HSP-65, An Autoantigen for Plaque Development or Plaque Vulnerability?

Editorial Slides VP Watch – December 11, 2002 - Volume 2, Issue 49

Yehuda Shoenfeld, MDSheba Medical Center, Tel Hashomer,Israel

A large number of studies have been reported on associations of coronary artery disease (CAD) in human and certain persistent bacterial and viral infections. 1

In 1978, Fabricant et al showed that experimental infection of germ-free chickens with an avian herpes virus induces arterial disease that resembles human atherosclerosis. 2

Atherosclerosis as an Autoimmune Disease

Autoantigens:

- Oxidized LDL - Heat Shock Protein 65 - 2 Glycoprotein I

- ???

Traditional Framingham risk factors fail to fully account for accelerated atherosclerosis in systemic lupus erythematosus. 3

Criteria Needed to Establish An Autoimmune Etiology. Witebsky-Rose criteria 4

It should be possible to:1. Demonstrate immunological reactivity to a self-antigen.

Characterize or isolate the inciting autoantigen.2. Induce immunological reactivity against that same antigen by

immunization of experimental animals.3. Show pathological changes (similar or identical to those

found in human disease) in the appropriate organs/tissues of an actively-sensitized animal.

4. As in 4 but following passive transfer of auto-Abs or auto-reactive T cells.

Human heat shock proteins (HSPs) are expressed on endothelial cells in response to stressors such as hypertension, smoking, lipoproteins - etc. 5

HSPs offer a target for autoimmunity under such circumstances. 5

Anti-HSP-65 and Atherosclerosis

Carotid atherosclerosis Coronary heart disease Myocardial infarction Arteriosclerosis Coronary angioplasty Myocardial infarction

Expression Of Heat Shock Protein-70 By Dendritic Cells

In early intimal lesions, HSP70 is over-expressed exclusively by dendritic cells, which suggests that dendritic cells might be involved in the early phases of atherogenesis. 6

T Lymphocytes in atheroma

20% of the infiltrating inflammatory cells are T-lymphocytes. 6, 7

T- lymphocytes are in an activated state; memory cells, CD4+ TCRab +. 6, 7

Enhanced fatty formation in C57BL/6J mice by

immunization with heat shock protein-65

Jacob George, Yehuda Shoenfeld, Arnon Afek, Boris Gilbourd, Pnina Keren, Aviv

Shaish, Juri Kopolovic, George Wick, Dror Harats

Arterioscler Thromb Vasc Biol,19:505-510,1999

Cellular and Humoral Immune Responses to Heat- Shock Protein 65 Are Both Involved In Promoting

Fatty-Streak Formation In LDL-Receptor Deficient Mice

Jacob George, Aron Afek, Boris Gilburd, Yehuda Shoenfeld, Dror Harats.

J Am Coll Cardiol 2001; 38: 900-905.

Antibodies and lymphocytes reactive to HSP65 promote fatty-streak formation in mice, providing direct evidence for the proatherogenic properties of cellular and humoral immunity to HSP65.

Adoptive transfer of 2 glycoprotein I (2GPI) reactive lymphocytes enhances early

atherosclerosis in LDL-receptor deficient mice

* Lymphocytes obtained from draining LN (mostly T cells) and splenocytes increased atherogenesis.

* Deletion of T cells prevented atherogenesis.* Ultimate evidence for autoimmunity and

immune system in atherosclerosis.* Importance of T cells in the process.

Jacob George, Dror Harats, Boris Gilburd, Arnon Afek, Aviv Shaish, Juri Kopolovic, Yehuda Shoenfeld. Circulation 102: 1822 - 1827, 2000.

AtherogenesisPlaque Rupture

Thrombosis

Infection of arterial wall- SMC proliferation associated with p53 inactivation- Local inflammation

Systemic Infection – Endothelial dysfunction due to circulating endotoxin

Classic risk factors↓ HDL Fibrinogen Triglycerides

Autoimmunity- HSP60 cross-reactivity with bacterial antigens

Systemic inflammation CRP Leukocyte count Cytokines

Adapted from: J. Danesh et al. Chronic infection and coronary heart disease: is there a link?. Lancet 350 (1997), pp. 430–436.

Postulated Mechanisms to Link Infections And Vascular Disease

As reported in VP Watch this week, Lamb et al used a BCG immunization model to assess the role of HSP in the association between infection and CAD. 7

They immunized rabbits with BCG vaccine (n=10) or saline (n=10) and subsequently fed a cholesterol diet for 10 weeks. 7

Plasma IgG specific for mycobacterial antigen A60 and human HSP-60, but not for human HSP-70, rose following BCG immunization, reaching a peak after 8 weeks. 7

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30

40

BCG Control

BCGControl

% a

ortic

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The percentage aortic area staining positively for oil red O was calculated. Each point is the mean±SE for seven rabbits. Statistical analysis was performed using unpaired t-tests. *P<0.05.

*

Effect of BCG immunization on atherosclerosis in thoracic aorta of cholesterol-fed rabbits

Lamb DJ, Ferns GA. The magnitude of the immune response to heat shock protein-65 following BCG immunization is associated with the extent of experimental atherosclerosis. Atherosclerosis. 2002 Dec;165(2):231-40.

The percentage aortic area covered by atherosclerotic plaque was greater in animals immunized with BCG compared to controls.7

The authors did not find any correlation between anti-A60 antibody titers and plaque area. 7

Conclusion:

Immunization with an HSP-containing BCG vaccine, using doses equivalent to those used for tuberculosis prophylaxis, has pro-atherogenic consequences in the cholesterol-fed rabbits.

This effect may be mediated in part by immune response directed against BCG-associated HSP.

Questions:

- Is heat shock protein 65 the main culprit autoantigen for atherosclerosis?

- Knowing the role of HSP-65 in other autoimmune diseases such as rheumatoid arthritis, how specific can HSP-65 be for atherosclerosis?

Questions:

Should we look for a single specific antigen for atherosclerosis in all patients?

Or do different antigens exist in different patients or even within the same patient?

Questions: Do you think that the role of these

autoantigens may vary at different stages of the disease? Do you think that some may contribute to plaque development and others may induce plaque complication?

Knowing that high LDL is necessary for atherosclerosis and HSP only enhances atherosclerosis, is it appropriate to say that HSP-65 may be more important in plaque complication (vulnerability) than plaque generation?

1) J. Danesh, R. Collins and R. Peto , Chronic infection and coronary heart disease: is there a link?. Lancet 350 (1997), pp. 430–436.

2) CG Fabricant, J Fabricant, MM Litrenta and CR Minick, Virus-induced atherosclerosis. J Exp Med 148 (1978), pp. 335–340.

3) Esdaile JM, et al Arthritis Rheum 2001, 44: 2311-74) Krenn V, Souto-Carneiro MM, Kim HJ, Berek C, Starostik P, Konig A, Harms H, Muller-Hermelink HK Histopathology and

molecular pathology of synovial B-lymphocytes in rheumatoid arthritis. Histol Histopathol. 2000 Jul;15(3):791-8. Review.5) George J, Harats D, Shoenfeld Y.Clin Rev Allergy & Immunol. 18: 73-86, 2000.6) Bobryshev YV, Lord RS. J Vascular Surgery 35: 368-75, 20027) A. Kinnunen et al. Scand J Immunol 2001; 54: 76-81.8) Lamb DJ, Ferns GA.The magnitude of the immune response to heat shock protein-65 following BCG immunisation is

associated with the extent of experimental atherosclerosis. Atherosclerosis. 2002 Dec;165(2):231-40.

References