What is the fundamental difference between the targets of a normal immune response and an autoimmune response?

A normal immune response targets foreign (non-self) antigens from pathogens, while an autoimmune response targets self-antigens (host glycoproteins/glycolipids) due to a failure in self-tolerance.

How does Rheumatoid Arthritis differ from Osteoarthritis in terms of its underlying cause?

Rheumatoid Arthritis is an autoimmune disease where the immune system attacks the synovial membrane of joints, whereas Osteoarthritis is a degenerative condition caused by mechanical wear and tear of the joint cartilage.

Compare organ-specific and systemic autoimmune diseases.

Organ-specific diseases (e.g., Type 1 Diabetes) involve an immune attack localized to one organ, while systemic diseases (e.g., Lupus) involve an attack on antigens found throughout the entire body.

Why is it a mistake to describe an autoimmune disease as an 'immunodeficiency'?

Immunodeficiency refers to a weakened or absent immune system that cannot fight infections, whereas autoimmunity involves an overactive, misdirected immune system that is effectively attacking the host.

What is a common misconception regarding the role of genetics in autoimmune diseases?

A common error is assuming genetics is the sole cause; however, genetics only provides 'susceptibility.' An environmental trigger or stimulus is usually required to actually initiate the disease.

Why might a patient with Rheumatoid Arthritis experience symptoms like lethargy and fever, unlike a patient with Osteoarthritis?

RA is a systemic autoimmune condition involving body-wide inflammation and the release of cytokines, which cause general symptoms like fever and fatigue, whereas OA is a localized mechanical issue.

Define 'Self-Antigen' in the context of immunology.

Self-antigens are molecules (usually glycoproteins or glycolipids) on the surface of an individual's own cells that the immune system uses to recognize the cell as 'self' rather than foreign.

What is meant by 'Susceptibility' in autoimmune research?

Susceptibility is the inherited likelihood or predisposition of an individual to develop an autoimmune disease when exposed to specific environmental pathogens or stimuli.

What are the primary immune cells involved in the attack during an autoimmune response?

The primary effectors are B-lymphocytes (which produce autoantibodies) and T-lymphocytes (both helper T-cells that coordinate the attack and cytotoxic T-cells that destroy host cells).

How do migration studies support the role of the environment in autoimmunity?

Studies show that people moving from low-prevalence areas (like Japan) to high-prevalence areas (like the USA) show increased rates of autoimmune disease, suggesting environmental factors override or trigger genetic predispositions.

Autoimmune Diseases | OCR AS-Level Biology

4. Biodiversity, Evolution & Disease

Autoimmune Diseases

Summary

Autoimmune diseases represent a failure of the immune system's ability to distinguish between 'self' and 'non-self' antigens. This leads to a chronic immune response where antibodies and lymphocytes target the body's own tissues, resulting in inflammation and functional impairment.

1. Definition & Core Concepts

Autoimmunity is a condition where the immune system mistakenly identifies the body's own molecules as foreign pathogens, initiating a destructive immune response.
Self-Antigens: These are typically glycoproteins or glycolipids located on the surface of host cells that normally signal to the immune system that the cell belongs to the body.
Loss of Self-Tolerance: The fundamental cause is the breakdown of the mechanisms that normally prevent T and B lymphocytes from reacting against self-antigens during their development.
Immune Effectors: In these diseases, both B-lymphocytes (producing autoantibodies) and T-lymphocytes (helper and cytotoxic) actively participate in damaging healthy tissues.

Diagram showing an auto-reactive T-cell attacking a host cell after misidentifying a self-antigen.

2. Underlying Principles of Pathogenesis

Genetic Susceptibility: Certain individuals inherit genes that make their immune systems more likely to fail in self-recognition, often linked to specific MHC (Major Histocompatibility Complex) variants.
Environmental Triggers: Exposure to specific pathogens, chemicals, or lifestyle factors can activate the latent genetic predisposition, leading to the onset of disease.
Molecular Mimicry: This occurs when a pathogen's antigens are structurally similar to host antigens, causing the immune system to cross-react with host tissues after the infection is cleared.
Prevalence: These conditions affect a significant portion of the population (approximately 5%), indicating that immune regulation is a complex and delicate balance.

3. Classification of Autoimmune Diseases

Organ-Specific Diseases: The immune attack is localized to a single organ or tissue type. For example, in Type 1 Diabetes, the immune system specifically targets the beta cells of the pancreas.
Systemic (Non-Organ-Specific) Diseases: The immune response is directed against antigens found throughout the body, leading to widespread damage. Systemic Lupus Erythematosus (SLE) is a classic example.
Rheumatoid Arthritis (RA): While often categorized by its primary effect on joints, RA involves systemic inflammation that can affect the lungs and heart, though it is primarily known for destroying synovial membranes.

4. Key Distinctions

5. Exam Strategy & Tips

6. Common Pitfalls & Misconceptions