Innate immune system

Introduction to Immunology

  • Immunology Definition: Study of the body's defense mechanisms against diseases, derived from Latin "immunis" meaning free or exempt from disease.

  • Importance of Understanding: Acknowledging the body’s defenses is crucial before addressing how diseases disrupt homeostasis.

Defense Mechanisms of the Body

  • Constant Exposure to Pathogens: The human body encounters various microscopic organisms such as bacteria, viruses, fungi, and potential infectious agents regularly.

  • Commensal Organisms: Not all organisms attacking; some coexist without harm but can become harmful if the body is compromised.

Key Organs of the Immune System

  • Lymphatic System: Vital for immune function, includes:

    • Lymph Nodes & Tonsils: Part of modified lymphatic system.

    • Spleen: Monitors aged cells (e.g., red blood cells) and helps in infection response.

    • Thymus: Responsible for T cell maturation and adaptive immune response.

  • Chronic Infection Example: Malaria can lead to spleen inflammation due to the high load of infected blood.

Immune System Control and Energy Use

  • Immune responses require significant energy and must be tightly regulated.

  • Self vs. Non-Self Identification: The immune system distinguishes between the body's own cells and foreign antigens to prevent autoimmunity or unnecessary activation.

Types of Pathogens

  • Viruses, Bacteria, Fungi: Common pathogens with varying treatment complexities (e.g., antifungals are challenging since fungi are eukaryotic).

  • Protozoa & Toxins: Can also induce diseases and affect body functions, prompting hypersensitivity or allergic responses.

Severe Combined Immunodeficiency Syndrome (SCID)

  • Definition: A rare condition where individuals lack a functional immune system.

  • Case Study: David Philip Vedder, known as the "boy in the bubble," lived in isolation due to SCID and faced significant risks from infections.

  • Bone Marrow Transplant Attempt: Attempted transplant from a sister led to complications due to unexpected exposure to Epstein-Barr virus (EBV).

Infectious Agents and Immune Response

  • First Line of Defense: Skin acts as a barrier; saliva, gastric acidity, and other secretions assist in preventing infections.

  • Inflammatory Response: Initiated upon infection, causing redness, heat, swelling due to increased blood flow and white cell recruitment.

Non-Specific Defenses

  • Primary Defense Mechanisms: Include skin and bodily secretions that inhibit pathogen entry.

  • Secondary Defense Mechanisms: Activated immune cells and proteins like cytokines that help signal and mobilize the immune response, including fever (pyrexia).

Types of Immune Responses

  • Innate vs. Adaptive Immunity: Innate is the body’s first line of defense causing rapid, general responses; adaptive provides long-term, specific immunity via B cells and T cells.

  • Phagocytes: Engulf and digest pathogens, presenting their antigens to T cells to activate the specific immune response.

Cytokines and Their Role

  • Definition: Small proteins released by immune cells to modulate the immune response, causing fever and activating nearby cells.

  • Types: Include interleukins, which can signal to other leukocytes and raise body temperature for pathogen control.

Complement System

  • Function: A group of proteins constituting part of the innate immune response that can lead to lysis (bursting) of pathogens through various pathways.

  • Pathways: Include classical (antibody-mediated), lectin, and alternative pathways all leading to pore formation in bacterial cells, facilitating their destruction.

Phagocytic Cells

  • Types: Include macrophages, neutrophils, and natural killer cells, all of which work to identify and eliminate pathogens through processes like phagocytosis and apoptosis.

  • Natural Killer Cells: Specialized in targeting virally infected and cancer cells by recognizing abnormal cell markers.

Summary of the Immune System's Function

  • Identifying Self vs. Non-Self: Immune cells use MHC (major histocompatibility complex) receptors for identification.

  • Response to Cancer: The immune system can recognize and target cancerous cells, demonstrating its role in maintaining cellular integrity.

Conclusion

  • Understanding the multi-layered defense mechanisms of the immune system is essential for comprehending how diseases disrupt homeostasis and the significance of immunological research.