Environmental pathogens are suspected to aggravate renal injury in IgA nephropathy (IgAN), but neither underlying mechanisms nor specific exogenous antigens have been identified. In this study, a genome-wide scan of ddY mice, which spontaneously develop IgAN, was performed, and myeloid differentiation factor 88 (MyD88) was identified as a candidate gene for progression of renal injury ( 2 ϭ 21.103, P ϭ 0.00017). For evaluation of the potential influence of environmental pathogens on progression of renal injury, ddY mice were housed in either conventional or specific pathogen-free conditions. Expression of genes encoding toll-like receptors (TLR) and the signaling molecule MyD88 were quantified by real-time reverse transcription-PCR in splenocytes. Although the housing conditions did not affect the prevalence of IgAN, the severity of renal injuries was higher in the conventionally housed group. Mice that had IgAN and were housed in conventional conditions had higher levels of TLR9 and MyD88 transcripts than mice that had IgAN and were housed in specific pathogen-free conditions. Furthermore, nasal challenge with CpG-oligodeoxynucleotides, which are ligands for TLR9, aggravated renal injury, led to strong Th1 polarization, and increased serum and mesangial IgA. For investigation of whether these results may be generalizable to humans, single-nucleotide polymorphisms in the TLR9 and MyD88 genes were analyzed in two cohorts of patients with IgAN; an association was observed between TLR9 polymorphisms and disease progression. In summary, these findings suggest that activation of the TLR9/MyD88 pathway by common antigens may affect the severity of IgAN.

IgA nephropathy is the most common form of progressive glomerulonephritis although the pathophysiology of this nephropathy is unclear. The ddY mouse is a spontaneous animal model with variable incidence and extent of glomerular injury mimicking human IgA nephropathy. Here, we transplanted bone marrow cells from 20-week-old ddY mice with beginning or quiescent IgA nephropathy into irradiated similar ddY mice, C57Bl/6 (Th1 prone) mice, or BALB/c (Th2 prone) mice. Serum IgA/IgG complex and Th1/Th2 polarization of spleen cells was determined by enzyme-linked immunosorbent assay and confirmed by fluorescent cytometric analysis. The ddY mice with commencing IgA nephropathy demonstrated strong polarization toward Th1, while those with quiescent disease were Th2 polarized. Serum levels of IgA/IgG2a immune complex significantly correlated with the severity of the glomerular lesions. Bone marrow taken from mice with commencing IgA nephropathy conferred IgA nephropathy with Th1 polarization in recipient-quiescent mice, while transplantation from the quiescent mice ablated glomerular injury and mesangial IgA/IgG deposition in those commencing IgA disease. However, adoptive transfer of CD4(+) T cells from those whose disease began failed to induce any IgA deposition or renal injury. Our study suggests that bone marrow cells, presuming IgA producing cells, may initiate this disease. Th1 cells may be involved in the pathophysiology of the disease after glomerular IgA deposition.

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Structural aberrations of O-linked glycans present in the IgA1 hinge region are associated with IgA nephropathy, but their contribution to its pathogenesis remains incompletely understood. In this study, mice implanted with hybridoma secreting 6-19 IgA anti-IgG2a rheumatoid factor, but not 46-42 IgA rheumatoid factor bearing the same IgA allotype, developed mesangial deposits consisting of IgA, IgG2a, and C3. Studies in immunoglobulin-and C3-deficient mice revealed that the development of these glomerular lesions required the formation of IgA-IgG2a immune complexes and subsequent activation of complement. The proportion of polymeric and monomeric forms, the IgG2a-binding affinity, and the serum levels of IgA-IgG2a immune complexes were similar between 6-19 IgA-and 46-42 IgA-injected mice. In contrast, the analysis of oligosaccharide structures revealed highly galactosylated O-linked glycans in the hinge region of 6-19 IgA and poorly O-glycosylated in the hinge region of 46-42 IgA. Furthermore, the structure of N-linked glycans in the CH1 domain was the complex type in 6-19 IgA and the hybrid type in 46-42 IgA. In summary, this study demonstrates the presence of O-linked glycans in the hinge region of mouse IgA and suggests that 6-19 IgA rheumatoid factor-induced GN could serve as an experimental model for IgA nephropathy.

Background Recent clinical reports indicate a correlation between gross hematuria after the coronavirus 2019 (COVID-19) vaccination in patients with glomerulonephritis, especially immunoglobulin A nephropathy (IgAN). Furthermore, healthcare workers in Japan were initially vaccinated with an mRNA vaccine from February 17, 2021, and some of them experienced gross hematuria after receiving the vaccination. Methods We conducted a web-based survey of the councilor members of the Japanese Society of Nephrology (581 members, 382 facilities) to elucidate the relationship between gross hematuria and COVID-19 vaccination. Results In the first survey, 27 cases (female: 22, 81.5%) of gross hematuria were reported after receiving a COVID-19 vaccination. Of them, 19 (70.4%) patients were already diagnosed with IgAN at the occurrence of gross hematuria. Proteinuria appeared in eight of the 14 (57.1%) cases with no proteinuria before vaccination and hematuria in five of the seven (71.4%) cases with no hematuria before vaccination. The second survey revealed that a renal biopsy was performed after vaccination in four cases, all of whom were diagnosed with IgAN. Only one case showed a slightly increased serum creatinine level, and no patients progressed to severe renal dysfunction. Conclusion This study clarified the clinical features of gross hematuria after a COVID-19 vaccination. Because there was no obvious progression to severe renal dysfunction, safety of the COVID-19 vaccination is warranted at least in the protocol of inoculation twice.

The envelope glycoprotein gp70 of endogenous retroviruses implicated in murine lupus nephritis is secreted by hepatocytes and its expression is controlled by Sgp3 (serum gp70 production 3) and Sgp4 loci derived from lupusprone mice. Among three different endogenous retroviruses (ecotropic, xenotropic and polytropic), xenotropic viruses are considered to be the major source of serum gp70. Although the abundance of xenotropic viral gp70 RNA in livers was up-regulated by the presence of these two Sgp loci, it has not yet been clear whether Sgp3 and Sgp4 regulate the expression of a fraction or multiple xenotropic viruses present in mouse genome. To address this question, we determined the genetic origin of xenotropic viral sequences expressed in wildtype and two different Sgp congenic C57BL/6 mice. Among 14 xenotropic proviruses present in the C57BL/6 genome, only two proviruses (Xmv10 and Xmv14) were actively transcribed in wild-type C57BL/6 mice. In contrast, Sgp3 enhanced the transcription of Xmv10 and induced the transcription of three additional xenotropic viruses (Xmv15, Xmv17 and Xmv18), while Sgp4 induced the expression of a different xenotropic virus (Xmv13). Notably, stimulation of TLR7 in Sgp3 congenic C57BL/6 mice led to a highly enhanced expression of potentially replication-competent Xmv18. These results indicated that Sgp3 and Sgp4 independently regulated the transcription of distinct and restricted sets of xenotropic viruses in trans, thereby promoting the production of nephritogenic gp70 autoantigens. Furthermore, the induced expression of potentially replication-competent xenotropic viruses by Sgp3 may contribute to the development of autoimmune responses against gp70 through the activation of TLR7.

Monoclonal 6-19 IgG3 anti-IgG2a rheumatoid factor derived from lupus-prone MRL-Fas lpr mice can induce GN and cryoglobulinemia, but the features that confer nephritogenic potential are not completely understood. Asparagine-linked oligosaccharide chains of 6-19 IgG3 mAb are poorly galactosylated and hardly sialylated, possibly contributing to the pathogenic potential of 6-19 IgG3 rheumatoid factors. Here, we used the 6-19 model of cryoglobulin-associated GN to define the relative contributions of galactosylation and sialylation, in relation to cryoglobulin activity, to the nephritogenic potential of IgG3 antibodies. We generated one highly sialylated and two distinct more galactosylated 6-19 IgG3 rheumatoid factor variants. Although the mere extent of galactosylation had no effect on either the cryogenic and nephritogenic activities of 6-19 IgG3 rheumatoid factor, terminal sialylation attenuated the nephritogenic potential of 6-19 IgG3 by limiting its cryoglobulin activity. These data suggest a protective role of IgG sialylation against the development of cryoglobulin-mediated GN, highlighting the anti-inflammatory activity of sialylated IgG antibodies. Cryoglobulins are a heterogeneous group of Igs that precipitate at temperatures ,37°C, with resolution upon warming. 1,2 Most cryoglobulins are either monoclonal Ig or Ig complexes in which one component, usually IgM, has rheumatoid factor (RF) activity. 1,2 Monoclonal cryoglobulins are mainly associated with various lymphoproliferative disorders, whereas mixed cryoglobulins are often found in sera of patients with autoimmune diseases, such as SLE and rheumatoid arthritis, or with chronic infectious diseases. The presence of cryoglobulins can result in a wide range of vascular, renal, and neurologic complications, likely depending on their concentration, their temperature-dependent solubility behavior, and the nature and type of proteins involved. 2 Antibodies of the IgG3 subclass in humans and mice have the unique physicochemical property that allows them to self-associate via Fc-Fc interactions and to display cryoglobulin activity, independently of their specificities. [3][4][5][6][7][8] Nucleotide sequence analysis of the variable regions of cryogenic and noncryogenic IgG3 mAbs, in combination with the assessment of mutant antibodies, showed that cryoglobulin activity of IgG3 was associated with the presence of more positively charged amino-acid residues at positions 6 and 23 of the heavy-chain variable domain. 9,10 Moreover, structural analysis of asparagine-linked biantennary complex-type oligosaccharide chains (N-glycans) attached to the CH2 domain of different IgG3 mAbs revealed an inverse correlation

Background Severe acute respiratory syndrome Coronavirus 2 has rapidly spread worldwide, with acute kidney injury (AKI) as one of the manifestations with unknown causal mechanisms. We aimed to investigate tubular injury by assessing tubular markers and their association with the severity of Coronavirus disease 2019 . Methods We examined the associations between laboratory markers and urinary levels of N-acetyl-β-d-glucosaminidase (uNAG), β2-microglobulin (u β2MG), α1-microglobulin (u α1MG), and liver-type fatty acid binding protein (L-FABP). We studied 18 COVID-19 patients without previous chronic kidney disease and analyzed the relationship between the urinary biomarkers and inflammatory markers in patients with severe (n = 7) or non-severe (n = 11) COVID-19, defined by requirements of supplemental oxygen. Results Fourteen patients (78%) showed abnormal urinalysis findings and two (11%) developed AKI. Patients with severe COVID-19 had significantly higher levels of proteinuria, uNAG, uβ2MG, uα 1MG, and L-FABP than those with non-severe disease. Serum levels of interleukin-6 (IL-6) were significantly higher on admission in all severe COVID-19 cases and correlated with the levels of L-FABP, uβ2MG, uα1MG, uNAG, and proteinuria. Moreover, the changes in serum IL-6 (ΔIL-6) levels from baseline to 7 days after admission significantly correlated with ΔL-FABP and Δuβ2MG. Conclusions Levels of tubular injury markers, especially L-FABP and uβ2MG, were significantly associated with IL-6 levels even in patients with no evident AKI. This suggests that L-FABP and uβ2MG could be useful as early detective biomarkers for COVID-19 associated renal injury.