Immune System Overview Quiz

Innate Immune System

• Largely non-specific
• First line of defense: Barriers (skin, mucous membranes)
• Second line of defense: Internal Defenses (phagocytes, natural killer cells, inflammation, antimicrobial proteins, fever)
• Responses can initiate within minutes

Adaptive Immune System

• Mounts attacks against specific foreign substances
• Collectively acts as the third line of defense
• Responses take considerably more time to develop
• Independent and cooperative action with the innate system
• Composed of:
  • Humoral Immunity (B cells)
  • Cellular Immunity (T cells)

Surface Barriers (First Line of Defense)

• Skin:
  • Keratin resists weak acids and bases
  • Contains bacterial enzymes, toxins
• Mucosa:
  • Lines cavities that open to the exterior (digestive, respiratory, urinary, reproductive)
  • Contains mucus that traps microorganisms
  • Contains enzymes (lysozyme) and acidic secretions that inhibit bacterial growth
  • Contains cilia that sweeps pathogens toward the mouth
• Acid mantle in skin, vagina and stomach inhibits bacterial growth
• Enzymes in stomach digest proteins and kill microorganisms.
• Mucin traps microorganisms in thick mucus and washing them away in thin watery mucus (e.g., saliva)
• Defensins are broad-spectrum peptides toxic to bacteria
• Sweats contain dermicidin (toxic to bacteria)

Cells & Chemicals: Second Line of Defense

• Phagocytes:
  • Cells that engulf pathogens and debris via cytoplasmic extensions
  • Professional phagocytes: neutrophils, dendritic cells, macrophages, mast cells.
  • Neutrophils are the most plentiful leukocyte.
  • Macrophages and dendritic cells derive from monocytes and patrol tissues.
  • Nonprofessional phagocytes: epithelial and endothelial cells, fibroblasts
• Natural Killer (NK) cells:
  • Kill virus-infected and cancer cells
  • Non-phagocytic: induce apoptosis (programmed cell death) and secrete chemicals to enhance inflammatory response
• Inflammatory Response:
  • A complex, beneficial process triggered by tissue injury and/or infection
  • Prevents spread of damaging agents, disposes of debris, alerts the adaptive system, sets the stage for repair
  • Signs: heat, redness, swelling, pain
• Antimicrobial Proteins: Interferons(α, β, γ), Complement proteins, Fever
  • Interferons are proteins released by virus-infected cells and certain lymphocytes.
  • Complement: A group of blood proteins that promote lysis and enhance phagocytosis
  • Fever: Increased temperature inhibits microbial reproduction

Phagocytosis: 'Cell Eating'

• Adherence to pathogen (recognition)
• Phagocyte engulfs.
• Lysosome fuse with phagocytic vesicle to create phagolysosomes.
• Lysosomal enzymes digest.
• Residual body is exocytosed.
• Respiratory burst to eliminate pathogens
• Involve mainly macrophages

Hematopoietic Cell Production

• Stem cells differentiate to produce all formed elements of the blood.
• Multipotent hematopoietic stem cell (hemocytoblast) differentiates into myeloid and lymphoid stem cells.

Antimicrobial Proteins (Innate Defenses)

• Enhance innate immune defenses by directly attacking microorganisms or hindering their ability to reproduce.
• Two types are extremely important: Interferons and the Complement System

Interferons (IFNs)

• Produced by virus-infected cells and certain lymphocytes.
• Block viral protein synthesis and degrade viral RNA.
• Protect uninfected tissue cells from viruses.
• Not virus-specific so protection against one virus can extend to other viruses.
• Two types: Type I (IFN-alpha, IFN-beta) and Type II (IFN-gamma)

Complement System

• 20+ plasma proteins that circulate in inactive states.
• Destroy pathogens by lysis, opsonization, and inflammation, assisting in both innate and adaptive defenses.
• Complement proteins are activated to produce a protein complex called Membrane Attack Complex (MAC) to create pores in the plasma membrane.

Fever

• Abnormally high body temperature.
• Systemic response to invading microorganisms.
• Release of pyrogens (fever-producing substances).
• Reset hypothalamus thermostat to higher temperature.
• Liver and spleen sequester iron and zinc to inhibit bacterial growth.
• Increased metabolic rate speeds up repair processes

Adaptive Immune Response

• Humoral Immunity (antibody-mediated):
  • B cells circulate in body fluids and produce antibodies
  • Antibodies bind to and inactivate extracellular targets
• Cellular Immunity (cell-mediated):
  • T cells defend against intracellular pathogens and abnormal cells
  • T cells recognize abnormal cells by using receptors to bind to antigens presented on MHC proteins

Antigens

• Any substance that mobilizes an immune response
• A specific feature on an antigen is called an epitope or antigenic determinant
• Can be proteins, carbohydrates, lipids, nucleic acids
• Complete antigen: has immunogenicity and reactivity
• Incomplete (hapten) antigens: reactivity only; must combine with a larger protein molecule to be immunogenic

Self-Antigens: MHC Proteins

• Major histocompatibility complex that displays peptides on the surface of cells
• MHC class I proteins present proteins from inside cells
• MHC class II proteins present pathogens from outside cells
• Immune system is educated not to attack self-antigens

Adaptive Immunity: Lymphocyte Development, Maturation & Activation

• Involves 3 cell populations: B lymphocytes, T lymphocytes, Antigen-presenting cells (APCs).
• Lymphocytes develop in bone marrow and thymus
• B cells mature in bone marrow and T cells mature in thymus
• Lymphocytes develop immunocompetence and self-tolerance during maturation.
• Encounter antigen and get activated in secondary lymphoid organs ( lymph nodes, spleen etc).
• Activated lymphocytes proliferate and differentiate (into effector cells and memory cells).
• Memory cells mount a more rapid response to subsequent exposures to the same antigen.
• Clonal selection of lymphocytes

Lymphocyte Activation and Clonal Selection

• Lymphocytes are activated when their antigen receptors bind to their specific antigen.
• This activation triggers proliferation and differentiation of the lymphocyte into effector cells and memory cells.
• Clonal selection is the process where only lymphocytes with antigen receptors that bind to the particular antigen proliferate and differentiate to combat the infection.

Test your knowledge on the innate and adaptive immune systems with this comprehensive quiz. Explore the components, functions, and defense mechanisms that protect the body from pathogens. Perfect for students studying biology or healthcare-related fields.