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Molecular dissection of the Goodpasture epitope

Hellmark, Thomas LU (1999)
Abstract (Swedish)
Popular Abstract in Swedish

Den viktigaste funktionen för kroppens immunförsvar är att försvara oss mot främmande ämnen, t.ex. bakterier eller virus. Detta försvar är väldigt kraftfullt och interaktioner mellan ett par molekyler kan snabbt komma att omfatta miljontals molekyler och celler. En urspårad inflammatorisk process kan mycket snabbt komma att förstöra kroppens egen vävnad och därför finns det åtskilliga kontrollsystem som har till uppgift att hålla immunsystemet i schack. Trots alla dessa kontrollsystem händer det att immunsystemet angriper kroppens egna vävnader. Detta kallas för autoimmunitet. Några välkända exempel på autoimmuna sjukdomar är MS, SLE, reumatisk artrit och ungdomsdiabetes.



Många... (More)
Popular Abstract in Swedish

Den viktigaste funktionen för kroppens immunförsvar är att försvara oss mot främmande ämnen, t.ex. bakterier eller virus. Detta försvar är väldigt kraftfullt och interaktioner mellan ett par molekyler kan snabbt komma att omfatta miljontals molekyler och celler. En urspårad inflammatorisk process kan mycket snabbt komma att förstöra kroppens egen vävnad och därför finns det åtskilliga kontrollsystem som har till uppgift att hålla immunsystemet i schack. Trots alla dessa kontrollsystem händer det att immunsystemet angriper kroppens egna vävnader. Detta kallas för autoimmunitet. Några välkända exempel på autoimmuna sjukdomar är MS, SLE, reumatisk artrit och ungdomsdiabetes.



Många autoimmuna sjukdomar drabbar i något stadium njurarna. Eftersom njurarna är livsviktiga organ är detta mycket allvarligt. Njurarnas viktigaste funktion är att rena blodet från metaboliska restprodukter och att se till att blodets fysiologiska och kemiska samansättning bibehålls. Detta åstadkommes genom att blodet filtreras i njurens funktionella enheter som kallas nefron. Det finns cirka en miljon nefron i varje njure. Blodet pumpas där in i ett nystan av små kärl, en struktur som kallas glomeruli, och vatten och små molekyler kan passera genom kärlväggen. Kärlväggen i glomeruli fungerar allstå som ett filtrerings membran och består av tre lager. På insidan av kärlet sitter ett lager av endotelceller. Mitt i kärlväggen finns ett membran som kallas det glomerulära basalmembranet och ytterst finns ytterligare ett lager av celler, s.k. podocyter. En inflammation i njuren kallas för nefrit och en inflammation i glomeruli kallas följaktligen för en glomerulonefrit



Goodpastures syndrom är en autoimmun sjukdom, som uppstår genom att antikroppar bildas mot en kroppsegen struktur, nämligen basalmembranet i njuren och lungan. Dessa autoantikroppar binder in till basalmembranen och startar en kraftig inflammation som leder till att patienten får en mycket snabbt förlöpande glomerulonefrit och ibland svåra lungblödningar. Goodpastures syndrom är en ovanlig, men mycket allvarlig autoimmun sjukdom, med ca ett fall per miljon invånare och år. Obehandlad leder sjukdomen oftast till döden inom dagar till veckor. Trots en mycket aggressiv behandling med cytostatika kombinerat med avlägsnande av antikroppar från blodbanan, är det fortfarande få patienter som överlever med en bevarad njurfunktion. I vår undersökning klarade bara ungefär 20% av patienterna sig med en bibehållen njurfunktion, medan ca 40% hade avlidit och lika många behandlades med dialys sex månader efter det att sjukdomen upptäckts. Den aggressiva behandlingen har många svåra biverkningar, som t.ex. ett kraftigt försvagat immunförsvar, en ökad cancerrisk och i värsta fall kan behandlingen i sig leda till döden. (Less)
Abstract
Goodpasture disease is a prototype autoimmune disease that is characterized by a rapidly progressive glomerulonephritis, with or without lung haemorrhage, associated with autoantibodies against the glomerular basement membrane. The major antigen has previously been shown to be the non-collagenous domain of the a3 chain of type IV collagen, one of the six known a chains of type IV collagen. On average, one percent of the total IgG fraction from the patients is comprised of anti-type IV collagen autoantibodies. Ninety percent of these antibodies are a3(IV)-specific and the remaining ten percent are low-affinity antibodies, showing cross-reactivity with the other a(IV) chains. Furthermore, the epitope specificity seems to be limited, as shown... (More)
Goodpasture disease is a prototype autoimmune disease that is characterized by a rapidly progressive glomerulonephritis, with or without lung haemorrhage, associated with autoantibodies against the glomerular basement membrane. The major antigen has previously been shown to be the non-collagenous domain of the a3 chain of type IV collagen, one of the six known a chains of type IV collagen. On average, one percent of the total IgG fraction from the patients is comprised of anti-type IV collagen autoantibodies. Ninety percent of these antibodies are a3(IV)-specific and the remaining ten percent are low-affinity antibodies, showing cross-reactivity with the other a(IV) chains. Furthermore, the epitope specificity seems to be limited, as shown by monoclonal antibody inhibition. To test the hypothesis that only antibodies against certain epitopes are nephrotoxic, clinical and serological data from 77 anti-GBM positive patients were retrieved. The results showed that the anti-a3(IV) titre, and especially the antibodies that can be blocked using a monoclonal antibody, correlated with the outcome, in terms of kidney survival. Thus, the study strongly indicates the pathogenic role of the circulating autoantibodies. Epitope mapping of the anti-GBM antibodies has been done using overlapping synthetic peptides. The epitope specificity of the autoantibodies from one patient with anti-a1(IV) antibodies was revealed, and reactivity in ELISA was successfully blocked using a four-amino-acid-long peptide from the a1(IV) sequence. The same approach did not show any reactivity with the anti-a3(IV) autoantibodies. By using recombinant antigens expressed in a human cell line as chimeric proteins, where the a3(IV) sequence was exchanged for the corresponding sequence from the a1(IV) chain, we could show that only autoantibodies against the N-terminal third of the a3(IV) chain correlated with disease. The reactive sequence was further narrowed down to nine discontinuous amino acid residues. A chimeric protein comprised of a1(IV), but with these nine positions expressed as a3(IV), bound the toxic autoantibodies with approximately the same affinity as native a3(IV).



These studies provide evidence that only autoantibodies against a very limited region of the a3(IV) chain carry a toxic potential. Furthermore, epitope spreading is relatively limited, thus indicating a possibility for new forms of therapy, including epitope immunomodulatory treatment. In the future, therapy might be adjusted for each individual patient, on the basis of diagnostic tests, e.g., regarding the fine specificity and titre of the autoantibodies, thereby minimising unnecessary discomfort caused by the side effects of immunosuppressive treatment. (Less)
Please use this url to cite or link to this publication:
author
opponent
  • Prof Rees, AJ, University of Aberdeen
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Urologi, autoimmune, anti-GBM nephritis, glomerulonephritis, nephrology, Urology, nefrologi
pages
112 pages
publisher
Department of Nephrology, Lund University
defense location
Segerfalkssalen, BMC
defense date
1999-03-12 13:15
external identifiers
  • Other:ISRN: LUMEDW/(MENM-1018)-SE
ISBN
91-628-3320-0
language
English
LU publication?
yes
id
14c59c35-1e90-4bfb-98c7-8740d8354aa0 (old id 39320)
date added to LUP
2007-08-01 13:45:27
date last changed
2016-09-19 08:45:10
@misc{14c59c35-1e90-4bfb-98c7-8740d8354aa0,
  abstract     = {Goodpasture disease is a prototype autoimmune disease that is characterized by a rapidly progressive glomerulonephritis, with or without lung haemorrhage, associated with autoantibodies against the glomerular basement membrane. The major antigen has previously been shown to be the non-collagenous domain of the a3 chain of type IV collagen, one of the six known a chains of type IV collagen. On average, one percent of the total IgG fraction from the patients is comprised of anti-type IV collagen autoantibodies. Ninety percent of these antibodies are a3(IV)-specific and the remaining ten percent are low-affinity antibodies, showing cross-reactivity with the other a(IV) chains. Furthermore, the epitope specificity seems to be limited, as shown by monoclonal antibody inhibition. To test the hypothesis that only antibodies against certain epitopes are nephrotoxic, clinical and serological data from 77 anti-GBM positive patients were retrieved. The results showed that the anti-a3(IV) titre, and especially the antibodies that can be blocked using a monoclonal antibody, correlated with the outcome, in terms of kidney survival. Thus, the study strongly indicates the pathogenic role of the circulating autoantibodies. Epitope mapping of the anti-GBM antibodies has been done using overlapping synthetic peptides. The epitope specificity of the autoantibodies from one patient with anti-a1(IV) antibodies was revealed, and reactivity in ELISA was successfully blocked using a four-amino-acid-long peptide from the a1(IV) sequence. The same approach did not show any reactivity with the anti-a3(IV) autoantibodies. By using recombinant antigens expressed in a human cell line as chimeric proteins, where the a3(IV) sequence was exchanged for the corresponding sequence from the a1(IV) chain, we could show that only autoantibodies against the N-terminal third of the a3(IV) chain correlated with disease. The reactive sequence was further narrowed down to nine discontinuous amino acid residues. A chimeric protein comprised of a1(IV), but with these nine positions expressed as a3(IV), bound the toxic autoantibodies with approximately the same affinity as native a3(IV).<br/><br>
<br/><br>
These studies provide evidence that only autoantibodies against a very limited region of the a3(IV) chain carry a toxic potential. Furthermore, epitope spreading is relatively limited, thus indicating a possibility for new forms of therapy, including epitope immunomodulatory treatment. In the future, therapy might be adjusted for each individual patient, on the basis of diagnostic tests, e.g., regarding the fine specificity and titre of the autoantibodies, thereby minimising unnecessary discomfort caused by the side effects of immunosuppressive treatment.},
  author       = {Hellmark, Thomas},
  isbn         = {91-628-3320-0},
  keyword      = {Urologi,autoimmune,anti-GBM nephritis,glomerulonephritis,nephrology,Urology,nefrologi},
  language     = {eng},
  pages        = {112},
  publisher    = {ARRAY(0x7ca4580)},
  title        = {Molecular dissection of the Goodpasture epitope},
  year         = {1999},
}