Antinuclear antibodies are part of a complex diagnostic process for systemic connective tissue diseases. The complex mechanism of the formation of antinuclear antibodies makes the interpretation of their results difficult, and the presence or absence of individual antibodies does not always indicate a disease process. What are the types of antinuclear antibodies? When should the test be performed?

Contents:

  1. Antinuclear antibodies - types
  2. Antinuclear antibodies - formation and mechanism of action
  3. Antinuclear antibodies - indications for the test
  4. Antinuclear antibodies - what is the research about?
  5. Antinuclear antibodies - how to interpret the result?

Antinuclear antibodies( ANA , anti-nuclear antibodies) are autoantibodies directed against elements of the cell nucleus, eg DNA and cytoplasm. They are one of the most diverse and most studied antibodies.

Antinuclear antibodies - types

  • antibodies against extractable nuclear antigens (anti-ENA):
    • against DNA topoisomerase I (anti-Scl70)
    • against ribonucleoprotein (anti-RNP)
    • against Smith antigen (anti-Sm)
    • anti-Mi2 / Mi-2
    • anti-Ro (SS-A)
    • anti-La
    • anti-Jo1
    • anti-PM-Scl
    • anti-Kn
  • antibodies against the pore-forming protein gp-2010 (anti-gp-210)
  • antibodies against native double-stranded DNA (anti-dsDNA)
  • anti-centromeric antibodies (anti-ACA)

Antinuclear antibodies - formation and mechanism of action

Autoimmunity is an abnormal response of the immune system against its own tissues, resulting in the emergence of autoimmune diseases.

Various mechanisms of autoimmunity have been described, one of which is the release of antigens hidden from the immune system, e.g. as a result of inflammatory tissue damage.

The elements found in the cell nucleus are released, e.g. DNA, RNA, histones, which the immune system begins to recognize as foreign and produces antinuclear antibodies against them.

Antinuclear antibodies - indications for the test

  • suspected connective tissue diseases:
    • systemic lupus erythematosus (presence of antibodies in 95-100% of patients; anti-dsDNA antibodies are a specific disease marker)
    • drug-induced lupus (95-100% of patients)
    • antiphospholipid syndrome (40-50% of patients)
    • systemic sclerosis (80-95% of patients, especially anti-Scl70 antibodies)
    • polymyositis and dermatomyositis (40-80% of patients, especially anti-Jo1 and anti-Mi2 antibodies)
    • Sjögren's syndrome (48-96% of patients, especially anti-Ro and anti-La antibodies)
    • rheumatoid arthritis (about 10% of patients)
    • juvenile idiopathic arthritis (less than 10% of patients)
    • Raynaud's syndrome (20-60% of patients)
    • fibromyalgia (15-25% of patients)
    • mixed connective tissue diseases (95-100% of patients)
  • assessment of disease activity and monitoring of treatment effectiveness, e.g. anti-dsDNA antibodies in systemic lupus
  • correlating the presence of antibodies with the occurrence of specific symptoms of the disease, e.g. Sjögren's syndrome and the presence of anti-Ro and anti-La antibodies
  • prognosing disease in the future

Antinuclear antibodies - what is the research about?

Blood taken from the elbow bend in an empty stomach is used to determine antinuclear antibodies.

The methods for determining the antibodies are very different and depend on the type of antinuclear antibody that is being tested. These are mainly immunological methods such as:

  • ELISA
  • RIA
  • indirect immunofluorescence
  • double immunodiffusion method
  • western blot

In the case of antinuclear antibodies, a two-stage diagnosis is used. First, a screening test is performed using the highly sensitive indirect immunofluorescence method.

The indirect immunofluorescence method consists in immobilizing HEp-2 cells derived from human epithelial cells on a microscope slide.

Cells of this line have antigens in their cytoplasm and nucleus that bind pathological antibodies from the patient's blood.

After adding the patient's serum to the slide, the antinuclear antibodies bind with specific antigens and are visible under the microscope thanks to special fluorescent markers.

The advantage of indirect immunofluorescence is the ability to differentiate the types of antibodies on the basis of the type of illumination of the fluorescent dye.

For example, a glowing nucleus of a homogeneous type means the presence of anti-dsDNA or anti-ssDNA.

A positive result of the screening test must always be confirmed. For this purpose, very specific immunological methods are used, e.g. western blot. After detecting the presence and identification of the type of antinuclear antibody, its titer is determined, i.e. the highest dilution of the serum in which the presence of antibodies can be detected.

Antinuclear antibodies - how to interpret the result?

The correct titer of antinuclear antibodies should be below 1:40.

If the screening test for antinuclear antibodies is negative and there are no clinical symptoms suggesting systemic connective tissue disease, the diagnosis should not be extended to specific antibodies, e.g. anti-dsDNA, anti-Sm.

Clinically significant titres in adults are considered to be ≥ 1: 160, and in children ≥ 1:40.

In case of positive results, it is suggested to interpret the test result as follows:

  • titer 1: 40-1: 80 - borderline result (weakly positive), in the absence of clinical symptoms of connective tissue diseases, it is not recommended to repeat the test or perform a follow-up test, because the results in most people do not change over the years
  • titer 1: 160-1: 640 - medium positive result, in the absence of clinical symptoms of connective tissue diseases, it is recommended to repeat the test after 6 months
  • titer ≥ 1: 1280 - high positive result, in the presence of clinical symptoms of connective tissue diseases, further specialist diagnosis is required to diagnose the disease

It should be noted that serological testing for antinuclear antibodies is part of a complex diagnostic process, and a positive result must always be interpreted in the context of the clinical picture and the presence of the characteristic symptoms of the disease.

Low titer antinuclear antibodies are present in 5% of the he althy population and their frequency increases with age.

Additionally, their presence is found in physiological and pathophysiological states in which antinuclear antibodies have no diagnostic significance:

  • infections e.g. tuberculosis, syphilis, malaria
  • liver diseases e.g. cirrhosis
  • lung diseases e.g. sarcoidosis, asbestosis
  • cancer e.g. leukemia, lymphoma, breast cancer, melanoma
  • skin diseases e.g. psoriasis, lichen planus
  • after organ transplant e.g. heart transplant, kidney transplant
  • use of drugs, e.g. antiepileptic drugs, hydralazine, lithium s alt,
  • other autoimmune diseases, e.g. Hashimoto's disease, Addison's disease, type I diabetes
  • pregnancy(up to 20% of pregnant women)
Worth knowing…

The emergence of different types of antinuclear antibodies is characterized by ethnic variability.

For example, Caucasian patients with systemic sclerosis are more likely to have anti-ACA antibodies, and African Americans and African Americans are more likely to have topoisomerase-reactive antibodies.

About the authorKarolina Karabin, MD, PhD, molecular biologist, laboratory diagnostician, Cambridge Diagnostics Polska A biologist by profession, specializing in microbiology, and a laboratory diagnostician with over 10 years of experience in laboratory work. A graduate of the College of Molecular Medicine and a member of the Polish Society of Human Genetics. Head of research grants at the Laboratory of Molecular Diagnostics at the Department of Hematology, Oncology and Internal Diseases of the Medical University of Warsaw. She defended the title of doctor of medical sciences in the field of medical biology at the 1st Faculty of Medicine of the Medical University of Warsaw. Author of many scientific and popular science works in the field of laboratory diagnostics, molecular biology and nutrition. On a daily basis, as a specialist in the field of laboratory diagnostics, he runs the content department at Cambridge Diagnostics Polska and cooperates with a team of nutritionists at the CD Dietary Clinic. He shares his practical knowledge on diagnostics and diet therapy of diseases with specialists at conferences, training sessions, and in magazines and websites. She is particularly interested in the influence of modern lifestyle on molecular processes in the body.

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