Innate Immunity 3/25/14 12:05 PM
• Exotoxin release- Vibrio cholerae
• Endotoxin release- Y. pestis
• Direct cytopathic effect.- influenza virus
Site of infection
• Extracellular- interstitial spaces, blood, lymph, epithelial surfaces
• Intracellular- cytoplasmic
Complement System- marks the bacteria; recognition system.
• System of proteins made in the liver, present in blood, lymph, and
o Coats the surface of bacteria and viruses and makes them
more easy for phagocytosis.
• Three componentns
o C3 most important protein
§ Main goal- opsonization- process of enabling
§ Tags bacteria for destruction
ú High energy thioester bond to stick to the
• Three pathways
o Alternative pathway- first one to act on a pathogen.
§ iC3àiC3Bb complexàC3a and C3b
§ C3 convertase- cleaves and inactivates C3.
§ Once C3b is attachedàanother Bb
attachesàcontinuously cleavesà continues coating
§ Positive feedback for amplification of coating.
§ Alternative C% convertase (C3b2bcBb)
o Lectin pathway- second way to act – binds carbs. on
o Classical pathway- Last to way- uses antibody to find
o They all cleave C3 to C3b to expose the thioester bond. • Complement Control proteins
o 2 categories
§ Plasma control proteins
ú Properdin (activator) stabilizes C3bBb complex
• Factor P
ú Factor H and Factor I (inhibit) together decrease
§ Human Cell, membrane control proteins
ú Decay- accelerating factor (DAF) leads to Bb
dissociation and inactivation
ú Membrane co-factor (MCP) enhances cleave by
factor I (Acts like Factor H)
• Enhance Phagocytosis
o Coats pathogen with Cb3 and macrophages have receptors
§ Macrophages express complement receptor 1 (CR1)-
arrays of Cr1 will recognize arrays of C3b
Preventing attacks on human Cells
• CD59 prevents recruitment of C9 to form pores. 3/25/14 12:05 PM
Innate Immune Receptor: recognize biochemical differences between animal
cells and microorganisms.
• Present on many immune cells
• Binds to diverse microbial ligands
o Lectins- binds proteins and carbohydrates.
§ Ex. Mannose receptor, glucan receptor.
o Scavenger receptor- bind charged ligands (ex nucleic acid)
o Complement receptor 3 and CR4
• Can function as
o Initiate receptor-mediated endocytosis.
o Initiate immune signaling (eg. Cytokine production).
Toll-like Receptors (TLRs)
• Response to difference sets of pathogens and drive changes in gene