3: Complement + Interferon

Complement System

Activated in cascade, 3 pathways, non-specific

Classical Pathway:

triggered by Antigen-Antibody Complexes (IgG, IgM)

Alternative Pathway

triggered by pathogen surfaces (polysaccharides)

Lecthin Pathway

triggered by mannose-binding lectin on microbes

The complement system is key to combat enteric gram ___ bacteria

negative

Function of Complement

1. Cytolysis

2. Inflammation

3. Opsonization

Cytolysis:

Begins formation of membrane attack complex (MAC: C5-C9)

Creates pores in pathogen membrane → cell death

Inflammation:

C3a + C5a → stimulate mast cells, increase vascular permeability

C5a → chemotactic factor that recruits phagocytes to infection site

Opsonization:

C3b → binds pathogen; opsonin

Enhances phagocytosis by macrophages → makes microbes easier to destroy

Inactivation of the complement

by Plasmin, needed to avoid damage to host cells

Some people with plasmin deficiencies have susceptibility to infections and/or hypersensitivities

Type 1 Interferons

Infected cells release IFN → binds → induces antiviral proteins (AVPs)

1. AVPS

2. IFN-a

3. IFN-b

AVPs:

block viral protein synthesis and degrades viral nucleic acids → prevents viral replication in neighboring cells

IFN-a:

Produced by infected leukocytes

Inhibits viral replication, degrades viral RNA

IFN-B:

Produced by fibroblasts and other infected cells

Strong antiviral, regulates inflammation

Type 2 Interferons

IFN-y

IFN-y:

Produced by T and NK cells

Immune system regulation and links two systems