Immunology: An Easy Guide to Key Concepts and Exam (USMLE) Success

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

• Innate Immunity: First line of defense-skin, mucous membranes, and 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.

• 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

Key Concept: IL-2 deficiency leads to poor T cell activation, causing susceptibility to viral infections.

Antibody Structure and Classes

• Antibodies = 2 heavy + 2 light chains linked by disulfide bonds.
• Variable region: Antigen binding; Constant region: Effector functions (Fc).

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 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).

USMLE Immunology - Part 2

Explore key concepts in immunology tailored for USMLE Part 2 preparation. This quiz covers differences in disease presentations, cytokine deficiencies, CD antigens, and specific...

Questions: 15 | Attempts: 649 | Last updated: May 19, 2025

Sample Question

Patients sharing similar clinical symptoms and disease pathology may nevertheless present differently based upon age at disease onset. Adultonset rheumatoid arthritis (RA) and juvenile rheumatoid arthritis (JRA) are both the result of infl ammatory processes. How does the presentation of JRA differ from the presentation of adult-onset RA?

JRA is simply the presence of RA that begins before the age of 21 years

Patients with JRA are less likely to have systemic symptoms, but the likelihood of high levels of serum rheumatoid factor is the same

Patients with JRA are more likely to have large joint involvement, but the likelihood of concurrent systemic symptoms is the same

Patients with JRA are more likely to have systemic symptoms and high levels of serum rheumatoid factor

Patients with JRA are more likely to have systemic symptoms and large joint involvement

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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

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

Immunology- Antigen and Antibody Structure Quiz

Take this immunology, antigen, and antibody structure quiz if you want to find out how much you can actually recall about this topic! Test your memory and your knowledge by taking...

Questions: 22 | Attempts: 25895 | Last updated: Mar 22, 2025

Sample Question

Which of the following is NOT true?

The term epitope is not synonymous with antigen

A viral protein may contain a large number of epitopes that are capable of interacting with many different specific antibodies

Immunologic receptors on T cells recognize continuous (linear) epitopes

Immunologic receptors on T cells recognize discontinuous (conformational) epitopes

Antibodies can recognize both continuous and discontinuous epitopes

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