Immunology Lesson: An Easy Guide
Immunology explores how the body defends itself against pathogens. This lesson provides a deep understanding of innate and adaptive immunity, immune cells, antibodies, cytokines, hypersensitivity, autoimmunity, and immunodeficiencies. It aligns with core quiz concepts and aims to strengthen comprehension for academic success.
Innate and Adaptive Immunity
| Feature | Innate Immunity | Adaptive Immunity |
| Response Time | Immediate (minutes-hours) | Delayed (days) |
| Specificity | Non-specific | Highly specific |
| Memory | None | Long-lasting memory |
| Key Components | Skin, macrophages, NK cells | B cells, T cells, antibodies |
- Innate Immunity: First line of defense-skin, mucous membranes, phagocytes.
- Adaptive Immunity: Antigen-specific and forms memory; B cells produce antibodies, T cells kill infected cells or help others.
Immune Cells and Functions
- B cells: Mature in bone marrow. Produce antibodies. Differentiate into plasma cells and memory B cells.
- T cells: Mature in thymus. Include:
- Helper T cells (CD4+): Activate B cells and cytotoxic T cells.
- Cytotoxic T cells (CD8+): Kill infected or cancerous cells.
- Regulatory T cells: Suppress immune overactivity.
- Helper T cells (CD4+): Activate B cells and cytotoxic T cells.
- Phagocytes: Macrophages and neutrophils engulf pathogens.
- Dendritic cells: Present antigens to activate T cells.
- NK cells: Destroy virus-infected or abnormal cells.
Cytokines and Their Roles
| Cytokine | Primary Function |
| IL-2 | Promotes T cell proliferation |
| IL-4 | Stimulates B cells; class-switch to IgE |
| IL-5 | Activates eosinophils; class-switch to IgA |
| IL-8 | Attracts neutrophils to infection site |
| IL-10 | Suppresses immune response |
| TNF, IL-1 | Induce fever, inflammation |
Key Concept: IL-2 deficiency leads to poor T cell activation, causing susceptibility to viral infections.
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Antibody Structure and Classes
- Antibodies = 2 heavy + 2 light chains linked by disulfide bonds.
- Variable region: Antigen binding; Constant region: Effector functions (Fc).
| Class | Function | Location/Features |
| IgM | First antibody in response; activates complement | Blood; pentamer |
| IgG | Opsonization, crosses placenta | Most abundant; long-term memory |
| IgA | Mucosal immunity | Tears, saliva, breast milk |
| IgE | Allergy, parasite defense | Binds mast cells |
| IgD | B cell receptor | Surface of naive B cells |
Cluster of Differentiation (CD) Markers
- CD4: Helper T cells
- CD8: Cytotoxic T cells
- CD2: Present on thymocytes and NK cells
- CD19: B cell marker
If a cell has CD4, it's a helper T cell; CD8 = cytotoxic T cell.
Hypersensitivity Reactions
| Type | Mechanism | Examples |
| I | IgE-mediated, immediate | Anaphylaxis, asthma, allergies |
| II | IgG/IgM against cell surfaces | Hemolytic anemia, Rh incompatibility |
| III | Immune complex deposition | Lupus, serum sickness |
| IV | T cell-mediated (delayed) | TB test, contact dermatitis |
- Type I: Fast, involves IgE and mast cells (e.g., peanut allergy).
- Type II: IgG/IgM target body cells (e.g., Goodpasture's syndrome).
- Type III: Immune complexes lodge in tissues (e.g., SLE).
- Type IV: Delayed, T cell-mediated (e.g., poison ivy reaction).
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Autoimmune Diseases
- Systemic Lupus Erythematosus (SLE): Immune complex-mediated, more common in women.
- Rheumatoid Arthritis (RA): Joint inflammation; JRA (juvenile) involves large joints and systemic symptoms.
- Multiple Sclerosis (MS): T cell attack on CNS myelin; more frequent in females.
Estrogen impairs clearance of immune complexes-explains higher female risk of SLE.
Immunodeficiencies
| Disorder | Defect | Symptoms |
| SCID | T & B cell failure | Severe infections, failure to thrive |
| X-linked Agammaglobulinemia | No B cells (BTK mutation) | Recurrent bacterial infections after 6 months |
| Selective IgA Deficiency | IgA only | Mucosal infections, diarrhea |
| Hyper-IgM Syndrome | Class-switch defect (CD40L) | High IgM, low IgG/A, opportunistic infections |
| Job's Syndrome (Hyper-IgE) | STAT3 mutation | Eczema, staph abscesses, high IgE |
| Wiskott-Aldrich Syndrome | WAS protein, X-linked | Eczema, thrombocytopenia, infections |
Vaccine and Immune Memory
- Primary Response: IgM first, then IgG. Takes days.
- Secondary Response: Faster, stronger-thanks to memory cells.
- Vaccines: Stimulate adaptive memory without disease.
- Passive Immunity: From mom (IgG, placenta; IgA, breast milk); temporary.
10. Review Questions
Which immunoglobulin is elevated in allergic reactions?
IgE
What cytokine promotes T cell growth?
IL-2
Which immune cell type kills virus-infected cells directly?
CD8+ T cells
What type of hypersensitivity is poison ivy rash?
Type IV
Which antibody crosses the placenta?
IgG
A boy has no tonsils and low antibodies-likely diagnosis?
X-linked Agammaglobulinemia
A girl has eczema, low platelets, and infections-diagnosis?
Wiskott-Aldrich Syndrome
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