What does complement work more effectively with?
bacterial infection than parasitic or viral
How are complement proteins activated (simple?)?
cleaved
What is produced when complement proteins are cleaved?
2 cell fragments, a and b
Which fragment of the complement protein is smaller?
a
What are the functional categories of complement proteins?
- initiators
- enzymatic mediator
- opsonins
- inflammatory mediators
- membrane attack proteins
- receptor proteins
- regulatory proteins
What do initiators do?
initiate complement cascade
What do enzymatic mediators do?
cleave and activate other complement proteins
What do opsonins do?
enhance phagocytosis
What do inflammatory mediators do?
enhance blood supply to areas of infection
What do membrane attack proteins do?
form membrane attack complexes called MACs
What do receptor proteins do?
located on cell surfaces, bind other complement proteins
What do regulatory proteins?
protect healthy cells from effects of complent
What 3 ways does complement activation occur?
- classical pathway
- lectin pathway
- alternative pathway
What is the classical pathway of activation?
- antigen-antibody complexes bind initiator proteins which activates complement cascade
- considered adaptive immunity because utilizes antibodies
What is the lectin pathway of activation?
- initiator proteins bind to lectins on bacteria
- activates complement cascade
What is the alternative pathway of activation?
- complement cascade is initiated with spontaneous cleavage of C3 (complement protein 3)
What is lectin?
carbohydrate structures
What are the 3 functions of complement?
- Membrane attack complex (MAC)
- Opsonization
- Promotion of inflammation
What does Membrane Attack Complexes do?
- complement proteins embed into bacterial cell membrane
- causes holes to form in bacterial membrane
- water and salts diffuse into cell causing cell to burst
What is opsonization?
- cleaved complement proteins can bind to bacteria, marking it for phagocytosis
- receptors on phagocytic cells bind to complement protein opsonins and this initiates phagocytosis
How does complement promote inflammation?
smaller complement fragments bind to receptors on innate immune cells
What does smaller complement fragments binding to receptors on inmate immune cells result in?
- release of TNF-alpha and IL-6
- degranulation of granulocytes
What does the release of TNF-alpha and IL-6 result in?
increase in vascular permeability and vasodilation
What are the granulocytes?
neutrophils, eosinophils, basophils, mast cells
