🤾🏻♂️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.
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
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