Immunoglobulin Repertoire Analysis in PGNMID

Proliferative glomerulonephritis with monoclonal immunoglobulin deposits (PGNMID) is currently classified within the spectrum of monoclonal gammopathy of renal significance (MGRS). However, PGNMID features an unexpected low rate of detectable monoclonal gammopathy, questioning the reality of an underlying clonal disorder in most cases. We reviewed a cohort of 56 PGNMID patients with focus on hematological characteristics. To detect discreet underlying clones, we used a highly sensitive high-throughput Ig repertoire sequencing assay from RNA bone marrow (RACE-RepSeq). We also challenged the monoclonality of kidney deposits using immunofluorescence with antibodies specific for light chain (LC) variable region subgroups. RACE-RepSeq detected a bone marrow clone corresponding to the deposited Ig in only 23% of the whole cohort. As previously reported, PGNMID-IgG3 was the predominant subtype (41/56, 73%), with an overrepresentation of IgG3kappa deposits (33/56, 59%). The low prevalence of clonal disorders was driven by PGNMID-IgG3 cases, with only 4/41 patients showing an IgG3-secreting bone marrow clone by RACE-RepSeq. In all seven clone-negative PGNMID-IgG3kappa cases studied by immunofluorescence with anti-LC variable domain antibodies, glomerular deposits stained for all tested V? subgroups, ruling out their monoclonal nature. Compared to control subjects, immunoglobulin repertoire analyses in 24 patients without a detectable clone failed to detect any bias toward the deposited isotype, but showed increased IgG1 representation, suggesting an infectious trigger. In conclusion, PGNMID is a heterogeneous condition. The predominant subtype most often involves oligo or polyclonal production of nephrotoxic IgG3 and does not derive from a B-cell disorder. Such cases should no longer be classified as MGRS.

伴单克隆免疫球蛋白沉积的增生性肾小球肾炎（Proliferative glomerulonephritis with monoclonal immunoglobulin deposits, PGNMID）目前被归类于肾意义单克隆丙种球蛋白病（monoclonal gammopathy of renal significance, MGRS）的范畴。然而，PGNMID患者可检测到单克隆丙种球蛋白的比例意外偏低，这使得多数病例中存在潜在克隆性疾病这一假设受到质疑。本研究回顾性分析了56例PGNMID患者队列，重点关注其血液学特征。为检出隐匿的潜在克隆，我们采用了基于骨髓RNA的高灵敏度高通量免疫球蛋白组库（immunoglobulin repertoire）测序检测技术（RACE-RepSeq）。同时，我们使用针对轻链（light chain, LC）可变区亚组的特异性抗体进行免疫荧光染色，以验证肾脏沉积产物的单克隆性。在全部队列中，RACE-RepSeq仅在23%的患者中检测到与肾脏沉积免疫球蛋白对应的骨髓克隆。如既往研究报道，PGNMID以IgG3亚型为主（41/56，73%），其中IgG3κ沉积尤为多见（33/56，59%）。克隆性疾病的低检出率主要由PGNMID-IgG3亚型病例导致：在41例该亚型患者中，仅4例通过RACE-RepSeq检测到分泌IgG3的骨髓克隆。在7例通过抗轻链可变域抗体免疫荧光检测的克隆阴性PGNMID-IgG3κ病例中，肾小球沉积产物可与所有受试的Vκ亚组抗体结合，从而排除了其单克隆属性。与对照组相比，24例未检出克隆的患者的免疫球蛋白组库分析未显示出与沉积免疫球蛋白亚型相关的偏好性，但IgG1占比升高，这提示感染可能为触发因素。综上，PGNMID是一种异质性疾病。其主要亚型通常由肾毒性IgG3的寡克隆或多克隆产生所介导，并非起源于B细胞疾病。此类病例不应再被归类为MGRS。