Lecture 5&6 phagocytosis and complement system Flashcards
ability of some cells to ingest foreign particles
phagocytosis
are a class of cells which are capable of ingestion and killing of microorganisms that incite inflammation response
phagocytes
first to accumulate around the invaders and initiate the phagocytic process are ___________.
Later, local and blood borne ________ also migrate to the tissue sit of initiate phagoycytosis
neutrophils (suicide bombers)
macrophage(seriel killers)
what are the professional phagocytes
neutrophils
macrophage
list the sequence of events involved in phagocytosis/destruction of engulfed
1.chemotaxis
2. adherence
3. ingestion
4. destruction
egestion (only in the case of macrophages)
delivery of phagocytic cells to the site of infection
chemotaxis
phagocytic adherence to the target
adherence
engulfment of the target particle
ingestion
intracellular killing and digestion of the target
destruction
additional step to remove dead material before macrophages start to kill again
egestion
coating of a hydrophilic material with opsonins that include IgG, IgM, C3b
** make bacteria tasty for neutrophil/macrophages
opsonization
neutrophil can phagocytose anything more _________ than itself
hydrophobic
neutrophils don’t bind hydrophilic material
what are the 2 types of coating possible through opsonization
antibody
complement
the 2 neutrophil membrane receptors important in phagocytosis
Fc receptors
C3b receptors
bind antibody that is bound to an antigen, especially IgG antibody
Fc receptors
bind to C3b when it is coating bacteria
C3b receptor
once neutrophil bind to opsonized material, it is readily engulfed forming a _______________
phagosome
membrane bound vesicle (compartment) containing the ingested microbe or material
phagosome
formation of the phagolysosome
phagosome migrates into cytoplasm and collides with lysosomal granules which explosively discharge their contents into the membrane enclosed vesicle (phagosome)
membranes of phagosome and lysosome actually fuse resulting in a digestive vacuole called the phagolysome
what happens in the phagolysosome
killing and digestion of engulfed microbe take place
why does destruction of microbe only occur inside the phagolysosome
its so that the toxic substances and lethal activities of the phagocytes are turned against themselves
after phagolysosome formation the first detectable effect on bacterial physiology is the loss of ________.
By 10 to 30 min after ingestion many pathogenic/nonpathogenic bacteria are _______ followed by lysis and digestion of bacteria by _____________
viability
lysis
lysosomal enzymes
What are the 3 intracellular killing processes
- lytic enzymes and antimicrobial peptides from granules
- oxidative metabolism (respiratory burst)
- neutrophil extracellular traps
list the primary granules
hydrolases
lysozyme
defensins
myeloperoxidase
list the secondary granules
lysozyme
lactoferrin
collagenase
breaks covalent bonds by adding water, important for degrading dead bacteria or dead tissues
hydrolases
breaks down peptidoglycan in gram-positive bacteria
found in many secretions in the body
lysozyme
small cationic proteins that kill bacteria, especially gram-positive, that are 29-42 amino acids long and have hydrophobic outside and hydrophilic interior and inserts into a membrane to form a pore
also called antimicrobial peptides
defensins
an enzyme that has an important role in the oxygen mediated killing mechanism
myeloperoxidase
chelates iron
lactoferrin
degrades connective tissue, so it can move through to the site of inflammation
collagenase
most potent killing mechanism of neutrophil
oxygen mediated killing mechanism (myeloperoxidase)
where does oxygen mediated killing mechanism occur and what products does it kill
occurs in phagolysome
killing products of respiratory burst include:
1. hypochlorite
2.hydrogen peroxide
3. aldehydes
4.oxygen radicals
removal of dying of neutrophils by macrophages
macrophage and neutrophil interact by CD31
if neutrophil “acknowledges” macrophage= healthy neutrophil and macrophage leaves neutrophil alone
if neutrophil DOES NOT “acknowledge” macrophage= neutrophil is dying and macrophage kills neutrophil
M2 cells
clean up crew
alternative activation
increases tissue repair, increases MHC class 2 expression, and reduces microbial killing
M1 cells
phagocytic cells- macrophages
classical activation
increased- size, movement, MHC 2 expression, lysosomal enzymes, NO production
what do stimulated neutrophils release extracellularly? ___________ and ____________
what does this extracellular degranulation create?
nuclear material
granular proteins (DNA, histone, granular material)
mesh that traps the bacteria and the antimicrobial proteins kill the bacteria (NETosis)
a group of serum and cell surface proteins activated by factors such as the combination of antigen and antibody resulting in the generation of enzyme cascades that have a variety of biological consequences including cell lysis and opsonization
complement
what are the 3 pathways that activate complement
- classical pathway
- alternative pathway
- MB-Lectin pathway
what activates classical pathway
when a complement fixing antibody (IgM, IgG) binds antigen
binding site for complement on Fc portion of the antibody “opens up” when the antibody is bound to antigen
what activates lectin pathway
initiated by soluble pattern recognition molecules (PRR) that bind to carbohydrates on the microbial surface
this activates enzymes that activate complement
(MBL binds to mannose on pathogen)
what activates alternative pathway
initiated by C3b binding on the cell wall of pathogens
C3 spontaneously breaks down to C3a and C3b
classical pathway is involved in what kind of immunity
innate and adaptive
alternative pathway is involved in what kind of immunity
part of the innate immunity
**adaptive immunity is not required for this pathway to be initiated
MB-Lectin pathway is involved in what kind of immunity
part of the innate immunity; adaptive is not required to initiate this pathway
Mammalian cells do not have ____________ on their cell surface, so MBL pathway is initiated on microbes but not self-cells
mannose
how do the three complement pathways differ
when are they the same
differ in the initiation of the cascade
pathways are the same from C3 through terminal pathway and formation of membrane attack complex
describe the process:
initiation of the classical pathway
- antigen-antibody binding initiates the classical pathway
- when antigen binds with antibody, theres is a conformational change in the Fc portion of the antibody that allows C1 (first protein of complement cascade to bind to antigen-antibody complex
must be 2 Fc binding sites for C1 to bind, so one IgM or 2 IgG needed for initiation*
- activated C1 cleaves C4 into C4a and C4b
- C4b binds to a membrane and C2 binds to membrane bound C4b
- activated C1 cleaves C2 when its bound to C4b leading to formation of C4b2b (classical pathway C3 convertase)
- C3 convertase cleaves into a and b; C3b is an opsonin
- C3b binds C5 and then C4bC2b cleaves C5 leading to initiation of terminal pathway
describe the process:
activation of alternative pathway
- C3 spontaneously breaks into C3a and C3b
- C3b’s reactive carbonyl group will covalently bind to cell surface
- Factor B can bind to C3b
4.Factor D can cleave factor B bound to C3b
5.C3bBb is the alternative pathway C3 convertase
describe the process:
activation of MBL pathway
** mannose binding lectin (MBL) is a soluble PRR**
1. MBL binds to mannose (a PAMP) on microbes
2. bound MBL activates MASP-2, MBL- associated serine protease which has similar activity to C1
3. MASP-2 cleaves C4 and the cascade is initiated
why is 1 IgM more efficient than 2 IgG molecules
it has a pentameric (5 sided) shape which provides the same conformation as 2 IgG molecules
this part of the complement cascade is the same for all three pathways
terminal complement pathway
what initiates the terminal pathway
cleavage of C5
Biological consequences of complement activation:
C1 to C2a
increased vascular permiability
Biological consequences of complement activation:
C1 to C3a
anaphylatoxin
microbial killing
Biological consequences of complement activation:
C1 to C3b
immune regulation
opsonization
Biological consequences of complement activation:
C1 to C5b67
leukocyte chemotaxin
Biological consequences of complement activation:
C1 to C5a
neutrophil chemotaxis
anaphylatoxin
lysosomal enzyme secretion
neutrophil activation
increased vascular permeability
smooth muscle contraction
Biological consequences of complement activation:
C1
cell membrane lysis
3 functions of complement that eliminate microbes
- opsonization and phagocytosis
2.complement-mediated cytolysis
3.stimulation of inflammatory reactions
describe: opsonization and phagocytosis
- binding of C3b to microbe (opsonization)
- recognition of bound C3b by phagocyte C3b receptor
- phagocytosis and killing of microbe
describe: complement-mediated cytolysis
- binding of C3b to microbe, activation of late components of complement
- formation of membrane attack complex (MAC)
- osmotic lysis
describe: stimulation of inflammatory reactions
- proteolysis of C3 and C5 to release C3a and C5a
- recruitment and activation of leukocytes by C5a and C3a
- destruction of microbes by leukocytes
