1. Pathophysiology of Glomerulonephritis Raj Maganti Anatomic Pathology Resident March 29, 2012

2. Glomerular diseases  Glomerulonephritis - Immune mediated/Infectious/Chemical induced Clinically manifest as nephrotic syndrome – Proteinuria (lose more than 3.5 g protein/day) – Hypoalbuminemia and generalized edema – Hypercholesterolemia and hyperlipoproteinemia: compensatory hepatic change to restore colloid osmotic pressure Glomerulopathy – lacks the cellular inflammatory component. – Similar clinical manifestations  Glomerulitis: Bacterial (embolic) and viral  Glomerular Amyloidosis  Glomerular Vasculopathy  Glomerular Lipidosis: incidental in dogs; inherited hyperlipoproteinemia in cats

3. Anatomy of the Glomerulus Mesangial Cells Glomerular Capillary Lumina Urinary Space Parietal Epithelial Cells (Bowman’s Capsule)

5. 2 types of mesangial cells  Myofibroblastic type: structural & contractile  Phagocytic/inflammatory type Mesangial cells

6. Podocytes & filtration slit

7.  Composed of proteins such as Nephrin, CD2- associated protein and podocin  In humans, mutations in the genes that encode these diaphragm proteins give rise to nephrotic syndrome.

8.  Type IV Collagen  Laminin (glycoprotein)  Heparin Sulfate (negative-charged polyanion) Lamina rara externa Lamina densa Lamina rara interna capillary lumen Podocyte foot processes Endothelial cell urinary space Glomerular Basement Membrane (GBM)

9. Glomerular and Epithelial Cell Injury  Antibodies to epithelial cell antigens, with subsequent toxins, cytokines, or other factors causing injury and detachment of epithelial cells, resulting in protein leakage

10. Mediators of Glomerular injury

11.  Combination of immune complex with C3 results in solubilization and subsequent removal of the immune complex. Finnish-Landrace lambs: inherited C3 deficiency - severe glomerular disease  Excess antigens stimulate complement fixation. Leukocyte-dependent: Complement fragments (C3a, C5a, C567) - chemotactic for neutrophils. Leukocyte-independent: C5b-9- terminal membrane attack complex of complement Stimulate mesangial cells and glomerular epithelial cells to produce chemical mediators (proteases, oxidants, IL-1, PG).  Additional membrane damage through neutrophil release of proteinases, arachidonic metabolites (e.g. thromboxane), and oxidants (esp oxygen derived free radicals and H2O2). Mediators of Glomerular injury

12.  Neutrophils  Infiltrate glomerulus due to immune complex activation & complement  Release C5a and Fc-mediated immune adherance  Release lysosomal enzymes: collagenases, elastases, chymotrypsin like protease, arachidonic acid metabolites, oxygen derived free rads, vasodilator peptides and chemotactic substances for macrophages  Activated macrophages  Infiltrate glomerulus due to immune complex activation & complement & chemotatic substances produced by neutrophils  Release proteases, complement components, chemotactic factors for neutrophils, reactive oxygen metabolites, IL-1, and platelet activating factor.  Monocytes produce a procoagulant factor that activates the extrinsic coagulation pathway. Mediators of Glomerular injury

13.  Platelets  Platelets release arachidonic acid metabolites and growth factors  Interaction of platelets with complement fragments and/or damaged endothelial cells can initiate coagulation, thrombosis, and fibrinolysis.  Antiplatelet agents have beneficial effects in both human and experimental glomerulonephritis  Fibrinogen  Leak into Bowman's space and in this region are relatively inaccessible to fibrinolytic mechanisms.  Consequently fibrin in this location may stimulate epithelial cell proliferation and infiltration of macrophages. Mediators of Glomerular injury

14.  Immune mediated: Ab-Ag complex & Complement  Infectious: Bacteria and Viruses  Chemicals: Chemotherapeutic agents Types of glomerulonephritis

15. 2 mechanisms in dogs and cats:  Preformed circulating Ag-Ab complexes: Heymann’s model – anti-rat antibodies were harvested from rabbits and injected into rats  Antigen is trapped in glomerular capillary wall and circulating antibodies form complexes with them (FIP, FeLV, Dirofilaria immitis, SLE, neoplasia) The 3 rd mechanism: Formation of anti-GBM Ab  Goodpasture’s syndrome (Humans and NHP)  Abs against NC1 (Non-Collagen domain 1) of α3 of collagen type 4 Immune mediated Glomerulonephritis

16. Lumpy-Bumpy pattern (Preformed complexes/Trapped antigen Smooth linear pattern (Anti- GBM antibodies) Immunflorescence microscopy

17. Sub-endothelialAlong GBMSub-epithelial Immune complexes deposition

18.  Direct injury to glomerular endothelial and epithelial cells  Altered Renal Blood Flow (e.g. cyclosporin A)  Induction of Immune complex formation and inflammation  Some examples:  Puromycin aminonucleoside  Adriamycin  Cyclosporine A  Histamine receptor antagonists  d-penicillamine and  Procainamide Chemical Induced Glomerular Injury

19. Morphology of Glomerulonephritis

20. Glomerulonephritis Chronic Pyelonephritis Chronic Renal Failure (Interstitial Fibrosis) Common types of renal disease: gross appearance

21. The small, white, round foci in the cortex are enlarged glomeruli Subacute Glomerulonephritis

22.  Membranous GN: characterized by thickened GBM  Most common form of immune-complex GN in cats  Predominantly subepithelial deposits  Bacterial kidney disease of salmonids: Rainbow trouts with Renibacterium salmoninarum  Proliferative GN: characterized by hypercellularity  Proliferation of mesangial cells + influx of WBCs  Budgerigar fledging disease (polyomavirus)  Membranoproliferative GN: Combination of thickened GBM and proliferation of mesangial cells  Most common form of immune-complex GN in dogs  Predominently subendothelial deposits Histological patterns of Glomerulonephritis

23. Types of Membranoproliferative Glomerulonephritis  Type I: Subendothelial deposits  type II: Intramembranous dense deposits (dense deposit disease).

24. Proliferative GN – HypercellularityMembranous GN – Thickened GBM Membranoproliferative GN – Both Features Present Glomerular Sclerosis – End Stage

25. Glomerulosclerosis: Fibrosis, hyalinization or scarring of glomeruli resulting in a shrunken, hypocellular and nonfunctional structure. Glomerular synechia (synechiae): Adhesion of glomerular tufts to the Bowman's capsule Sclerosis/Hyalinization of Bowman’s capsule Global GN: Lesion affects the entire glomerulus Segmental GN: Lesion involves only a portion of the glomerulus. Histological changes in Glomerulonephritis

26. Synechia (Segmental) (Global)

27.  Glomerulosclerosis  Glomerular hypertrophy -> glomerular hypertension -> injury to podocyte and endothelial cells -> glomerulosclerosis  Tubulointerstitial fibrosis  Injured podocytes cannot proliferate -> gaps in GBM -> proteinuria -> damaging to tubular epithelium -> tubulointerstitial fibrosis  Additional tubular injury from :  Sclerotic glomeruli -> downstream tubular ischemia  Close association with glomerular inflammation Downstream changes of Glomerulonephritis

28. Embolic (bacterial) Glomerulitis  Hematogenous spread  common in neonates and animals with immunosuppression  Puppies: Streptococcus sp., E. coli  Foals: Actinobacillus equuli  Neonatal pigs: Erysipelothrix rhusiopathiae  Sheep and Goat: Corynebacterium pseudotuberculosis  Calves: Archanobacterium pyogenes; Mannheimia hemolytica

29. Dogs: Infectious Canine Hepatitis Horses: Equine Viral Arteritis Swine: Hog Cholera & Porcine Cytomegalovirus Avian: Newcastle disease Direct viral damage to glomerular endothelial cells secondary to viral replication in endothelium ICH - Intranuclear Viral Inclusions Viral Glomerulitis

30. Greyhound: Idiopathic Glomerular & Cutaneous Vasculopathy The fine white dots in the cortex (both on the capsular and cut surfaces) are glomeruli with extensive glomerular capillary thrombosis. Necrotic glomerular endothelial cells and glomerular capillary thrombosis

31. Renal amyloidosis Diffusely tan, waxy (firm), and slightly enlarged  Amyloid-  Beta-pleated sheet confirmation  Resistant to normal degradation  Serum protein AA most common (reactive product)  Initial trigger is unknown Treated w/Lugol’s Iodine followed by dilute sulphuric acid

32. Glomerular amyloidosis Congo red

33. Dog - Glomerular Amyloidosis  Glomerular amyloid most common in dogs and cattle. Deposits in mesangium and subendothelial sites.  Medullary deposits in Shar-peis and cats, especially Abyssinian. Therefore, may not see proteinuria. “The Abyssinian and Shar-pei got married at the pink amyloid wedding. Medussa attended the wedding.” Cat – Interstitial Amyloidosis Renal amyloidosis

34. Dogs: Membranoproliferative GN Samoyed hereditary glomerulopathy – X-linked trait; mutation in COL4A5 (α5 of type 4 collagen) Other breeds: Bull Terrier (autosomal dominant); English Cocker Spaniel (autosomal recessive); Bernese Mountain; Dobermann; Norwegian Elkhound Borrelia; dirofilaria; ICH (adenovirus) Cats: Membranous GN; FeLV; FIP; FIV Horse: Membranoproliferative GN; Equine infectious anemia; streptococcus equi; Herpes virus infections Pig: Membranoproliferative GN ; PCV-2 Ruminants: Membranoproliferative GN; Finnish Landrace sheep – deficiency of complement component C3 – causes impaired Complement-mediated stabilization of immune complexes Prevalence of Glomerulonephritis

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