University of Mary Hardin-Baylor 3

Immune System Overview

  • The immune system consists of various cells, organs, and processes that protect the body from pathogens.

    • Stem Cells: Stem cells in the bone marrow differentiate into various immune cells, including B cells and natural killer cells.

    • T Cells: Produced in the thymus, T cells are crucial for adaptive immunity.

Immune Organs and Their Functions

  • Bone Marrow:

    • Generates B cells and natural killer cells.

  • Thymus:

    • Site for T cell maturation.

    • Largest during childhood but decreases in size with age.

  • Peyer's Patches:

    • Lymphoid tissues in the duodenum, acting like tonsils to protect the gastrointestinal tract from pathogens.

  • Appendix:

    • An outpocketing of the large intestine that supports immune function but can be removed without immediate health risks.

  • Spleen:

    • Acts as a graveyard for red blood cells, storing iron.

    • Composed of red pulp (containing red blood cells) and white pulp (lymphatic tissue).

Lymphatic System

  • Lymph Nodes:

    • Receive lymph fluid via afferent vessels and send it out through efferent vessels.

    • Slows lymph flow to allow for immune cell action.

    • Critical for filtering pathogens and coordinating immune response.

Types of Immunity

  • Innate Immunity:

    • Present at birth; includes natural barriers like skin and mucus membranes.

    • Non-specific defense against pathogens.

  • Adaptive Immunity:

    • Develops over time through exposure to pathogens and vaccines.

    • Specific responses tailored to distinct pathogens.

    • Involves B cells and T cells; includes production of memory cells for faster responses on re-exposure.

B Cells and T Cells

  • B Cells:

    • Produce antibodies that tag pathogens for destruction by other immune cells.

  • T Cells:

    • Cytotoxic T Cells: Destroy infected cells directly.

    • Helper T Cells: Assist in activating B cells and other immune functions.

    • Memory T Cells: Retain information about past infections for rapid response.

Immune Response Activation

  • MHC Proteins:

    • Major Histocompatibility Complex (MHC) presents antigens.

    • MHC I: Found on nearly all cells; presents to CD8+ T cells.

    • MHC II: Found on antigen-presenting cells; presents to CD4+ T cells.

  • Activation of Immune Cells:

    • Binding of T cell receptors to MHC-antigen complexes stimulates T cell proliferation and activity.

Immune Defenses

  • Natural Killer Cells:

    • Attack and destroy foreign or infected cells using perforins to create pores in their membranes.

  • Phagocytes (Macrophages):

    • Non-specific immune cells that engulf pathogens and present their antigens to T cells.

  • Complement System:

    • A series of proteins that enhance immune responses by marking pathogens for destruction.

Inflammation and Fever

  • Inflammation:

    • Localized response to injury or infection that increases blood flow to the area, bringing immune cells to fight pathogens.

  • Fever:

    • Elevated body temperature aims to inhibit pathogen growth and enhance immune cell function but can be harmful if too high.

Antibodies and Their Functions

  • Antibody Structure:

    • Y-shaped molecules with variable segments that bind specifically to antigens.

  • Types of Antibodies:

    • IgG: Most abundant, critical for long-term immunity.

    • IgM: First antibody produced in response to an infection.

    • IgE: Involved in allergic reactions.

    • IgA: Found in mucosal areas and secretions, providing localized protection.

Immune Memory

  • Primary Immune Response:

    • The initial response to a pathogen; slower and less robust.

  • Secondary Immune Response:

    • Faster and stronger response upon re-exposure due to memory cells.

    • Encouraged through vaccinations and natural infections.