Immunology Chapter 2 – Innate immunity: the immediate response
to infection
Lines of defense
1. Barriers: If there is an opening the pathogen can
enter and come in contact with innate immune
response.
Found in skin, gut, lungs, eyes, nose, oral cavity
o Mechanical barrier: epithelial cells joined by
tight junctions, flow of air or fluid
o Chemical barrier: fatty acids, antimicrobial
peptides and low pH
o Microbiological barrier: normal microbiota
2. Innate immunity: phagocytosis, complement, interferon,
inflammation, fever
What plays a role?
1. Soluble molecules: the complement system
Complements are proteases proteins present in
circulation and tissues and are present in inactive form.
They consist of plasma proteins (30 different forms) with
enzymatic activity.
Alternative pathway, MBL pathway (lectin pathway),
Classical pathway complement activation
cleavage C3 into C3b and C3a:
o C3b: complement fixation – pathogen binding for lysis and
phagocytosis (opsonisation: aanpassen aan het oppervalk van een
pathogen zodat het opgenomen kan worden door
fagocyten)
Complement activation leads to deposition of C3b
on the bacterial cell surface CR1 on
macrophage binds C3b on bacterium
endocytosis membrane-bounded vesicle is formed the
phagosome lysosomes fuse with phagosome forming the
phagolysosome
o C3a: anaphylatoxins (opening of the blood vessels) – induce
inflammation by recruitment of activation of innate immune
cells
Recruitment of inflammatory cell (anaphylatoxins): see above
Opsonization of pathogens (complement fixation): see above
Perforation of cell membrane: membrane attack complex
(MAC) induces pore formation in membrane leading to
lysis
death of pathogen
Different pathways
to infection
Lines of defense
1. Barriers: If there is an opening the pathogen can
enter and come in contact with innate immune
response.
Found in skin, gut, lungs, eyes, nose, oral cavity
o Mechanical barrier: epithelial cells joined by
tight junctions, flow of air or fluid
o Chemical barrier: fatty acids, antimicrobial
peptides and low pH
o Microbiological barrier: normal microbiota
2. Innate immunity: phagocytosis, complement, interferon,
inflammation, fever
What plays a role?
1. Soluble molecules: the complement system
Complements are proteases proteins present in
circulation and tissues and are present in inactive form.
They consist of plasma proteins (30 different forms) with
enzymatic activity.
Alternative pathway, MBL pathway (lectin pathway),
Classical pathway complement activation
cleavage C3 into C3b and C3a:
o C3b: complement fixation – pathogen binding for lysis and
phagocytosis (opsonisation: aanpassen aan het oppervalk van een
pathogen zodat het opgenomen kan worden door
fagocyten)
Complement activation leads to deposition of C3b
on the bacterial cell surface CR1 on
macrophage binds C3b on bacterium
endocytosis membrane-bounded vesicle is formed the
phagosome lysosomes fuse with phagosome forming the
phagolysosome
o C3a: anaphylatoxins (opening of the blood vessels) – induce
inflammation by recruitment of activation of innate immune
cells
Recruitment of inflammatory cell (anaphylatoxins): see above
Opsonization of pathogens (complement fixation): see above
Perforation of cell membrane: membrane attack complex
(MAC) induces pore formation in membrane leading to
lysis
death of pathogen
Different pathways
