Overview
Autoimmunity occurs when the immune system loses its ability to distinguish "self" from "non-self" and mounts an immune response against the body's own tissue antigens. Nobel laureate Paul Ehrlich coined the term "Horror autotoxicus" to describe the body's innate aversion to attacking itself — yet in autoimmune disease, this safeguard fails.
Autoimmune diseases affect roughly 5–7% of adults, with two-thirds being female, and range from organ-specific conditions like Type 1 diabetes and Hashimoto's thyroiditis to systemic diseases like systemic lupus erythematosus (SLE) and rheumatoid arthritis. Understanding the mechanisms of self-tolerance and its breakdown is essential for diagnosing and managing these conditions in the laboratory and clinic.
Learning Objectives
After this lesson you will be able to…- Define autoimmunity and describe its history
- Classify autoimmune diseases into systemic, organ-specific, and haemolytic categories
- Describe the causes and mechanisms of self-tolerance and its breakdown
- Discuss the immunopathology of autoimmune diseases (Type II, III, IV reactions)
- Describe the LE cell phenomenon and its association with SLE
- Describe the diagnosis and treatment approaches for autoimmune diseases
Clinical Story
Why This MattersA 40-year-old woman presents with symmetric joint pain and swelling in her hands and wrists for the past several months, along with morning stiffness lasting over an hour. Her physician suspects rheumatoid arthritis and orders Rheumatoid Factor testing along with other autoimmune markers — the lab technologist's understanding of autoantibodies and immunopathology is critical to correctly performing and interpreting these tests.
Core Concepts
Associated with autoantibodies to antigens that are not tissue-specific, so multiple organs may be affected. Examples: rheumatoid arthritis (RF antibody against Fc fragment of Ig), systemic lupus erythematosus (SLE), scleroderma, Sjögren's syndrome, and polymyositis.
Autoimmunity restricted to a specific organ. Examples: Type 1 diabetes (islet cells), Hashimoto's thyroiditis (hypothyroidism), Graves' disease (hyperthyroidism), Addison's disease (adrenal glands), Goodpasture's syndrome, Multiple sclerosis, and Myasthenia gravis.
Autoantibodies against blood cells: anti-RBC antibodies cause autoimmune haemolytic anaemia, anti-platelet antibodies cause autoimmune thrombocytopenia, and anti-leucocyte antibodies cause autoimmune leucopenia.
Self-tolerance is maintained by clonal deletion (removal of self-reactive lymphocyte clones) and clonal inactivation/anergy. Breakdown can result from MHC-mediated antigen presentation abnormalities, gene mutations, environmental triggers (pathogens, drugs, hormones, toxins), complement deficiency, and molecular mimicry (e.g. rheumatic fever, where antibodies against Group A Streptococcus M protein cross-react with cardiac tissue).
Laboratory Principle
Autoimmune disease diagnosis relies on detecting circulating autoantibodies (e.g. antinuclear antibody, anti-dsDNA, Rheumatoid Factor) or characteristic cellular phenomena (e.g. LE cell) using techniques such as immunofluorescence, ELISA, and agglutination. Immunopathology of autoimmune disease involves antibody-mediated (Type II), immune complex-mediated (Type III), and cell-mediated (Type IV) hypersensitivity mechanisms, each producing characteristic tissue damage patterns that guide diagnostic test selection.
Equipment Required
Reagents & Materials
| Reagent / Material | Concentration / Grade | Purpose | Storage |
|---|---|---|---|
| Anti-dsDNA / ANA IF kit | Kit-specific (Crithidia luciliae substrate) | Detects autoantibodies against dsDNA | 4°C / freezer per kit |
| Rheumatoid Factor latex reagent | Latex-bound IgG | Detects RF (19S IgM against Fc of Ig) | 4°C |
| C-Reactive Protein reagent | Kit-specific | General inflammatory marker | 4°C |
| Anti-phospholipid antibody ELISA kit | Kit-specific | Detects antiphospholipid antibodies | 4°C per kit |
Step-by-Step Procedure
Review clinical presentation and physical examination findings to determine which autoimmune screening tests are appropriate.
Perform general tests: C-Reactive Protein, autoantibody titres (anti-DNA, anti-phospholipids), Rheumatoid Factor, and Erythrocyte Sedimentation Rate.
Order organ-specific tests as indicated — e.g. fasting glucose for suspected Type 1 diabetes, neurological examination for suspected multiple sclerosis.
Use immunofluorescence or ELISA to confirm specific autoantibodies (e.g. anti-dsDNA, anti-thyroglobulin) relevant to the suspected disease.
Correlate laboratory findings with clinical presentation before finalising the report, since autoimmune diagnosis is rarely based on a single test alone.
Flow Diagram
Quality Control
Run positive and negative controls with every autoantibody assay batch. Ensure reagents (latex RF reagent, ANA substrate slides, ELISA kits) are within expiry and stored per manufacturer instructions.
Participate in EQAS programs for autoimmune serology to ensure inter-laboratory consistency, particularly for ANA titre reporting which can vary significantly between methods.
Reference Values
Normal Ranges⚠️ Reference ranges may vary between laboratories. Always apply your laboratory's established reference intervals.
Clinical Interpretation
| Finding | Possible Significance | Action / Follow-up |
|---|---|---|
| Positive Rheumatoid Factor | Suggests rheumatoid arthritis (also seen in Sjögren's, SLE) | Correlate with joint symptoms; consider anti-CCP for specificity |
| Positive anti-dsDNA | Highly specific for SLE | Correlate with ACR/EULAR clinical criteria for SLE |
| LE cells present in bone marrow/blood | Suggests SLE (auto immune factor in plasma) | Correlate with clinical and other serological findings |
Common Errors & How to Avoid Them
Cause: Many autoantibodies (e.g. RF, ANA) can be positive in healthy individuals or unrelated conditions.
Prevention: Always interpret autoantibody results together with clinical presentation and established diagnostic criteria, not in isolation.
Cause: Some diseases (e.g. thyroid disorders) share autoantibodies but differ in tissue distribution and pathology.
Prevention: Learn the specific antigen targets and typical organ involvement of each disease.
Cause: LE cell formation requires fresh sample processing; delays reduce sensitivity.
Prevention: Process samples promptly per laboratory SOP for LE cell/buffy coat preparation.
Laboratory Tips from the Bench
Remember that a positive ANA/autoantibody screen is common in the general population — always correlate strength of titre and pattern with clinical suspicion rather than treating any positive as diagnostic.
When examining for LE cells, look in the buffy coat of peripheral blood or bone marrow — LE cells are polymorphonuclear cells that have phagocytosed nuclear material of other cells.
"SOS — Systemic, Organ-specific, and haemolytic" — remember the three broad categories of autoimmune disease with this acronym.
Important Notes
Rheumatic fever, a classic example of molecular mimicry, shows that antibodies against a pathogen (Group A Streptococcus M protein) can cross-react with self-tissue (cardiac valves/sarcolemma), causing tissue damage well after the original infection resolves.
Common strategies include immunosuppression (prednisone, cyclosporin A), plasmapheresis, thymectomy (in select Myasthenia Gravis patients), and targeted monoclonal antibodies (anti-CD4, anti-IL-2R).
Interactive Quiz
Test Your KnowledgeFlashcards
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Clinical Case Study
Apply Your KnowledgeMeera presents with symmetric swelling and pain in the small joints of both hands, morning stiffness lasting over an hour, and low-grade fatigue for the past 6 months. Her physician suspects rheumatoid arthritis and orders relevant serological testing.
A high-titre positive Rheumatoid Factor with elevated CRP and ESR, in the context of symmetric small-joint arthritis, strongly supports a diagnosis of rheumatoid arthritis. The negative anti-dsDNA helps exclude SLE as the primary diagnosis.
- →Rheumatoid Factor is a systemic (non-tissue-specific) autoantibody marker for RA.
- →CRP and ESR are general inflammatory markers that support but do not confirm a specific diagnosis.
- →A negative disease-specific marker (anti-dsDNA) helps differentiate between overlapping autoimmune conditions.
Frequently Asked Questions
Roughly two-thirds of autoimmune disease cases occur in females. The precise reasons are multifactorial and include hormonal, genetic, and X-chromosome-related immune regulation differences, though the exact mechanisms remain an active area of research.
Most autoimmune diseases are chronic and managed rather than cured — treatment focuses on suppressing the abnormal immune response and controlling symptoms using immunosuppressive drugs, plasmapheresis, and targeted biologics.
No. RF can be positive in other conditions (Sjögren's syndrome, SLE, chronic infections) and even in some healthy individuals. It should be interpreted together with clinical findings and other test results.
Quick Revision
10-Minute ReviewKey Takeaways
- Autoimmunity is the failure of the immune system to distinguish self from non-self, leading to attack on the body's own tissues.
- Autoimmune diseases are classified as systemic, organ-specific, or haemolytic based on tissue involvement.
- Self-tolerance is normally maintained via clonal deletion and inactivation, which can break down due to genetic, environmental, or infectious triggers.
- Molecular mimicry is a key mechanism, as illustrated by rheumatic fever.
- Autoimmune immunopathology involves Type II, III, and IV hypersensitivity reactions.
- Diagnosis relies on general (CRP, ESR, RF, autoantibody titres) and disease-specific tests, always interpreted alongside clinical findings.
Competency Checklist
Track Your MasteryReferences
- NIOS Microbiology Module — Lesson 64: Autoimmunity and Autoimmune Diseases.
- Ehrlich P. Historical concept of "Horror autotoxicus" (early 1900s).
- Standard textbooks of Medical Microbiology and Immunology (Ananthanarayan & Paniker; Baveja).