Human Physiology Engineering

🤾🏻‍♂️Human Physiology Engineering Unit 12 – Immune System

The immune system is a complex network of cells, tissues, and organs that defend the body against harmful agents. It comprises innate and adaptive components, working together to provide immediate and long-lasting protection. Understanding its key elements and processes is crucial for grasping how our bodies fight disease. Immunity can be passive or active, acquired naturally or artificially. The immune response involves antigen recognition, cellular activation, and memory formation. Disorders like immunodeficiencies and autoimmune diseases highlight the importance of a balanced immune system. Engineering applications in immunology are advancing medical treatments and diagnostics.

Key Components of the Immune System

  • Consists of a complex network of cells, tissues, and organs that work together to defend the body against infectious agents and other harmful substances
  • Lymphoid organs include the thymus, spleen, lymph nodes, and bone marrow which produce, mature, and store immune cells
  • Innate immune system provides immediate, non-specific defense against pathogens through physical and chemical barriers, inflammation, and phagocytosis
    • Includes skin, mucous membranes, and various immune cells (neutrophils, macrophages, and natural killer cells)
  • Adaptive immune system develops specific, long-lasting immunity to particular pathogens through the action of lymphocytes (T cells and B cells)
    • Involves antigen recognition, clonal expansion, and memory cell formation
  • Cytokines are signaling molecules that regulate and coordinate immune responses by facilitating communication between immune cells
  • Complement system enhances the ability of antibodies and phagocytic cells to clear pathogens and damaged cells from the body

Types of Immunity

  • Passive immunity provides temporary protection through the transfer of antibodies from another source
    • Naturally acquired passive immunity occurs when maternal antibodies are transferred to the fetus through the placenta or to the infant through breast milk
    • Artificially acquired passive immunity involves the administration of preformed antibodies (immunoglobulins) through medical interventions
  • Active immunity develops when an individual's immune system produces antibodies in response to an antigen
  • Naturally acquired active immunity results from exposure to a pathogen through infection, leading to the development of long-lasting immunity
  • Artificially acquired active immunity is induced by vaccines, which contain weakened, killed, or fragmented pathogens or their toxins
    • Vaccines stimulate the immune system to produce antibodies without causing the disease itself
  • Herd immunity occurs when a significant portion of a population becomes immune to an infectious disease, reducing the likelihood of its spread

Immune Response Process

  • Antigen recognition is the first step, where immune cells identify foreign substances (antigens) through specific receptors
  • Innate immune response is triggered immediately upon antigen detection, involving inflammation, phagocytosis, and the release of antimicrobial compounds
    • Macrophages and dendritic cells engulf and destroy pathogens while presenting antigens to T cells
  • Adaptive immune response is activated when innate immunity is insufficient, leading to the proliferation and differentiation of antigen-specific lymphocytes
    • T cells mature into cytotoxic T cells that directly kill infected cells or helper T cells that regulate the immune response
    • B cells mature into plasma cells that secrete antibodies specific to the encountered antigen
  • Clonal expansion occurs when activated lymphocytes rapidly divide and multiply to create a large pool of antigen-specific cells
  • Memory cell formation follows the primary immune response, where a subset of activated lymphocytes becomes long-lived memory cells
    • Memory cells enable a faster and stronger secondary immune response upon subsequent encounters with the same antigen

Cellular and Molecular Mechanisms

  • Antigen presentation involves the processing and display of antigenic peptides on the surface of antigen-presenting cells (APCs) via major histocompatibility complex (MHC) molecules
    • MHC class I molecules present intracellular antigens to cytotoxic T cells, while MHC class II molecules present extracellular antigens to helper T cells
  • T cell activation requires both antigen recognition through the T cell receptor (TCR) and co-stimulatory signals provided by APCs
    • CD4+ helper T cells secrete cytokines to regulate the immune response, while CD8+ cytotoxic T cells directly kill infected or abnormal cells
  • B cell activation occurs when B cells encounter their specific antigen and receive signals from helper T cells
    • Activated B cells differentiate into plasma cells that secrete large quantities of antibodies
  • Antibodies neutralize pathogens, opsonize them for phagocytosis, and activate the complement system
    • There are five classes of antibodies (IgM, IgG, IgA, IgE, and IgD) with different functions and locations in the body
  • Cytokine signaling orchestrates the immune response by regulating cell proliferation, differentiation, and effector functions
    • Pro-inflammatory cytokines (IL-1, IL-6, TNF-α) promote inflammation, while anti-inflammatory cytokines (IL-10, TGF-β) suppress immune responses

Disorders and Diseases of the Immune System

  • Immunodeficiencies are disorders characterized by a weakened immune system, increasing susceptibility to infections
    • Primary immunodeficiencies are genetic disorders (severe combined immunodeficiency, X-linked agammaglobulinemia)
    • Secondary immunodeficiencies are acquired due to factors like malnutrition, certain medications, or HIV/AIDS
  • Autoimmune diseases occur when the immune system mistakenly attacks the body's own tissues
    • Examples include rheumatoid arthritis, systemic lupus erythematosus, and multiple sclerosis
  • Allergies are hypersensitivity reactions to normally harmless substances (allergens) mediated by IgE antibodies
    • Symptoms range from mild (hay fever) to severe (anaphylaxis)
  • Graft rejection occurs when the immune system recognizes transplanted tissue as foreign and mounts an immune response against it
    • Immunosuppressive drugs are used to prevent rejection in organ transplant recipients
  • Cancer immunology explores the complex interactions between the immune system and tumor cells
    • Immunotherapies harness the immune system to fight cancer by enhancing its ability to recognize and destroy tumor cells

Engineering Applications in Immunology

  • Vaccine development utilizes genetic engineering and recombinant DNA technology to create safer and more effective vaccines
    • Subunit vaccines contain purified antigens, while DNA vaccines deliver genes encoding antigenic proteins
  • Monoclonal antibodies are engineered antibodies produced by identical immune cells, used for targeted therapies and diagnostics
    • Applications include cancer treatment (checkpoint inhibitors), autoimmune disorders (TNF-α inhibitors), and infectious diseases (antiviral antibodies)
  • Immunoassays are diagnostic tools that detect the presence of specific antigens or antibodies in a sample
    • Enzyme-linked immunosorbent assay (ELISA) and lateral flow assays (rapid tests) are commonly used
  • Biopharmaceuticals are drugs produced using living organisms, often involving the manipulation of immune system components
    • Examples include recombinant cytokines (interferon, interleukin-2) and fusion proteins (etanercept)
  • Immunoengineering focuses on the design and manipulation of immune cells and molecules for therapeutic purposes
    • Chimeric antigen receptor (CAR) T cell therapy genetically modifies a patient's T cells to target and destroy cancer cells

Cutting-Edge Research and Future Directions

  • Immunoinformatics applies computational methods to analyze and predict immune system functions and interactions
    • Involves the development of databases, algorithms, and models to study immunological data
  • Systems immunology takes a holistic approach to understanding the immune system by integrating data from various levels (genes, proteins, cells, tissues)
    • Aims to unravel the complex networks and feedback loops that regulate immune responses
  • Microbiome research investigates the role of the human microbiome in shaping immune system development and function
    • Dysbiosis (imbalance in the microbiome) has been linked to various immune-related disorders
  • Personalized immunotherapy tailors treatments to an individual's unique immune profile and disease characteristics
    • Involves the use of biomarkers, genetic profiling, and patient-specific immune cell engineering
  • Regenerative immunology explores the use of immune cells and molecules to promote tissue repair and regeneration
    • Macrophages and regulatory T cells have shown potential in enhancing wound healing and reducing fibrosis

Practical Implications and Case Studies

  • Vaccine hesitancy and misinformation have hindered the success of immunization programs, as seen in the resurgence of measles outbreaks
    • Effective communication and public education are crucial to promote vaccine uptake
  • The COVID-19 pandemic has highlighted the importance of rapid vaccine development and the role of the immune system in disease progression
    • mRNA vaccines (Pfizer-BioNTech, Moderna) and viral vector vaccines (AstraZeneca, Johnson & Johnson) were developed in record time
  • Immunotherapies have revolutionized cancer treatment, with notable successes in melanoma and lung cancer
    • Ipilimumab (CTLA-4 inhibitor) and nivolumab (PD-1 inhibitor) have significantly improved survival rates in advanced melanoma patients
  • Autoimmune diseases like rheumatoid arthritis and inflammatory bowel disease have benefited from targeted therapies that modulate the immune response
    • TNF-α inhibitors (infliximab, adalimumab) have been effective in reducing inflammation and improving quality of life
  • The development of rapid diagnostic tests for infectious diseases, such as HIV and influenza, has enabled earlier detection and treatment
    • Point-of-care testing using lateral flow assays has increased access to diagnostics in resource-limited settings


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© 2024 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.