Reappraisal of PLA2R1 in membranous nephropathy: immunostaining method influence and association with IgG4-dominant phenotype

Abstract

The M-type phospholipase A2 receptor (PLA2R1) was identified recently as a specific target antigen in idiopathic membranous nephropathy. However, the influence of different sample preparation techniques on the immunostaining of PLA2R1 is unclear. Previous studies have identified IgG4 as the dominant subclass of PLA2R1 antibodies. However, it remains unclear whether the IgG subclass profiles of the glomerular immune complexes of PLA2R1-positive and -negative idiopathic membranous nephropathy cases are similar. To address these questions, we conducted the present study of 58 idiopathic membranous nephropathy cases. The PLA2R1 positivity rate for the paraffin-embedded sections was 61%, whereas that for the frozen sections was 65%. Nonspecific background staining was observed in the frozen sections. Discrepancies between different sample preparations occurred in three cases (6%); two cases were PLA2R1-positive in paraffin sections and PLA2R1-negative in frozen sections and one case was PLA2R1-negative in paraffin sections and PLA2R1-positive in frozen sections. Regarding the IgG subclass profile, 89% of the PLA2R1-positive cases demonstrated the IgG4-dominant/codominant phenotype versus 31% of the PLA2R1-negative cases (p < 0.001). Clinical characteristics and pathological findings did not significantly differ between PLA2R1-positive and -negative cases. In summary, the PLA2R1 immunofluorescence results were not affected by the different sample preparation techniques, although paraffin-embedded sections were preferred for the histological detection of PLA2R1 because of the nonspecific background staining observed in frozen sections. The observed lower frequency of the non-IgG4-dominant/codominant phenotype in PLA2R1-negative idiopathic membranous nephropathy cases may suggest that there are heterogeneous subgroups of this disease.

Clinicopathological characteristics of thrombospondin type 1 domain-containing 7A-associated membranous nephropathy

“…The M-type phospholipase A2 receptor (PLA2R) was the first identified major target protein. It is associated with 70–80% of iMN cases in Western countries [ 2 – 4 ], and with 50–60% of cases in Japan [ 5 – 7 ]. There is considerable evidence to indicate that anti-PLA2R antibody levels can serve as a biomarker for assessing MN disease activity and treatment efficacy, as high anti-PLA2R antibody titre is associated with weaker response to immunosuppressive drugs, longer time to remission [ 8 ] and increased risk of kidney failure [ 9 , 10 ].…”

Membranous glomerulonephritis – a common, unspecific pattern of glomerular injury

“…The data collected so far on the complement system involvement in MN evolution is still not coherent. C3 and C5b-9 are universally present in subepithelial deposits, and, as was already mentioned, IgG4 seems to be the dominant/codominant subclass in PLA2R-associated MN [23,79]. In contrast to other IgG subclasses, IgG4 does not activate the classical complement system, which points to the alternative or lectin pathways as the major operators of C5-9 complex formation in pMN.…”

“…In pMN the dominating IgG subclass in the subepithelial IC is IgG4 [23]. Studies addressing the IgG subclass distribution across different stages of pMN show that in the early stage there is a domination of IgG1, whereas IgG4 is the most prevalent one in the later phase of this glomerulopathy evolution.…”

“…The findings of Beck et al opened a new path of research for new diagnostic and prognostic tools in MN. Over the last decade many studies focusing on aPLA2R-ABs and their antigen target were performed across the world [19,20,21,22,23].…”

“…Some patients who produce low quantities of the antibody may be seronegative until the antibody has saturated the PLA2R binding sites on podocytes and only then become seropositive [24]. Since the absence of aPLA2R-ABs in an MN patient's serum does not exclude the diagnosis of PLAR-related MN [22], the additional method allowing for its recognition is the identification of PLA2R antigen in glomerular deposits [22,23,25]. PLA2R tissue staining was found to be particularly useful in the case of delayed serum sampling [22]; it also created the possibility of a retrospective diagnosis of PLA2R-related MN [22], especially because tissue preparation (frozen vs. paraffin embedded) did not significantly affect staining results [23].…”