Immune Response and Pathologies Overview

Key Terms

• Hypersensitivity: Immune overreaction

• Autoimmunity: Immune self-reaction

• Hyposensitivity: Immune underreaction (immunodeficiency)

Hypersensitivities Overview

Four Types of Hypersensitivities

1. Type I: Allergy

2. Type II: Antibody-mediated

3. Type III: Immune-complex

4. Type IV: Cell-mediated (T-cell)

Type I Hypersensitivity Overview

• Rapid reaction to an antigen (allergens) mediated by Immunoglobulin E (IgE).

• Varies in intensity from mild reactions (e.g., sneezing) to severe life-threatening events (e.g., anaphylaxis).

Examples

• Allergies: Symptoms include itching, swelling, and rashes.

• Atopy: Chronic local allergies (e.g., allergic rhinitis, asthma).

• Anaphylaxis: Extreme systemic reactions leading to airway obstruction and potential circulatory collapse.

• Sensitization: Initial exposure to allergens results in IgE antibody production.

Mechanism of Action

• Role of Immunoglobulins (Ig)

Types of Immunoglobulins

• IgG: Most prevalent antibody for long-term immunity.

• IgA: Found in mucosal areas, crucial for mucosal immunity.

• IgM: First antibody produced, indicating recent infection.

• IgD: Receptor on B cells, important for activation and differentiation.

• IgE: Involved in allergic reactions and parasitic infections.

Allergens

• Definition: Antigens provoking strong immediate responses.

Types of Allergens

• Inhaled: Pollen, dust mites, mold spores, animal dander.

• Ingested: Food allergens (e.g., peanuts, eggs, milk).

• Injected: Allergens from antibiotics, vaccines, insect venoms.

• Contact: Substances like latex and certain metals.

Treatment of Type I Hypersensitivity

1. Blocking Allergens

   • Medications: Antihistamines, corticosteroids, leukotriene receptor antagonists.

   • Epinephrine for severe reactions (e.g., anaphylaxis).

2. Avoidance

   • Identify allergens; implement allergen-free environments.

3. Desensitization

   • Gradual immunotherapy to promote IgG production, reducing symptom severity over time.

Type II Hypersensitivity Overview

• Antibody-mediated response (IgG and IgM) can activate the complement system.

Examples

• Transfusion reactions: Mismatched blood types causing hemolysis.

• Autoimmune diseases: (e.g., Graves' disease) where antibodies target self-antigens.

Key Concept

• Alloantigens: Self-antigens differing among individuals (e.g., ABO blood groups).

Rh Factor

• Blood Types: A, B, O, and Rh.

• Rh Factor: Present in 85% (Rh+) and absent in 15% (Rh-); complications arise during pregnancy if Rh- mother is sensitized by Rh+ blood.

Type III Hypersensitivity Overview

• Triggered when soluble antibodies react with soluble antigens to form immune complexes that lead to tissue damage.

Mechanism

• Involves immune complex reaction with IgG/IgM activating the complement pathway, causing inflammation.

Diseases

• Arthus reaction: Localized acute response after second exposure

• Serum sickness: Systemic response after exposure to specific medications.

Type IV Hypersensitivity Overview

• Delayed-type hypersensitivity mediated by T-cells against native or transplanted antigens.

Examples

• Infectious allergy: T-cell response to specific antigens (e.g., tuberculin reaction).

• Contact dermatitis: T-cell recruitment to allergens, causing rashes.

Autoimmune Disorders

• Definition: Conditions where the immune system mistakenly attacks tissues.

Causes

• Genetic Factors: MHC gene variants increase susceptibility.

• Molecular Mimicry: Microbial antigens resemble self-antigens.

• Infection: Pathogen modification of proteins creating new epitopes.

• Microbiome Changes: Influence of gut microflora on immune responses.

Examples

1. Systemic lupus erythematosus (lupus)

2. Rheumatoid arthritis

3. Myasthenia gravis

4. Multiple sclerosis.

Hyposensitivities (Immunodeficiency)

• Definition: Weakness in immune response, increasing vulnerability to infections.

Primary Immunodeficiency

• Genetic mutations present from birth affecting immune components.

Secondary Immunodeficiency

• Acquired later in life due to factors such as age, malnutrition, and medical treatments.

Examples

• B-cell defects: e.g., Agammaglobulinemia.

• T-cell defects: e.g., SCID.

Human Immunodeficiency Virus (HIV) Overview

• Type: Enveloped retrovirus targeting CD4+ T cells.

Enzymes

• Reverse Transcriptase: Converts viral RNA to DNA.

• Integrase: Integrates viral DNA into host genome.

Mechanism

• HIV targets and destroys CD4+ T cells, leading to immune system failure (CD4 count < 200 cells/µl = AIDS).

Summary of Learning Objectives

1. Sample Collection: Recognize types and factors for identification.

2. Phenotypic Testing: Explain tests relating to lab knowledge.

3. Immunological Testing: Principles of immunologic testing.

4. Genotypic Testing: Benefits of genotypic methods for diagnosis.

Conclusion

Understanding the immune system's responses, hypersensitivities, autoimmunity, and immunodeficiencies is crucial for effectively diagnosing and treating conditions involving the immune system. Collaboration across disciplines enhances public health and integrates knowledge for addressing zoonotic diseases, climate change impacts, and emerging infections effectively.