29th Annual Meeting of the Glomerular Disease Collaborative Network

Updates on the Pathogenesis IgA Nephropathy and IgA Vasculitis (HSP)

J. Charles Jennette, M.D.Brinkhous Distinguished Professor and Chair of Pathology and Laboratory Medicine

University of North Carolina at Chapel Hill

IgA NEPHROPATHYIgA nephropathy is glomerular disease with IgA dominant or codominant mesangial immunoglobulin

(Predominantly IgA1)

0

100

200

300

400

500

600

700

1‐9 10‐19 20‐29 30‐39 40‐49 50‐59 60‐69 70‐79 >79

Lupus IgA Nep

ANCA GN TBM Lesion

Fibrillary GN Post Infect GN

Anti‐GBM GN Hereditary Nep

Causes of Nephritis

Lupus GN

IgAN

ANCA GN

Frequency of Renal Biopsy Diagnoses vs Age at UNC from 1985-2007

Jennette JC, Falk RJ. NKF Primer on Kidney Disease, 6th Ed, 2014, Chapter 16:152-163

Anti-GBM GN

IgA Nephropathy

mesangial immune complex deposits

Focal thinning of the GBM

Mesangial dense deposits

RBC penetrating the glomerular capillary wall in thin basement membrane lesion

Collar et al. Kid Intern 59:2069-2072, 2001

HistologicallyNormal

Glomeruli

Focal or DiffuseMesangioprolifertiveGlomerulonephritis

Focal or DiffuseProliferative or Necrotizing

Glomerulonephritis

Focal or DiffuseSclerosing

Glomerulonephritis

CrescenticGlomerulonephritis

Frequency in Biopsy Specimens

IgA Nephropathy

HistologicallyNormal

Glomeruli

Focal or DiffuseMesangioprolifertiveGlomerulonephritis

Focal or DiffuseProliferative or Necrotizing

Glomerulonephritis

Focal or DiffuseSclerosing

Glomerulonephritis

CrescenticGlomerulonephritis

IgA Nephropathy

AsymptomaticHem / Proteinuria

Mild to Moderate Nephritis Severe to

Rapidly progressive Nephritis

Chronic Nephritis

Analysis of the Oxford Data Using the ISN/RPS Classification Approach

J C Jennette, Y Hu, SL Hogan, S Troyanov, M Haas. Unpublished data

IgA NEPHROPATHY

Mesangial IgA Mesangial and Capillary Wall IgA

0

510

1520

25

3035

4045

50

% IgA Nephropathy Specimens with Capillary Wall Electron Dense Deposits Relative to Histologic Phenotype

n=447

Mesangial IgA Mesangial and Capillary Wall IgA

Shubha S. Bellur, et al. Nephrol Dial Transplant (2011) 26: 2533–2536

• The presence of capillary wall IgA deposits was associated with a higher mesangial cellularity score and endocapillary proliferation.

• The presence of IgG was associated with a higher mesangial cellularity score and endocapillary proliferation.

• There was no significant association between the location of IgA or the presence of IgG and rate of loss of renal function.

• There was a trend towards poorer renal survival in those patients with glomerular IgG.

IgA nephropathy probably can be caused by multiple different etiologies and pathogenic processes:

1) abnormally glycosylated IgA

2) antibodies against abnormally glycosylated IgA

3) reduced clearance of circulating IgA complexes

4) increased affinity for or reduced clearance of IgA deposits from the glomerular mesangium

5) excessive IgA antibody production in response to mucosal antigen exposure

6) increased permeability of mucosa to antigen

7) combinations of these factors

Aberrant glycosylation of IgA1 may be caused by genetically determined aberrant mucosal immune responses to infections.

IgA1 but not IgA2 has a hinge region with 0-linked glycan chains. Each O-glycan chain is based on a core N-acetyl galactosamine unit (GalNAc) O-linked to serine or threonine. This can exist alone but usually carries galactose and sialic acid. Each IgA1 molecule can carry a mixture of chain types.

Ser/Thr-O-GalNAc

Ser/Thr-O-GalNAc--Galactose

Ser/Thr-O-GalNAc--Galactose-Sialic Acid

Ser/Thr-O-GalNAc----Galactose-Sialic Acid-

Sialic Acid

VL

CLVH

CH1

CH2

CH3

Hinge Region

IgA1

In IgA nephropathy and IgA vasculitis, serum IgA1 has reduced terminal sialation and galactosylation (X), resulting in increased

exposure of terminal GalNAc.

Patients with IgA nephropathy have increased serum galactose-deficient IgA1 levels. Moldoveanu Z, Wyatt RJ, et al. Kidney Int. 2007;71:1148-54.

A lectin that recognizes N-acetylgalactosamine was used in an ELISA to measure serum galactose-deficient IgA1. The diagnostic sensitivity 76.5%, with specificity 94%; the positive predictive value was 88.6% and the negative predictive value was 78.9%.

Abnormal IgA glycosylation in Henoch-Schonlein purpura restricted to patients with clinical nephritis. Allen AC, Willis FR, Beattie TJ, Feehally J. Nephrol Dial Transplant. 1998 Apr;13(4):930-4.

Children with HSP nephritis showed significantly higher IgA1-VV binding than children with HSP lacking renal involvement (P=0.004), children with post-streptococcal GN (P=0.002), or control children (P=0.005).

Adults with IgAN showed significantly higher IgA1-VV binding than adults with non-IgA glomerulonephritis or adult controls. There was no difference in IgA1-VV binding between adults with HSPN and IgAN.

Aberrant sialylation of serum IgA1 was associated with prognosis of patients with IgA nephropathy

Ding JX, et al. Clin Immunol. 2007;125:268-74.

Glycopeptides in higher mass range contain more sialic acids

Healthy Control

5 5 4

5 4 4

5 4 3

5 4 3

5 3 2 4 4 3

5 44 4

4 3

5 3 34 4 4

5 3GalNAcGalactoseSialic acid

1

1

11

m/z

1-2 sialic acids per glycopeptide

3-4 sialic acids per glycopeptide

IgA1 hinge glycopeptide characterization by quadrupole orthogonal acceleration time-of-flight MS & MS/MS tandem mass spectroscopy (Q-TOF LC-MS/MS)

Provided by Olivier Lardinois, PhD, UNC Kideny Center

Active IgAN

Healthy Control 

Healthy Control treated with neuraminidase(=sialidase) 

Quadrupole orthogonal acceleration time-of-flight tandem mass spectroscopy in MS & MS/MS modes

(Q‐TOF LC‐MS/MS) 

Provided by Olivier Lardinois, PhD, UNC Kideny Center

Relative abun

dance

0.000

0.200

0.400

0.600

0.800

1.000

1.200

5 Healthy Controls (n = 5)Average of: 6 Active IgAN(n = 6)

Comparison of glycosylation profiles between healthy controls and active IgAN

NeuAc = Sialic acid;   Gal = Galactose;   GalNAc = N‐Acetylgalactosamine

Conclusion: Sialylation is lower in IgANProfiles with 2 or more sialic acids are decreased

Provided by Olivier Lardinois, PhD, UNC Kideny Center

IgA1

IgG

Glycan-specific IgG antibodies may form immune complexes with aberrantly glycosylated IgA1

Glycan-specific IgG antibodies have 88% specificity and 95% sensitivity for IgA nephropathy

Suzuki H, et al. Aberrantly glycosylated IgA1 in IgA nephropathy patients is recognized by IgG antibodies with restricted heterogeneity. J Clin Invest. 2009;119:1668-77

Correlation between severityof hematuria/proteinuria and serum Gd-IgA1 or IgA/IgG-IC

Suzuki H, et al. Clin Exp Nephrol. 2014;18:770-7.

Hematuria 1+ to 4+

Hematuria 1+ to 4+

Proteinuria 1+ to 4+

Proteinuria 1+ to 4+

Serum Abnormal

IgA1 Glycosylation

Serum IgA-IgG Immune

Complexes

Abnormally glycosylated IgA1 molecules ( ), even in the absence of antigen, self aggregate or bind to antibodies directed against the abnormal glycosylation ( ) and localize in the glomerular mesangium where they activate complement by the lectin and alternative pathways..

Hypothesis: Glycan-specific IgG antibodies binding to abnormally gylcosylated IgA cause IgA nephropathy

Discovery of new risk loci for IgA nephropathy implicates genes involved in immunity against

intestinal pathogens.

Kiryluk K, et al. Nat Genet. 2014;46:1187-96.

• Genome-wide association study (GWAS) of IgA nephropathy in 20,612 individuals of European and East Asian ancestry.

• Multiple risk alleles, most associated with maintenance of the intestinal epithelial barrier and response to mucosal pathogens, including risk of inflammatory bowel disease.

• The risk alleles suggest host-intestinal pathogen interactions in establishing genetic susceptibility to IgAN.

IgA nephropathy probably can be caused by multiple different etiologies and pathogenic processes:

1) abnormally glycosylated IgA

2) antibodies against abnormally glycosylated IgA

3) reduced clearance of circulating IgA complexes

4) increased affinity for or reduced clearance of IgA deposits from the glomerular mesangium

5) excessive IgA antibody production in response to mucosal antigen exposure

6) increased permeability of mucosa to antigen

7) combinations of these factors

Aberrant glycosylation of IgA1 may be caused by genetically determined aberrant mucosal immune responses to infections.