Immune Defenses and Lymphatic System Quiz

Immune Defences

• External Epithelia: Skin, mucous membranes (airways, gastrointestinal tract, reproductive tract) provide the first line of defense.
• Secretions: Mucus, cilia, defensins act as additional barriers.
• Inflammation: Occurs when barriers are breached; involves activation of pattern recognition receptors, triggering release of signaling molecules like histamine, peptides, cytokines, and chemokines.
• Signs of Inflammation: Pain, heat, redness, swelling.

Lymphatic System

• Lymphatic Vessels: Transport lymph throughout the body.
• Lymph Nodes: Intersections of lymphatic vessels, acting as immune cell hubs for interaction and activation.
• Lymph: Colorless fluid containing white blood cells that circulates within the lymphatic system.
• Thymus: Organ responsible for T cell development and maturation.
• Spleen: Filters blood, removes damaged red blood cells, and stores white blood cells.

Immune Cells

• Blood: Contains red blood cells (oxygen transport) and white blood cells (immune defense).

Red Blood Cells

• Carry oxygen.
• 5-6 million per microliter of blood.
• Production rate: ~2 million per second.
• Lifespan: ~110 days.
• Transport oxygen and carbon dioxide.

White Blood Cells

• Immune cells, numerous types including: neutrophils, macrophages, monocytes, eosinophils, mast cells, basophils, T cells, B cells, and dendritic cells.
• Classified as innate or adaptive immunity.

Innate Immunity

• Initial response (within 12 hours) to danger signals and activation of immune cells.
• Limited specificity.
• Found in all tissues, especially at barrier sites.
• Rapid response following infection.
• Limited memory.

Adaptive Immunity

• Takes longer to activate (days following barrier breach).
• Highly specific to particular proteins/antigens.
• Primarily found in lymphoid organs.
• Long-lasting memory.

Key Players In Innate Immunity:

• Neutrophils: Most abundant white blood cell, active phagocytic cells, engulf and kill pathogens, employ neutrophil extracellular traps (NETs) to trap and kill pathogens, short-lived.
• Macrophages: Develop from precursors in tissues, active phagocytic cells, consume and kill pathogens, activated by inflammation, long-lived.
• Dendritic Cells: Develop from precursors in tissues, active phagocytic cells, migrate from peripheral tissues to lymph nodes, transport antigens to T cells in lymph nodes, bridge innate and adaptive immunity by activating the adaptive immune response.
• Complement: Cascade of proteins in serum (blood) that sense danger, enhances immune response, activated by antibodies or pathogen molecules, can directly kill pathogens or attract immune cells to an infection site.

Stages of Adaptive Immune Response:

• Triggered by innate immune response.
• Dendritic cells, macrophages, and neutrophils signal to adaptive immune cells.
• Innate immune cells can clear mild infections; otherwise, they alert adaptive immune cells.

1. T Cell Activation: Finding the right T and B cells.
2. T Cell Differentiation: Deciding how to respond.
3. T Cell Effector Stage: Immune response.

B Cells

• B cell receptors (BCRs) can bind to native proteins or antigens without accessory cells (processing not required).
• Up to 10^12 different BCRs.
• Produce antibodies, classified into different types:
  • IgM: Low affinity, high avidity.
  • IgG: Most abundant antibody in serum.
  • IgA: Found at mucosal sites.
  • IgE: Involved in allergy and anti-helminth worm responses.
• Antibodies are made by plasma cells (differentiated B cells).
• Antibody mechanisms:
  • Neutralize pathogens.
  • Activate complement to enhance immune response.
  • Enhance phagocytosis (opsonization) by binding to receptors on phagocytes.

T Cells

• Around 10^8 different T cell receptors (TCRs).
• T cells recognize processed antigens presented on MHC molecules on the surface of antigen-presenting cells (require accessory cells).
• CD4 T cells (Helper T cells):
  • Recognize longer peptides on MHC class II molecules, expressed by professional antigen-presenting cells (B cells, macrophages, dendritic cells).
  • Support other immune cells by:
    • Enhancing CD8 T cell responses.
    • Aiding B cells in producing high-affinity antibodies.
    • Activating macrophages for more effective pathogen destruction.
• CD8 T cells (Cytotoxic T cells):
  • Recognize shorter peptides on MHC class I molecules, expressed by all nucleated cells (B cells, macrophages, dendritic cells, epithelial cells).
  • Kill infected cells and tumor cells by releasing toxic granules.
• Memory trick: 4 x 2 = 8 (CD4 T cells with MHC class II), 8 x 1 = 8 (CD8 T cells with MHC class I).

Specificity:

• Spike Protein: Antigen found on the surface of some viruses.
• Epitope: Peptide chains, parts of an antigen recognized by immune receptors (BCRs and TCRs).

Adaptive Immune Cell Locations:

• Generation: Primary lymphoid organs (thymus and bone marrow).
• Activation: Secondary lymphoid organs (lymph nodes and spleen).

Timings of the Immune Response:

• Innate: 0-5 days (dendritic cells, neutrophils, macrophages, monocytes).
• Adaptive: 3-15 days (B cells, CD4 T cells, CD8 T cells).
• Long-lived: Months to years (long-lived plasma cells, memory B and T cells).

Immunological Memory

• Enables rapid control of previously encountered pathogens.
• Memory T and B cells provide a rapid response upon reinfection.
• Memory cells act at different locations in the body to protect the host.

Key Points

• B and T cells form the adaptive immune system.
• Specialized receptors (BCRs and TCRs) on their surfaces allow recognition of antigens.
• B cells produce pathogen-specific antibodies.
• CD4 T cells coordinate other immune cells.
• CD8 T cells kill infected cells and tumors.
• Memory T and B cells ensure rapid responses to previously encountered pathogens.

Test your knowledge on the body's immune defenses, including the role of external epithelia, secretions, and inflammation. Explore the functions of the lymphatic system, including lymph transport and immune cell interaction within lymph nodes. This quiz covers essential concepts about immune cells and their functions.