Topic 9 Immune responses Flashcards
What typical properties do the innate immunity have?
It’s fast and have a non-specific defense and response to injury
What comprises the innate immunity?
Epithelial barriers (skin, mucous), acidic environment&enzymes, phagocytes, Natural killer (NK) cells, proteins & enzymes that lyse or inactivate bacteria (complement factors)
Which cells are the phagocytes?
Dendritic cells, macrophages and neutrophils
Whats the role of NK cells?
They sense virus infected cells and lyse them
Whats the role of cytokines?
They activate macrophages, neutrophils, NK cells and enhance microbial killing
What are the 3 main functions of the complement proteins?
- C3b bind. to foreign surfaces - induce phagocytosis.
- Cleaved C3b into C5a & C3a recruits and activate leukocytes that kill the microbes
- Can form the membrane attack complex (MAC)
What’s the classical pathway?
Antigen-antibody binding result in C1 binding to constant portion of antibody, cleaving into a and b fragments, followed by formation of C3 convertase and C5 convertase. Ends in formation of the Membrane Attack Complex (MAC) that inserts itself as a pore into foreign cells, causing lysis.
What’s the alternative pathway?
Starts when C3 spontaneously hydrolyses and C3b binds to a surface (if host cell = rapidly deactivated). Involves factor B and D. Formation of C3 convertase, C5 convertase and resulting in formation of Membrane Attack Complex (MAC)
Where is the Complement 3 usually found?
C3 is usually found in blood plasma/serum
What does both the alternative and classical pathway result in?
Membrane Attack Complex (MAC) formation that creates a hole in the membrane to kill the cell via osmotic lysis
Name some links between the inflammatory process and the complement system
- C1 and C3 can be activated by plasmin & Kallikrein or other by-products from coagulation
- C3-5a can activate leukocytes
- C5a chemoattractant for neutrophils and macrophages
- C3b opsonization -> recognition for phagocytes
Further explain the opsonization process
Bacteria are “opsonized” by the binding of an antibody and C3b to receptors on the phagocyte membrane - which then stimulates phagocytosis. The complex of the antibody and C3b is called opsonin.
How does the complement react to biomaterials?
Surface reaction then through the alternative pathway by C3b binding and through the classical by IgG binding and activating C1. (IgG is the most common AB)
Which two enzymes are needed for the complement to create the MAC?
First C3 convertase enzymes then C5 convertase enzymes.
How is the complement activation regulated?
Short half-life of the enzymes in the cascade. Regulatory proteins called “regulator of complement activation” (RCA) proteins