Infection and Immunity Wk 8 - Lesson 59

What is the complement system?

a set of plasma proteins produced in hepatocytes that act together in a proteolytic cascade as defense against pathogens in extracellular spaces

What part of the innate immune system is the complement system?

hummoral

How do proteases activate other proteases?

cleavage

What is the complement system triggered by?

antibodies binding to antigens (classical) and complement protein binding to surface of pathogens (alternative)

What are the two pathways in the complement system?

classical and alternative

What are the important complement proteins?

C1, C3, C5

What is the details for the classical pathway?

antibody and antigen bind and activates C1 complex -> C3 -> C5 -> membrane attack complex -> pathogen or host cell lysis

What are the details for the alternative pathway?

C3 -> C5 -> membrane attack complex -> pathogen or host cell lysis

What is a process that C3b is involved in?

C3b can be an opsonin and enhance phagocytosis and play a part in the antigen presentation to cells of adaptive immune system

Which pathway is faster?

alternative pathway

What are the functions of the complement system?

coating of pathogens with complement proteins and production of signaling molecules

What are the processes that can occur when complement proteins coat pathogens?

kill certain pathogens directly, facilitate phagocytosis, help to stimulate certain adaptive immune cells

How do complement proteins kill pathogens directly?

through the alternative pathway without the help of immune cells or antibodies

What are the steps of complement proteins killing pathogens directly?

invading microbe crosses physical barrier, microbe coated with complement protein, amplification of complement protein, formation of membrane attack complex as cytolytic pore

What pathogens are resistant to MAC and why?

gram-positive bacteria because they don't have carbohydrates on their surface for binding of the complement proteins

What are MAC most effective against?

gram-negative bacteria, nucleated cells, enveloped viruses

How do complement proteins facilitate phagocytosis?

labelling of pathogens for recognition by phagocytic cells (opsonization); neutrophils and macrophages

How long does killing pathogens directly take?

minutes

How long does facilitating phagocytosis take?

minutes to hours

What are the steps for facilitating phagocytosis?

invading microbe crosses physical barrier, microbe coated with complement protein, amplification of complement protein, binding to complement receptor on phagocytic cell and phagocytosis

How long does stimulation of adaptive immune cells take?

days to weeks

How do complement proteins produce signaling molecules?

chemotaxis and cytokines