6- Cell function and PRRs

• Direct PAMP recognition


  PRR directly binds to PAMP
• Indirect PAMP recognition


  Receptor binds to an intermediate opsonin which binds to the pathogen
• Opsonin


  Makes things easier to digest, like a "dos meds in peanut butt"
• PRR

  • Germ line encoded
  • Binds the same target every time
  • Affinity never increases (have multiple different families with different targets)
• PRR families

  • Toll-like (TLR)
  • C-type Lectin Receptors (CLRs)
  • RIG-I-like Receptors (RLR)
  • NOD-like
• Toll-like Receptors (TLRs)

  • Have extracellular Leucine rich repeats that bind to PAMPs and DAMPs
  • Hook-like structure
  • Found on surface, endosome, lysosome
  • Form dimers (usually homodimers)
  • Bind to PAMPs to activate signaling pathway
• Adapter proteins

  Mediate signaling pathways like NF-kB, IRF, AP-1
• 1. type Lectin Receptors (CLRs)


  • On surface of APCs
  • Recognize components in cell wall (sugar, polysaccharides)
  • Signaling pathways: NF-kB, AP-1
  • Induce production of cytokines, microbials
  • Threshold effect for activation
• RIG-I-like Receptors (RLRs)

  • React as helicases and respond to double stranded RNAs
  • Function in the cytosol
  • Signaling pathways: NF-kB, IRF, AP-1
• NOD-like Receptors

  • Cytosolic
  • Contain Leucine rich repeats like TLRs
  • Activated by intracellular PAMPs
  • Recognize parts of bacterial cell wall
  • Signaling: AP-1, NF-kB
• Opsonins


  • Surfactant collectin proteins
  • Antibodies
  • Mannose Binding Lectin
  • Ficolins
  • C-reactive protein
• Opsonin function

  Bind to PAMP then to CD91 receptor, causing phagocytosis
• Mannose Binding Lectin is found in blood and respiratory tract, binds carbohydrates
• Ficolins are found in blood, bind acetylated sugars, interact with CD91
• 1. reactive protein binds to bacteria, fungi, parasites, and is bound by Fc receptors