immune system

Immune System Overview

• Adaptive Defenses: Specialized responses that recognize specific antigens.

  • Specific: Targets specific antigens (example: flu virus).

  • Systemic: Responses are not limited to the site of initial infection.

  • Memory: Strengthened responses upon re-exposure to known antigens.

Types of Adaptive Immunity

• Humoral Immunity: Mediated by antibodies in the blood.

  • Involves B cells producing antibodies that bind to pathogens.

• Cellular Immunity: Involves T cells.

  • Directly kills infected cells or marks them for destruction.

  • Involves a respiratory burst, generating reactive oxygen species.

  • Marks target cells for destruction by phagocytes.

• Antigens: Substances that provoke immune responses.

  • Targets adaptive immunity; usually large, complex, and nonself molecules.

Antigenic Determinants

• Antigenic Determinants: Unique parts of antigens that trigger immune responses.

  • Natural antigens can activate multiple lymphocyte populations.

  • Large, simple molecules have low immunogenicity.

  • Almost any protein is recognized by antibodies.

Antibody Structure

• Antibody regions include recognition sites for specific antigens.

Antibodies and Allergies

• Normal immunoglobulin levels:

  • High IgM, IgG; low IgE.

• Allergic Reactions: High levels of IgE associated with allergies.

  • Sequence from B cell activation to plasma cells producing IgE leading to allergic responses.

Major Histocompatibility Complex (MHC)

• MHC Role: Essential for T cell education and immune function.

  • Presents foreign proteins on cell surfaces to be recognized by T cells.

  • Mutations can cause T cells to attack the body’s cells.

• MHC Proteins: Self-antigens crucial for distinguishing self from nonself.

  • Unique to the individual, important for organ transplant compatibility.

Types of Cells in Adaptive Immunity

1. B Lymphocytes (B Cells): Humoral immunity, produce antibodies upon activation.

2. T Lymphocytes (T Cells): Cell-mediated immunity.

3. Antigen Presenting Cells (APCs):

   • Essential for presenting antigens to T cells.

   • Include dendritic cells and macrophages.

T Cell Development and Education

• T Cell Education: Occurs in the thymus; involves negative and positive selection.

  • Positive selection ensures T cells recognize self-MHC.

  • Negative selection eliminates self-reactive T cells.

Naive Lymphocytes

• Naive B and T cells are immunocompetent but not yet exposed to antigens.

• Once exposed, they undergo clonal selection and activation.

Clonal Selection and Activation

• Clonal Selection: Naive lymphocyte's first antigen encounter results in activation.

• Proliferation and Differentiation: Activated lymphocytes become effector cells or memory cells.

  • Memory cells circulate to respond more quickly upon re-exposure.

Antigen-Presenting Cells (APCs)

• APCs engulf antigens and present fragments to T cells for recognition.

  • Major types include dendritic cells, macrophages, and B cells.

Cell-Mediated Immune Response

• Differentiation into CD4+ (helper) and CD8+ (cytotoxic) T cells.

  • Helper T cells activate B cells, T cells, and macrophages.

  • Cytotoxic T cells kill infected cells, foreign cells, and tumor cells.

Activation of CD8+ T Cells

• Requires APC presentation and assistance from helper T cells.

• Cytotoxic Mechanisms:

  1. Release of perforins to create pores in target cell membranes.

  2. Induction of apoptosis in infected or abnormal cells.

Vaccination and Immune Memory

• Vaccines activate adaptive immune responses and create memory T and B cells.

  • Can contain dead, living, or engineered viruses for immune stimulation.

  • Example: Cowpox utilized by Edward Jenner for smallpox vaccination.

Influenza Overview

• High incidence of severe cases each year, requires annual vaccine updates based on viral mutations.

COVID-19 Vaccination

• mRNA technology used to induce immune response and memory formation.

• Concerns regarding adjuvants enhancing immune responsiveness.