IMSE 311: Pattern Recognition Receptors & Phagocytosis

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16 Terms

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Pattern Recognition Receptors (PRRs)

Encoded by host’s genomic DNA and act as sensors for extracellular infection

  • Distinguish self from nonself by recognizing PAMPs

  • Found in cellular immunity

    • Activates phagocytes > triggers cytokine secretion > adaptive immune response

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Pathogen-associated Molecular Patterns (PAMPs)

Only found in microorganisms

  • Peptidoglycan: gram-positive bacteria

  • Lipoproteins: gram-negative bacteria

  • Zymosan: yeast

  • Flagellin: flagellated bacteria

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Toll-like Receptor (TLR)

Membrane-spanning glycoproteins that share a common structural element called leuchine-rich repeats (LRRs)

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TLR1

Recognizes:

  • Lipopeptides

Targets:

  • Mycobacteria

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TLR2

Recognizes:

  • Peptidoglycan

  • Lipoproteins

  • Zymosan

Targets:

  • Gram-positive bacteria

  • Mycobacteria

  • Yeasts

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TLR3

Recognizes:

  • Double-stranded RNA

Targets:

  • RNA viruses

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TLR4

Recognizes:

  • Lipopolysaccharide

  • Fusion proteins

  • Mannan

Targets:

  • Gram-negative bacteria

  • Respiratory syncytial virus (RSV)

  • Fungi

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TLR5

Recognizes:

  • Flagellin

Targets:

  • Flagellated bacteria

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TLR6

Recognizes:

  • Lipopeptides

  • Lipoteichoic acid

  • Zymosan

Targets:

  • Mycobacteria

  • Gram-positive bacteria

  • Yeast

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TLR7 & TLR8

Recognizes:

  • Single-stranded RNA

Targets:

  • RNA viruses

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TLR9

Recognizes:

  • Double-stranded DNA

Targets:

  • DNA viruses

  • Bacterial DNA

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TLR10

TLR that is thought to be anti-inflammatory

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Phagocytosis Process

  1. Adherence: physical contact b/n WBC and Ag, aided by opsonins

  2. Engulfment: outflowing of cytoplasm to surround microorganism

  3. Formation of phagosome

  4. Granule Contact: fusion of lysosomal granules w/ phagosome

  5. Formation of phagolysosome w/ release of lysosomal contents

  6. Digestion of microorganisms by hydrolytic enzymes

  7. Excretion: release of debris to outside of cell by exocytosis

<ol><li><p><span style="color: red;">Adherence</span>: physical contact b/n WBC and Ag, aided by opsonins</p></li><li><p><span style="color: red;">Engulfment</span>: outflowing of cytoplasm to surround microorganism</p></li><li><p><span style="color: red;">Formation of phagosome</span></p></li><li><p><span style="color: red;">Granule Contact</span>: fusion of lysosomal granules w/ phagosome</p></li><li><p><span style="color: red;">Formation of phagolysosome</span> w/ release of lysosomal contents</p></li><li><p><span style="color: red;">Digestion of microorganisms by hydrolytic enzymes</span></p></li><li><p><span style="color: red;">Excretion</span>: release of debris to outside of cell by exocytosis</p></li></ol><p></p>
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Selectins

Adhesion molecule on endothelial cells lining the blood vessels for rolling of phagocytes

  • Recruitment of phagocytes to infection site

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Integrins

Adhesion molecule on endothelial cell wall for stable attachment and migration into tissues

  • Diapedesis

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Opsonins

Serum proteins that attach to a foreign cell or pathogen and help prepare it for phagocytosis