Plasma Autoantibodies (Disease Associations)

Autoimmune disease can be either organ-specific illnesses, e.g. thyroid disease, type 1 diabetes, and myasthenia gravis (MG), or systemic illnesses, such as rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). The cause of autoimmune damage may be mainly due to either autoantibodies or autoimmune T lymphocytes. Nearly all autoimmune diseases are associated with circulating autoantibodies, which may also be found associated with non-related illnesses and in healthy individuals. Autoantibodies are often detected many years before the onset of disease.¹

Antinuclear antibodies

• Antinuclear factor (ANF):
  • Raised ANF is almost always present in SLE.
  • It is also associated with: drug-induced lupus erythematosus (LE), systemic sclerosis, scleroderma, Sjogren's syndrome, polymyositis, dermatomyositis, mixed connective tissue disorder and autoimmune hepatitis.
  • Drugs associated with drug-induced LE are isoniazid, phenytoin, hydralazine, methyldopa, chlorpromazine, penicillamine and minocycline.
  • Raised ANF may also be seen in Addison's disease, idiopathic thrombocytopenic purpura (ITP), Hashimoto's thyroiditis, autoimmune haemolytic anaemia, type I diabetes mellitus (DM), and occasionally a positive ANF is found in normal elderly people.²
• Single-stranded DNA antibody: 70% of patients with SLE, but also in other autoimmune rheumatic and inflammatory conditions and is therefore of limited clinical value.
• Anti-double stranded DNA antibody (anti-dsDNA): associated with SLE. It is a less sensitive but more specific test than antinuclear factor and is rarely positive in other conditions. It correlates with disease activity.
• Anti-histone antibodies: associated with SLE and drug-induced LE.
• Anti-Sm (Smith): very specific but relatively insensitive for SLE. It is associated with central nervous system involvement and nephritis in SLE.
• Anti-RNP: mixed connective tissue disease. It is specific for SLE but lacks sensitivity. Anti-RNP is also associated in a minority of patients with systemic sclerosis and scleroderma.
• Anti-Ro: primary Sjögrens syndrome, SLE.
• Anti-LA: primary Sjögrens syndrome, SLE.
• Centromere: scleroderma, systemic sclerosis.
• Nucleolar:
  • Nucleolar RNA: systemic sclerosis
  • Scl-70: diffuse cutaneous systemic sclerosis (dcSSc)
  • PM/Scl: polymyositis, systemic sclerosis overlap syndrome
• Cytoplasmic:
  • Jo-1 (an aminoacyl-tRNA synthetase antibody): dermatomyositis
  • Ribosomal-P: SLE (often in absence of anti-DsDNA antibodies)

Rheumatoid factor

• Rheumatoid factor is a significant serological marker for RA but is a poor marker for monitoring disease.
• High levels are associated with RA and Sjögren's syndrome.
• Other disease associations include chronic hepatitis, chronic viral infection, tuberculosis, leprosy, leukaemia, dermatomyositis, infectious mononucleosis, systemic sclerosis and SLE.
• IgM rheumatoid factor is found in 2-10% of healthy adults.

Anti-phospholipid antibodies

• Anticardiolipin antibodies are the most commonly detected antiphospholipid antibodies.
• Anticardiolipin antibodies are associated with primary antiphospholipid syndrome. They are also present in some patients with SLE.
• IgG anticardiolipin antibodies are more significant than IgM anticardiolipin antibodies.

• Intrinsic factor antibodies:
  • Very specific and virtually diagnostic for pernicious anaemia but sensitivity is only 40-75%.
• Parietal cell antibodies:
  • Associated with autoimmune gastritis but are also found in pernicious anaemia, autoimmune hepatitis and chronic liver disease.
  • Parietal cell antibodies may also be found in elderly patients without autoimmune disease.
• IgA anti-tissue transglutaminase (tTG), Anti-gliadin and Endomysial antibodies (EMA):
  • These are sensitive and specific for coeliac disease.
  • IgA Anti-tissue transglutaminase (tTG) are slowly replacing IgA endomysial antibodies (EMA) as the method of choice for screening for coeliac disease (high sensitivity and specificity for both coeliac disease and dermatitis herpetiformis).
  • tTG is an intracellular enzyme which is the major autoantigen of anti-endomysial antibodies (anti-EMAs). The IgG equivalents of these tests are less specific and sensitive, but may be present if the patient has IgA deficiency, which can be associated with coeliac disease.
• Anti-mitochondrial antibodies:
  • May be present in primary biliary cirrhosis (95% of patients)³, autoimmune hepatitis, other causes of cirrhosis, RA, syphilis, SLE and thyroiditis.
  • There are several different types of mitochondrial antibodies (MAs):
    • M2 anti-mitochondrial antibodies (AMAs) are found in primary biliary cirrhosis
    • M1 is associated with syphilis
    • M2 and M3 are associated with primary biliary cirrhosis
    • M6 is associated with isoniazid-induced hepatitis.
• Anti-smooth muscle antibodies:
  • High titres are found in 95% of patients with autoimmune active hepatitis.
  • May also be found with primary biliary cirrhosis, primary sclerosing cholangitis, infectious mononucleosis, primary pulmonary hypertension and 3% of healthy individuals.

Antibodies in diabetes mellitus

The presence of two or more of the following is associated with a high incidence of the development of type 1 diabetes:⁴

• Glutamic acid decarboxylase (GAD) antibody.
• Islet cell antibody: prevalence at diagnosis is 75%, first degree relatives 2-5% and general population 0.4%.
• Insulin antibody: present in 40% newly diagnosed type 1 diabetes. Titres of both islet cell and insulin antibody diminish once beta cell destruction is advanced, and are not usually detected after the first year of disease.

Thyroid antibodies

• Microsomal:
  • Combined tests for autoantibodies to thyroglobulin and thyroid microsome antigens detect almost all goitrous thyroiditis (Hashimoto's disease), atrophic thyroiditis and about 70-90% of Graves' disease.
  • Antithyroid microsomal antibodies may also be seen in patients with RA, Sjögren's syndrome, SLE and thyroid cancer.
  • Antithyroid microsomal autoantibodies are found in about 6% of normal adults and their prevalence increases with age.
• Thyroglobulin:
  • Hashimoto's thyroiditis, primary hypothyroidism, hyperthyroidism, colloid goitre, thyroid cancer, pernicious anaemia, Addison's disease and DM.
  • Also found in healthy individuals (18% in women and 5% in men).
• Thyrotropin receptor antibodies:
  • Useful in the diagnosis of Graves' disease but do not distinguish between stimulatory or inhibitory antibodies.
• Thyroid peroxidase antibodies:
  • Seen in high titre in many patients with Hashimoto's thyroiditis but also seen in intermediate titre in 50-80% of patients with Graves' disease.

Antisperm antibodies

• Specific and characteristic of immunological infertility.

Steroid cell antibodies

• Present in Addison's disease and autoimmune gonadal failure.

• Myasthenia gravis:
  • Acetylcholine receptor antibody is associated in most patients with MG.
• Antibodies in peripheral neuropathy:
  • Ganglioside M1 (GM1): patients with multifocal motor neuropathy and less frequently in Guillain-Barré syndrome (GBS).
  • Antibodies to myelin-associated glycoproteins in multiple sclerosis, MG and SLE.
• Neurological manifestations of malignancy:
  • Enteric neuronal antibodies: small cell carcinoma of bronchus.
  • Anti-neuronal nuclear antibodies (ANNA): small cell carcinoma of lung, carcinoma of breast.
  • Purkinje cell antibodies: gynaecological cancer, Hodgkin's disease.
  • Retinal antibodies: small cell carcinoma of lung.

Glomerular basement membrane antibodies:

• Are detected in untreated Goodpasture's syndrome.
• They may also co-exist with anti-neutrophil cytoplasmic antibody in patients with systemic vasculitis and rapidly progressive glomerulonephritis (RPGN).
• Concentration of GBM antibodies can be used to monitor the patient's response to therapy.

• Antineutrophil cytoplasmic antibodies (ANCA): associated with necrotising vasculitis and vasculitis associated with rheumatic and inflammatory bowel disease.
• There are two major types of indirect immunofluorescence staining:
  • C-ANCA (cytoplasmic): associated with Wegener's granulomatosis, micropolyarterits, Churg-Strauss syndrome, polyarteritis nodosa and RPGN.
  • P-ANCA (perinuclear): associated with microscopic polyangiitis, Churg-Strauss syndrome, anti-GBM disease, crescenteric glomerulonephritis and Wegener's granulomatosis.

Cardiac muscle antibodies are associated with myocarditis, idiopathic dilated cardiomyopathy and Dressler's syndrome.

• Intra-epidermal/desmosome antibody (pemphigus antibody) is associated with all forms of pemphigus.
• Basement membrane zone antibody (pemphigoid antibody) is associated mainly with bullous pemphigoid (present in 70-90% of patients).