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Autoimmune Diseases

For medical students2 min readUpdated 2026-10-10

Autoimmune diseases represent a broad group of pathological conditions driven by an abnormal immune response directed against the body's own self-antigens. The primary etiologic factor is the loss of natural self-tolerance, causing the immune system to attack and destroy native tissues. Understanding these processes is a core component of modern pathology and medicine.

Core PathologyDevelopment of an aggressive immune response directed exclusively against self-antigens.
Age FactorIn older populations, autoantibodies are frequently detected in completely healthy individuals.
Primary CauseThe underlying etiology of all such diseases is the loss of immune self-tolerance.
Physiological NormA normal baseline immune response is vital for recognizing self-antigens.

Physiological Aspects and Baseline Norm

In pathology, it is important to recognize that the production of autoantibodies is not always a sign of disease. Under normal physiological conditions, the human immune system interacts with native tissues without causing destruction.

Autoantibodies can be detected in the serum and tissues of completely healthy individuals, a phenomenon particularly common in older age groups. These antibodies perform an important physiological function: they form after tissue injury and are essential for the efficient clearance of cellular debris. Furthermore, a normal, physiologically adequate immune response is critical for proper recognition of major histocompatibility complex (MHC) self-antigens, preventing pathological aggression against healthy cells.

Three Hallmark Criteria of Autoimmune Pathology

Classifying a condition as an autoimmune disease requires more than simply detecting antibodies in the blood. Diagnosis is based on a strict triad of criteria:

  1. Presence of an autoimmune reaction. Documentation of immune activity directed against self-antigens.
  2. Primary pathogenetic significance. Clinical and experimental data confirming that this specific reaction drives the disease rather than being a secondary consequence.
  3. Exclusion of other causes. The condition must lack any other identifiable etiology capable of fully explaining the observed clinical picture.

Only when all three criteria are met is a pathology considered truly autoimmune.

Classification by Target Specificity

Depending on the structural targets of autoantibodies, autoimmune diseases are divided into three main groups:

Etiology

The fundamental trigger for any autoimmune disease is the loss of self-tolerance. Under normal conditions, the immune system is tolerant to native tissues; when this property is lost, self-cells are recognized as foreign antigens, leading to their destruction. This breakdown in recognition underlies the pathogenesis of all diseases in this group, regardless of whether a single organ or the entire body is affected.

Mnemonic

To quickly remember the classification, use the trio OSI: Organ-specific (single organ, local), Systemic (nuclear components, whole body), Intermediate (selectively a few organs).

Frequently asked questions

Which specific antibodies against cell nuclear components are characteristic of systemic lupus erythematosus?

Systemic lupus erythematosus is characterized by a heterogeneous pool of antinuclear antibodies (ANA) targeting various intracellular structures. Specific diagnostic autoantibodies include:

  • Anti-double-stranded DNA (anti-dsDNA) antibodies — highly specific for SLE, found in 20–70% of patients.
  • Anti-histone antibodies — found in most patients and serve as a marker for drug-induced lupus.
  • Anti-Sm (Smith) antibodies — directed against ribonucleoprotein complexes (small nuclear ribonucleoproteins) and exhibit very high diagnostic specificity.

The screening pool also includes autoantibodies to nucleoli and centromeres.

What pathogenetic mechanisms lead to the loss of immune self-tolerance?

The loss of self-tolerance is driven by a combination of central and peripheral mechanisms. Key pathogenetic processes include:

  • Defects in central tolerance — failures in negative selection of T cells in the thymus.
  • Defects in peripheral tolerance — deficiency of regulatory T cells (Tregs), inflammation, and polyclonal activation.
  • Molecular mimicry — cross-reactive immune responses due to structural similarities between microbial and self-antigens.
  • Modification of self-antigens — protein structural changes induced by infectious agents or denaturation.
  • Release of sequestered antigens — exposure of intracellular proteins that normally never contact the immune system.
  • Production of anti-idiotypic antibodies and stimulation via innate immune receptors.
Which conditions are classified as organ-specific autoimmune diseases besides Hashimoto's thyroiditis?

Organ-specific autoimmune diseases, where the immunopathological process is restricted to a single tissue or organ, include:

  • Atrophic gastritis.
  • Type 1 insulin-dependent diabetes mellitus — characterized by the destruction of pancreatic islet β-cells.
  • Autoimmune hemolytic anemia.
  • Autoimmune oophoritis — localized destruction of ovarian tissue.
What general pathological morphological changes in tissues are characteristic of autoimmune diseases?

Autoimmune and rheumatic processes share several distinct morphological tissue changes:

  • Plasmacytic transformation and lymphoid tissue hyperplasia.
  • Polyserositis.
  • Vasculitis featuring mucoid and fibrinoid swelling of the vessel walls; potential fibrinoid necrosis and vascular thrombosis.
  • In rheumatic fever — formation of characteristic perivascular Aschoff bodies (granulomas) in the stroma.
  • Sclerosis of vessels and tissues.
What is the role of major histocompatibility complex antigens in genetic predisposition to autoimmune diseases?

Major histocompatibility complex (MHC/HLA) antigens play a key role in genetic predisposition to autoimmune diseases, demonstrated by specific allele associations:

  • MHC class I (HLA-I) molecules — associated with cytotoxic T-cell-mediated disorders. For instance, the HLA-B27 allele confers a high risk of ankylosing spondylitis and acute anterior uveitis.
  • MHC class II (HLA-II) molecules — more commonly linked to autoimmune conditions such as rheumatoid arthritis, multiple sclerosis, and systemic lupus erythematosus. Goodpasture syndrome is associated with HLA-DR2.
  • Specific polymorphisms — in type 1 diabetes mellitus, an amino acid substitution at position 57 of the DQβ1 molecule is critical, while juvenile dermatomyositis is linked to HLA-DQA1*0501 and HLA-DR3 alleles.
Does the presence of autoantibodies in the blood always indicate an autoimmune disease?

No, not always. Autoantibodies can be present in the serum and tissues of healthy individuals, especially in older age groups. Their physiological role is to bind and clear debris following tissue injury.

What conditions are necessary for a pathology to be classified as autoimmune?

Three factors are required: the presence of an autoimmune reaction, confirmation of its primary pathogenetic significance (clinically or experimentally), and the complete absence of other primary causes capable of explaining the disease.

What is the difference between systemic and organ-specific autoimmune diseases?

In organ-specific diseases (e.g., Hashimoto's thyroiditis), antibodies attack only one specific organ. In systemic diseases (such as systemic lupus erythematosus), autoantibodies react with components of cell nuclei throughout the body, causing widespread multi-organ damage.

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