) IgA paraproteins resolved into a single band following treatment with dithiothreitol 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 postdithiothreitol band averaged 2.8 g/L less (<0.001), likely due to inclusion of lower amounts of underlying serum proteins (y = 0.97x-2.03, R=0.993). Quantitating IgA biclonal isotype matched ( = 58) using the Hevylite assay gave higher results ( = 0.002) than capillary zone electrophoresis (y = 1.48x-7.13, R=0.959). In contrast, single IgA paraprotein results ( = 48) did not differ between the two methods ( = 0.466; y = 1.24x-2.74, R=0.898), suggesting that polymerisation enhances Hevylite quantitation.
These results suggest that disulphide-mediated polymerisation of IgA paraproteins is more common than true biclonal gammopathy and support dithiothreitol treatment of samples with isotype-matched IgA bands before quantifying by capillary zone electrophoresis. The Hevylite assay should be utilized with caution where polymerisation is likely. Where IgGκ biclonal isotype-matched paraproteins appear on capillary zone electrophoresis, daratumumab therapy should be considered.
高达3%的单克隆丙种球蛋白病患者存在多种血清副蛋白。本文研究了在毛细管区带电泳中观察到的多种同型匹配副蛋白是否真的是双克隆性的。
对含有多种同型匹配副蛋白的血清样本用还原剂二硫苏糖醇进行处理，并在处理前后进行毛细管区带电泳。评估条带分辨率以及分辨率对副蛋白负荷定量的影响。还评估了Hevylite比浊法对这类副蛋白的定量能力。
在双克隆同型匹配副蛋白患者中，23/24（96%）的IgA副蛋白在用二硫苏糖醇处理后分解为单一条带，而IgG副蛋白只有1/12（8%）分解为单一条带。达雷妥尤单抗治疗导致5/9未分解的IgGκ副蛋白出现第二条带。最初被定量为单一IgA“复合物”（多条紧密相邻的条带）的情况，二硫苏糖醇处理后的单一条带平均少2.8 g/L（<0.001），可能是由于包含的基础血清蛋白量较少（y = 0.97x - 2.03，R = 0.993）。使用Hevylite检测法对IgA双克隆同型匹配（n = 58）进行定量，其结果（P = 0.002）高于毛细管区带电泳（y = 1.48x - 7.13，R = 0.959）。相比之下，两种方法对单一IgA副蛋白结果（n = 48）没有差异（P = 0.466；y = 1.24x - 2.74，R = 0.898），这表明聚合作用增强了Hevylite检测法的定量。
这些结果表明，IgA副蛋白的二硫键介导的聚合比真正的双克隆丙种球蛋白病更常见，并支持在通过毛细管区带电泳定量之前，用二硫苏糖醇处理具有同型匹配IgA条带的样本。在可能存在聚合的情况下，应谨慎使用Hevylite检测法。当毛细管区带电泳出现IgGκ双克隆同型匹配副蛋白时，应考虑达雷妥尤单抗治疗。
