Immunology

• Why is phagocytosis important for the immune system?


  Phagocytosis is crucial for protecting the body from harmful invaders and clearing dead or damaged cells.
• What are phagocytes?


  Phagocytes are specialized cells that perform phagocytosis, such as neutrophils and macrophages.
• What are the key points of phagocytosis?


  • Performed by specialized cells called phagocytes (e.g., neutrophils, macrophages)
  • Involves engulfing particles or microorganisms
  • Part of the body's innate immune response
  • Helps in clearing dead or damaged cells
• What are the key steps in complete phagocytosis?


  1. Recognition: The phagocyte identifies the target particle
  2. Attachment: The phagocyte binds to the particle
  3. Engulfment: The cell membrane surrounds and internalizes the particle, forming a phagosome
  4. Fusion: The phagosome fuses with a lysosome, forming a phagolysosome
  5. Digestion: Lysosomal enzymes break down the engulfed particle
  6. Elimination: Waste products are expelled from the cell
• What are the key points about incomplete phagocytosis?


  • The phagocyte may partially engulf the target but fail to internalize it completely
  • The phagosome may not fully fuse with lysosomes
  • Digestion of the engulfed particle may be incomplete
  • Some pathogens have evolved mechanisms to resist complete phagocytosis
• Which pathogen is known to prevent phagosome-lysosome fusion?


  Mycobacterium tuberculosis can prevent phagosome-lysosome fusion.
• What is the complement system a part of?


  The innate immune system
• What is the primary function of the complement system?


  To enhance the ability of antibodies and phagocytes to clear pathogens
• What are the key components of the complement system?


  • Over 30 proteins
  • C1-C9 complement proteins
  • Factor B, D, and P (properdin)
  • Mannose-binding lectin (MBL)
  • Regulatory proteins (e.g., C1 inhibitor, factor H, factor I)
• How are the proteins of the complement system activated?


  They are typically inactive in the bloodstream until triggered by pathogens or other stimuli.
• What are the key steps in the classical activation pathway?

  1. C1 complex binds to antibody-antigen complexes
  2. C1 activates C4 and C2
  3. C4b2a complex forms (C3 convertase)
  4. C3 is cleaved into C3a and C3b
  5. C5 convertase forms (C4b2a3b)
  6. C5-C9 form the Membrane Attack Complex (MAC)
• What is a unique feature of the alternative activation pathway?


  It is constantly active at a low level due to spontaneous C3 hydrolysis.
• What is the role of the Membrane Attack Complex (MAC)?


  It can directly lyse some pathogens.
• What are the key steps in the alternative activation pathway?

  1. Spontaneous hydrolysis of C3 to C3(H2O)
  2. Factor B binds to C3(H2O) and is cleaved by Factor D
  3. C3 convertase (C3bBb) forms
  4. Properdin (Factor P) stabilizes C3 convertase
  5. More C3b is generated, leading to amplification
  6. C5 convertase forms, leading to MAC formation
• What initiates the lectin activation pathway?


  Binding of mannose-binding lectin (MBL) to carbohydrate patterns on pathogens
• What are the key steps in the lectin activation pathway?


  1. MBL binds to mannose residues on pathogens
  2. MBL-associated serine proteases (MASPs) are activated
  3. MASPs cleave C4 and C2
  4. C3 convertase (C4b2a) forms
  5. C3 is cleaved, leading to C5 convertase formation
  6. MAC formation proceeds
• What are the biological effects of the complement system?


  1. Opsonization of pathogens
  2. Induction of inflammation
  3. Direct lysis of some pathogens
  4. Immune complex clearance
  5. Activation of B and T cells
  6. Viral neutralization
• Which of the following is a biological effect of the complement system?


  Opsonization of pathogens
• Which types of cells are included in immunocompetent cells?


  B and T lymphocytes
• What is the role of immunocompetent cells in the immune system?


  They recognize, respond to, and remember specific antigens
• What type of white blood cells are NK cells classified as?


  Lymphocytes
• What are the key characteristics of NK cells?


  • Rapid response to threats
  • No antigen-specific receptors
  • Cytotoxic ability to kill target cells
  • Produce cytokines like IFN-γ
  • Larger than typical lymphocytes with cytotoxic granules
  • Express CD56 surface marker
• What is the "missing self" hypothesis in NK cell function?

  It refers to NK cells recognizing the absence of MHC class I molecules on target cells.
• What are the mechanisms NK cells use to kill target cells?


  1. Perforin-granzyme pathway
  2. Death receptor pathway (Fas ligand)
  3. Antibody-dependent cell-mediated cytotoxicity (ADCC)
  4. Cytokine release (e.g., IFN-γ, TNF-α)
• What role do NK cells play in pregnancy?


  Specialized uterine NK cells assist in placental development.