Overview
This lecture covers hypersensitivity reactions, focusing on Type III reactions, their mechanisms, effects, and clinical examples.
Types of Hypersensitivity Reactions
- Hypersensitivity reactions are excessive immune responses to harmless substances, causing inflammation, tissue damage, or death.
- There are four types of hypersensitivity reactions.
- Type I involves fixed antibodies on mast cells and free-floating antigens.
- Type II involves fixed antigens on cells and free-floating antibodies.
- Type III involves immune complexes formed by antigen-antibody reactions in circulation.
Mechanism of Type III Hypersensitivity
- Type III reactions are caused by immune complexes (antigen-antibody) forming in the bloodstream.
- The immune complexes deposit in various tissues rather than causing harm where they form.
- Deposited immune complexes attract complement proteins and inflammatory cells such as neutrophils and macrophages.
- These immune cells release lysosomal enzymes, resulting in tissue inflammation and destruction.
Clinical Effects and Examples
- Common sites of immune complex deposition: blood vessels (vasculitis), kidneys (nephritis), joints (arthritis), skin (dermatitis), lungs (pneumonitis).
- Post-streptococcal infections can cause post-strep glomerulonephritis (kidney inflammation).
- Rheumatoid or reactive arthritis are linked to Type III reactions.
- Systemic lupus erythematosus (SLE) can cause arthritis, nephritis, and dermatitis via immune complex deposition.
- Serum sickness causes immune complexes to deposit in joints (arthritis), blood vessels (vasculitis), and kidneys (nephritis).
Key Terms & Definitions
- Hypersensitivity Reaction — Excessive immune response to harmless substances, causing tissue damage.
- Immune Complex — Clusters formed by antigen-antibody binding in circulation.
- Complement Proteins — Blood proteins that enhance immune responses.
- Lysosomal Enzymes — Substances released by immune cells that break down tissue.
- Vasculitis — Inflammation of blood vessels.
- Nephritis — Inflammation of the kidneys.
- Arthritis — Inflammation of joints.
- Dermatitis — Inflammation of the skin.
- Pneumonitis — Inflammation of lung tissue.
Action Items / Next Steps
- Review examples of diseases caused by Type III hypersensitivity.
- Understand the differences among the four types of hypersensitivity reactions.