Immunology Lecture 4: Outcomes

Immunology Lecture 4: Outcomes

• Basic anatomy of the immune system (L1): Covers organs involved in immune function, cells of the immune system, and their basic functions (white blood cells, T and B cells, antigen-presenting cells).

• Immune responses (L2-L6): Includes innate immunity (non-specific immunity), adaptive immunity (cell-mediated and antibody-mediated immunity).

• External defenses (L8): Details about external defenses of the body.

• Immune-related pathology (L7-L8): Discusses different diseases and conditions connected to the immune system, such as cancer, allergies, hypersensitivity, autoimmune disorders, transplant rejection, and HIV.

Adaptive Immunity: Lymphocytes and Antigens

• Antigens: Molecules that trigger a specific immune response.

Lymphocytes and Receptors

• B cells: Have B-cell receptors (BCRs) that bind to specific antigens.

• T cells: Have T-cell receptors (TCRs) that bind to specific antigens.

• Antigens: T-independent (polysaccharides) and T-dependent (proteins).

B Lymphocytes

• B cells differentiate into plasma cells: Produce antibodies.

• Some B cells become memory cells: Remember the pathogen for faster future responses.

B Lymphocytes Produce Antibodies

• B cells differentiate into plasma cells: Secrete antibodies.

• Some B cells become memory cells: Provide immunological memory.

• Antibody classes: Five types of immunoglobulins (Ig): IgG, IgA, IgM, IgE, IgD.

Antibodies

• Structure: Y-shaped proteins with identical antigen-binding sites, variable regions (Fab), and constant regions (Fc).

• Classes (IgM, IgA, IgD, IgG, IgE): Different classes have different functions and locations in the body.

• Biological Functions:

  • Neutralization: Block pathogen from entering cells
  • Agglutination: Clumping of cells
  • Precipitation: Making pathogens insoluble
  • Opsonization: Enhanced phagocytosis
  • Complement activation: Triggering innate immune response through complement system.

Antibodies: Hinder Pathogens

• Neutralization: Blocking pathogens.

• Agglutination/Precipitation: Making pathogens easier to remove.

Antibodies & Innate Responses: Complement System

• Activation: Antibodies activation or direct activation
• Classical Pathway: Antibody-mediated complement activation following binding to an antibody-antigen complex.
• Alternate Pathway: Direct complement activation to pathogen

Antibodies & Innate Responses: Phagocytosis

• Opsonization: Coating pathogens to enhance phagocytosis.
• Phagocytes (macrophages, neutrophils): Engulf pathogens for elimination.

Antibodies & Innate Responses: NK Cells

• Antibody-dependent cellular cytotoxicity (ADCC): Antibody-coated pathogens triggers NK cell killing.
• NK cells: Kill antibody-coated cells.

Antibody Specificity

• Huge numbers of antigens.
• Each B cell recognizes only one antigen.
• High diversity of antibody responses through genetic shuffling.

Antibody Specificity: Clonal Selection

• Diverse B cells produced, each with a unique antigen receptor.
• Antigen binding causes the specific B cell to be activated.
• Some activated B cells become plasma cells.
• Some activated B cells become memory B cells.

Antibody Specificity: Primary & Secondary Response

• Primary response: Initial antibody production after exposure to antigen.
• Secondary response: Faster and stronger antibody production upon re-exposure to the same antigen due to memory cells.

Antibodies: Active vs Passive Immunity

• Active immunity: Body produces antibodies through exposure.
• Passive immunity: Antibodies borrowed from another source (e.g., breast milk).
• Examples: IgG from mother to fetus, IgA in breast milk, clinically administered antibodies.

Vaccination

• History and development of Louis Pasteur’s vaccine: Attenuated/weakened bacteria to reduce virulence.

Explore the fundamentals of immunology in Lecture 4, focusing on the anatomy of the immune system, immune responses including innate and adaptive immunity, and immune-related pathology. Understand the roles of lymphocytes and the mechanisms behind antigen recognition and response.