Dr. Sandeep G. HuilgolMBBS., DNB (Int.Med)., MMedSci (Nephro)
HEYMANN NEPHRITIS• The active HN (AHN) model was originally described byHeymann et al in 1959.• By immunizing rats with an emulsion of whole rat renal cortexin complete Freunds adjuvant.• By immunizations with a crude fraction of renal cortex calledFx1A.• With purified complex of a 600-kd glycoprotein(gp600/gp330/LRP-2/megalin) with 39- to 45-kd receptor-associated protein (RAP).• Purified megalin without RAP• A small (60 kd) N-terminal proteolytic fragment of nativemegalin.
• This highlights that a single auto-antigen or even a smallfragment of it that contains the immuno-dominant epitopes caninduce a full spectrum of MN including the nephrotic syndrome,• After immunization with any of these antigen preparations therats develop serum autoantibodies to megalin within 2 weeks,• Typical immune deposits of MN in glomeruli appear at 3 to 4weeks,• Proteinuria at 6 to 8 weeks,• A nephrotic syndrome at about 12 weeks.• Once established, the proteinuria persists until the rats die atabout 12 to 15 months of age, usually from infections orcomplications of the nephrotic syndrome.
PASSIVE HEYMANN NEPHRITIS• The passive HN (PHN) model is induced by injecting normalrats with a heterologous antiserum to rat Fx1A14 or antiserumto rat megalin.• In the former, typical glomerular deposits of MN can be seenwithin minutes, with proteinuria developing between 4 and 7days after the injection.• This phase of disease has been called the heterologous phasebecause it results from the glomerular deposits formed by theheterologous antibody.• The heterologous phase is followed in 2 to 4 weeks by theautologous phase when glomerular deposition of rat IgG(directed against the injected heterologous IgG) andworsening of proteinuria are noted.
ORIGIN OF THE ORGAN-SPECIFICAUTOIMMUNITY CONCEPT• AHN model could not be induced by immunizationswith homogenates of the other rat organs (liver,muscle, lung),but could be induced in a unilaterallynephrectomized rat with the rats own kidney.• This concludes that the disease has an autoimmunebasis and therefore called autoimmune nephrosis.
• Glassock et al in 1968 noted that although thedisease could be induced equally well with either rator human Fx1A, only the rat but not the humanantigen in FX1A could be detected in the glomerulardeposits whether the rats were immunized with rator human Fx1A.• This observation supported the concept thatantibodies in AHN were directed against autologousrenal antigens.
• MN is occasionally present as a seconddisease in patients who had another organ-specific autoimmune disease.• Suggesting autoimmune disease.
• It also is possible that such cases of MN are, in fact, of thesecondary variety and result from immune complexes and/orantigens released by immune damage in the first organ.• In that instance, the released immune complexes coulddissociate in glomerular capillaries and re-associate in thesubepithelial space, or form with released antigens that wereplanted in the subepithelial space in glomeruli.
• The definition of pathology features in Heymann nephritisrepresented a breakthrough in research of renalautoimmunity.• In spite of some components detected in human MGN (i.e.C5b-9, clusterin), Heymann nephritis could not be utilized as adirect model of human MGN because megalin is not presentin human glomeruli.• Moreover, many years later, it was described that megalinstructural homolog, the LDL-receptor, is not recognized bycirculating IgG4 in human MGN.
SITE OF AUTOANTIGENS IN THEGLOMERULUS• Heymann believed that the subepithelial deposits inAHN resulted from the binding of autoantibodies to afixed tissue antigen in the glomerulus and not fromcirculating immune complexes.• Studies in the PHN model by Van Damme et al andCouser et al showed that perfusion of a bloodlesskidney (thus excluding circulating antigen andimmune complexes) with heterologous anti-Fx1Aantiserum led to the formation of the subepithelialdeposits,• Supporting the idea that complexes in glomerulus were formed in situ by reaction withantigen present in that location rather than arriving there from circulation as preformedantigen–antibody complexes
• It is now established that the fixed tissue autoantigenHeymann speculated about is indeed present in theglomerulus, and is a 600-kd podocyte membraneglycoprotein (variously named as gp600, gp330, LRP-2, and megalin).• However Megalin could not be found in Humanglomerulus.
NEONATAL MGN• Antibodies against neutral endopeptidase was first recognizedin a newborn presenting with congenital nephrotic syndrome.Renal histology demonstrated MGN.• The basis of the pathogenesis was the mother, carrying agenetic deficiency of neutral endopeptidase because of anhomozygous deletion in MME, the corresponding gene.• She became alloimmunized against neutral endopeptidaseduring a prior pregnancy, ended with miscarriage.• Anti- neutral endopeptidase antibodies were then transferredto the fetus during the successive pregnancy and congenitalMGN developed in the newborn while disappearingthereafter.
SEARCH FOR AUTOANTIBODIES INSERUM TO PODOCYTE ANTIGENS• Salant et al sieve-isolated glomeruli by absorptionon an anti-human IgG affinity column.• Detecting a protein in the region of 185 kdreacting with sera from 26 of 37 patientsparticipating in their study in Boston.• Later, they confirmed their findings in 15 of 19patients from another geographic location (TheNetherlands).• Proteomic analysis of the reactive band identifiedthe protein phospholipase A2 receptor (PLA2-R)from the database of human proteins.
• Prunotto et al from Italy, using cultured human podocytesinstead of sieve-isolated human glomeruli, and proteomicanalysis from two-dimensional gel blots, identifiedautoantibodies to aldose reductase (AR) and manganesesuperoxide dismutase (SOD2) in sera of patients withidiopathic MN.• AR and SOD2 also could be shown by immunofluorescencemicroscopy on membrane of cultured podocytes.• The reactive autoantibodies are predominantly or exclusivelyIgG4, a subclass that does not activate complement.
Mesangio Proliferative Glomerulo Nephritis• Model for the study of mesangial proliferation has been theanti-thymocyte (anti-Thy-1) model.• Antibody to thymocytes (ATS) is reactive to a surface Thy-1antigen present on rat mesangial cells.• Administration of ATS induces a complement-dependentmesangiolysis followed by a rapid mesangial proliferativeglomerulonephritis that peaks within 5 days afterinjection, and then resolves over time .• Roles for PDGF, TGF and FGF in the pathogenesis ofproliferation and matrix synthesis during disease progressionidentified.
• Moreover, the model has been used for theinvestigation of inflammatory response to glomerularinjury.• Mesangial cell apoptosis also occurs early and late inthe disease and the model has been used to studyprogrammed cell death in kidney disease.
Anti-GBM disease (Masugi Model)• Administration of antibodies to whole glomerulior to isolated glomerular basement membrane(GBM) induces a glomerulonephritis involvingearly leukocyte adhesion molecules in regulatingneutrophil and platelet localization;proteases, reactive oxygen species andeicosanoids mediating injury in augmenting theseprocesses leading to a crescenticglomerulonephritis and interstitial nephritis .
OTHER MODELS• Wistar Kyoto models is to study CresenticGlomerulonephritis, similar to Masugi NephritisModel.• Glomerular Injury can also be studied inDomestic Cats and the Iberian Lynx.• C6-deficient PVG rats incapable of forming C5b-9also develop massive proteinuria followinginjection of antisera, suggesting that complementindependent mechanisms may also exist in MNmodels
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