🔬General Biology I Unit 42 – The Immune System

What's the Immune System?

• Complex network of cells, tissues, and organs that work together to defend the body against infectious agents and other harmful substances
• Protects the body from pathogens (bacteria, viruses, fungi, parasites) and other foreign invaders
• Involves two main types of immunity: innate immunity and adaptive immunity
  • Innate immunity provides immediate, non-specific defense
  • Adaptive immunity develops over time and is highly specific to particular pathogens
• Helps to identify and eliminate abnormal or damaged cells, such as cancer cells
• Plays a crucial role in maintaining overall health and well-being
• Constantly vigilant, working 24/7 to keep the body safe from harm
• Can distinguish between "self" and "non-self" substances to avoid attacking the body's own cells

Key Players: Cells and Organs

• White blood cells (leukocytes) are the primary cells involved in the immune response
  • Neutrophils: engulf and destroy bacteria and fungi
  • Monocytes: develop into macrophages that consume pathogens and debris
  • Lymphocytes: T cells and B cells that are crucial for adaptive immunity
• Lymphoid organs are where immune cells develop, mature, and interact
  • Bone marrow: produces all blood cells, including immune cells
  • Thymus: site of T cell maturation
  • Spleen: filters blood and stores platelets and white blood cells
  • Lymph nodes: trap pathogens and facilitate interactions between immune cells
• Skin and mucous membranes (respiratory, digestive, and urogenital tracts) serve as physical and chemical barriers to pathogens
• Complement system consists of proteins that enhance the immune response by promoting inflammation and destroying pathogens
• Cytokines are signaling molecules that help regulate and coordinate the immune response

Innate Immunity: The First Line of Defense

• Innate immunity is the body's first response to a pathogen or foreign substance
• Non-specific defense mechanisms that act quickly to prevent the spread of infection
• Physical barriers include skin, mucous membranes, and secretions (saliva, tears, mucus)
  • Skin provides a tough, waterproof barrier that prevents pathogens from entering the body
  • Mucous membranes trap and remove pathogens and debris
• Chemical barriers include enzymes (lysozyme), acid (stomach), and antimicrobial peptides (defensins)
• Cellular components of innate immunity include phagocytes (neutrophils, macrophages) and natural killer cells
  • Phagocytes engulf and destroy pathogens
  • Natural killer cells recognize and kill virus-infected cells and tumor cells
• Inflammatory response is a key component of innate immunity
  • Involves increased blood flow, permeability of blood vessels, and recruitment of immune cells to the site of infection or injury
  • Helps to isolate and eliminate pathogens and promote healing

Adaptive Immunity: Your Personal Army

• Adaptive immunity is a highly specific, targeted response to a particular pathogen
• Develops more slowly than innate immunity but provides long-lasting protection
• Involves two main types of lymphocytes: T cells and B cells
  • T cells mature in the thymus and are responsible for cell-mediated immunity
    • Helper T cells stimulate B cells and other immune cells
    • Cytotoxic T cells directly kill virus-infected cells and tumor cells
  • B cells mature in the bone marrow and are responsible for humoral immunity
    • Produce antibodies that neutralize pathogens and mark them for destruction
• Antigen-presenting cells (dendritic cells, macrophages) display pathogen fragments to T cells, initiating the adaptive immune response
• Immunological memory allows for a faster, stronger response upon subsequent exposure to the same pathogen
  • Memory B cells and memory T cells persist after an infection is cleared
  • Provide rapid, efficient protection against future infections by the same pathogen

How Immune Responses Work

• Immune responses involve a complex interplay between innate and adaptive immunity
• Innate immune response is triggered by the recognition of pathogen-associated molecular patterns (PAMPs) by pattern recognition receptors (PRRs)
  • PAMPs are conserved molecular structures shared by many pathogens (bacterial cell wall components, viral nucleic acids)
  • PRRs are expressed by various immune cells and initiate signaling cascades that lead to inflammation and the activation of adaptive immunity
• Adaptive immune response begins with the activation of T cells and B cells by antigen-presenting cells
  • T cells recognize antigens presented on the surface of infected cells or antigen-presenting cells
  • B cells recognize antigens in their native form and produce antibodies specific to those antigens
• Effector functions of the adaptive immune response include:
  • Cytotoxic T cells directly killing infected cells
  • Helper T cells secreting cytokines to stimulate other immune cells
  • B cells producing antibodies that neutralize pathogens and mark them for destruction
• Immune responses are carefully regulated to prevent excessive inflammation and autoimmunity
  • Regulatory T cells help to suppress immune responses and maintain tolerance to self-antigens
  • Cytokines and other signaling molecules help to fine-tune the balance between activation and suppression of the immune system

When Things Go Wrong: Immune Disorders

• Immunodeficiencies occur when the immune system is weakened or unable to function properly
  • Primary immunodeficiencies are genetic disorders that affect the development or function of immune cells (severe combined immunodeficiency, X-linked agammaglobulinemia)
  • Secondary immunodeficiencies are acquired conditions that suppress the immune system (HIV/AIDS, malnutrition, certain medications)
• Autoimmune disorders occur when the immune system mistakenly attacks the body's own tissues
  • Examples include rheumatoid arthritis, multiple sclerosis, lupus, and type 1 diabetes
  • Often involve a combination of genetic and environmental factors
• Allergies are hypersensitivity reactions to normally harmless substances (allergens)
  • Mediated by IgE antibodies and mast cells
  • Symptoms can range from mild (hay fever) to severe (anaphylaxis)
• Chronic inflammation is associated with various diseases, including cardiovascular disease, diabetes, and cancer
  • Involves persistent activation of the immune system and the production of inflammatory mediators
  • Can contribute to tissue damage and the development of chronic conditions

Boosting Immunity: Vaccines and Lifestyle

• Vaccines are a safe and effective way to stimulate the immune system and provide protection against infectious diseases
  • Contain weakened or inactivated pathogens, or components of pathogens (antigens)
  • Induce the production of antibodies and the development of immunological memory
  • Have greatly reduced the incidence of many once-common diseases (measles, polio, diphtheria)
• Lifestyle factors can significantly impact immune function
  • Adequate sleep helps to regulate the production of immune cells and cytokines
  • Regular exercise promotes the circulation of immune cells and reduces inflammation
  • A balanced diet rich in fruits, vegetables, and whole grains provides essential nutrients for immune cell function
  • Stress management techniques (meditation, deep breathing) can help to reduce the negative impact of chronic stress on the immune system
• Certain supplements and natural products may help to support immune function
  • Vitamin C, vitamin D, and zinc play important roles in immune cell function and regulation
  • Probiotics can help to maintain a healthy gut microbiome, which is closely linked to immune function
  • Herbal remedies (echinacea, elderberry) may have immune-boosting properties, but more research is needed to confirm their effectiveness

Cool Immune System Facts

• The immune system is constantly working, even when we're not sick
  • It's estimated that the immune system eliminates around 500-1000 precancerous cells every day
• The gut is home to about 70% of the body's immune cells
  • The gut microbiome plays a crucial role in shaping the immune system and maintaining immune homeostasis
• The immune system can remember previous infections for decades
  • Immunological memory allows for a rapid, efficient response to pathogens encountered in the past
• Some immune cells can live for years or even decades
  • Memory B cells and memory T cells can persist in the body for many years after an infection is cleared
• The immune system is highly adaptable and can learn to recognize new pathogens
  • Through a process called somatic hypermutation, B cells can generate antibodies with increased affinity for a specific antigen
• The immune system and the nervous system are closely interconnected
  • Immune cells and neurons communicate through shared signaling molecules (cytokines, neurotransmitters)
  • This crosstalk helps to regulate immune responses and maintain homeostasis
• The immune system plays a role in the development of the brain
  • Immune cells and cytokines are involved in the formation of neural circuits and the pruning of synapses during brain development