Immunity and Immune Response

Immunity Overview

  • Immunity: The body's ability to defend itself against disease and infection.

  • Forms:

    • Innate Immunity: Present at birth, providing immediate, non-specific defense.

    • Adaptive Immunity: Acquired immunity that develops over time to target specific pathogens.

Innate Immunity

  • Characteristics:

  • Born with it, fast-response.

  • Includes physical barriers like skin and mucous membranes.

  • 1st Line of Defense:

  • Physical/Chemical Barriers:

    • Skin: Composed of closely packed, keratinized cells that shed to remove microbes.

    • Mucous Membranes: Secret mucus, use cilia to trap pathogens.

    • Tears, urine, and saliva help wash away pathogens.

  • 2nd Line of Defense:

  • Internal Defenses:

    • Antimicrobial proteins, inflammation, fever.

    • Natural Killer Cells: Attack abnormal cells, releasing perforins to cause lysis.

    • Phagocytes: Ingest microbes and debris; includes neutrophils and macrophages.

Adaptive Immunity

  • Characteristics:

  • Develops after exposure to antigens (foreign substances).

  • Specificity: Recognizes specific pathogens; memory that enhances response to re-exposure.

  • Mechanism:

  • When exposed to an antigen, B cells and T cells are activated to produce specific antibodies and destroy infected cells.

  • Memorization of Antigens:

  • Primary Immune Response: Slow and weak at first; helps create memory cells for faster secondary responses.

  • Secondary Immune Response: Quicker, stronger attack due to memory cells.

Cells of the Immune System

  • B Cells: Produce antibodies; differentiate into memory and plasma cells.

  • T Cells:

  • Helper T Cells: Enhance immune responses by releasing cytokines.

  • Cytotoxic T Cells: Directly kill infected cells.

  • Memory T Cells: Rapidly respond to previously encountered antigens.

Activation of Lymphocytes

  • B-cell Activation:

  • B cell receptors bind to antigens; help from Helper T cells enhances response.

  • Rapid division forms plasma cells that produce antibodies.

  • T-cell Activation:

  • Recognize antigens presented by Major Histocompatibility Complex (MHC).

  • Requires costimulation to prevent accidental activation.

Antigens

  • Definition: Substances triggering an immune response, potentially immunogenic.

  • Can be complete (fully immunogenic) or incomplete antigens (haptens).

  • Foreign Antigens: Introduced into the body through pathogens; self-signature is not recognized.

  • Self Antigens: Produced by the body; can provoke an immune response if associated with disease or damage.

Complement System & Cytokines

  • Complement System:

  • Group of proteins that enhance phagocytosis, cause cytolysis of pathogens, and increase inflammation.

  • Cytokines:

  • Hormones regulating immune responses, aiding the growth and differentiation of cells involved in immunity.

Effects of Aging on Immunity

  • Decreased responsiveness to infections and vaccines.

  • Increased production of autoantibodies leading to autoimmune disorders.

  • Reduced T-cell and B-cell function due to thymic atrophy.