Immunity and Immune Response

Immune System Overview

Eyes

  • Washing and antibiotic activity of tears.

Lymph Nodes

  • Phagocytosis by Macrophages: Involved in engulfing and digesting pathogens.

  • Natural Killer (NK) Cells: Attack and destroy abnormal body cells (e.g., virus-infected or cancer cells).

Skin

  • Physical Barrier: Acts as a frontline defense against pathogens.

Respiratory Tract

  • Entrapment: Mucus traps pathogens, which are then transported to the throat via ciliary motion.

  • Phagocytosis by Macrophages: Protects the lungs.

  • Response Mechanisms: Sneezing and coughing help eliminate entry of pathogens.

Blood

  • Phagocytosis: Engaged by macrophages and granulocytes to eliminate pathogens.

  • Digestion: Utilizes enzymes to break down invaders.

  • Complement Proteins: Attack pathogens as part of immune response.

Bone Marrow

  • Phagocytosis: Involvement of macrophages and granulocytes.

  • NK Cells: Act against abnormal body cells.

Liver

  • Kupffer Cells: Macrophages in the liver performing phagocytosis.

Spleen

  • Phagocytosis by Macrophages: Filters blood and removes pathogens.

  • NK Cells: Active in targeting and destroying infected cells.

Digestive System

  • Destruction: Gastric acid, bile, and enzymes destroy pathogens.

  • Elimination: Vomiting and diarrhea expel intruders.

Urogenital Tract

  • Flushing Mechanism: Urine's acidity combats pathogens and flushes them away.

Levels of Immunity

Innate Immunity

  • Rapid Responses: First line of defense against a broad range of microbes.

Acquired Immunity

  • Slower Responses: Tailored to specific pathogens, requiring exposure to develop.

  • Components: Humoral and cell-mediated responses involving antibody production and cytotoxic lymphocyte function.

Second Line of Defense: Nonspecific Responses

Phagocytosis

  • Process: White blood cells engulf and destroy foreign materials.

  • Cell Types: Neutrophils and macrophages are primary phagocytes.

Natural Killer (NK) Cells

  • Cell Type: Lymphocytes found in various tissues (lymph nodes, spleen, etc.).

  • Function: Recognize and kill infected or cancerous cells by triggering apoptosis.

Inflammation

  • Mechanism: Warmth, redness, swelling, and pain occur in response to injury.

  • Cell Involvement: Histamine release triggers leukocyte movement to sites of injury, leading to pus formation and lymph node enlargement.

Fever

  • Effect of Phagocytes: Release substances that raise body temperature, stimulating immune functions and impeding pathogen replication.

Interferon

  • Function: Substances preventing virus production in nearby cells.

  • Types: IFNα (alpha), IFNβ (beta), and IFNγ (gamma), each stimulating immune responses.

Complement

  • Function: Specialized proteins enhancing immune responses by coating, destroying foreign cells, and promoting inflammation.

  • Mechanism: Attracts phagocytes for enhanced pathogen removal.

Specific (Acquired) Immunity

Characterization

  • Specific Response: Targeted towards specific pathogens, acquired throughout life.

  • Stimulation: By antigens that induce lymphocyte activity.

Antigens

  • Definition: Foreign substances that provoke immune responses, activating T cells and B cells.

T Cells

  • Different Types:

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

    • Cytotoxic T Cells: Destroy infected body cells.

    • Regulatory T Cells: Modulate immune response to prevent overactivity.

B Cells

  • Function: Produce antibodies (immunoglobulins) that bind to pathogens, marking them for destruction.

  • Types of Antibodies:

    • IgM: First response at infection site.

    • IgG: Most abundant, found in blood and tissues.

    • IgA: Present in secretions such as tears, saliva, and mucus.

Antibody Functionality

  • Mechanisms:

    • Binding antigens to promote phagocytosis.

    • Neutralizing toxins and activating NK cells.

    • Activating complement systems for enhanced pathogen destruction.

Immune Memory

  • Long-Term Response: Antibodies persist allowing rapid and robust reaction on re-exposure to pathogens, even lasting for years or a lifetime.

Cytokines

  • Role: Regulatory proteins influencing immune system processes.

  • Interleukins: Key cytokines that mediate various immune responses, enhancing functions of immune cells (e.g., IL-1 promotes inflammation).

Summary of Key Cytokines and Their Effects

  • IL-1: Mediates inflammation.

  • TNF-α: Involved in inflammation and cell death.

  • IFN-α and IFN-β: Induce antiviral states in cells and support immune activation.

  • Interleukin 2 (IL-2): Promotes T cell proliferation; key for adaptive immunity.

  • Interleukin 4 (IL-4): Activates B cells and promotes antibody responses.

Note: Cytokines are crucial for both innate and adaptive immune responses, impacting a variety of immune functions and interactions. They play multiple roles often expressed by different cell types in the immune system.