Phagocytic cells Flashcards
Define phagocytosis
The mechanism where most interactions between
microorganisms and the immune system occur
What are neutrophils + function
Neutrophils are short-lived white blood cells which contain a high amount of granules. Its function is to kill bacteria through phagocytosis and degranulation.
What are the 2 ways a neutrophil can die?
1) Apotosis; the neutrophil seperates itself into smaller apotopic bodies and is picked up by a macrophage and gets phagocytosed
2) Necrosis
Why is Apotosis better?
Neutrophil apoptosis prevents excessive tissue damage in inflammation and prevents the release of inflammatory alarm/danger signals
What are the 4 types of granula in neutrophils in order of degranulation?
Secretory (vesicles), Gelatinase, Specific, Azurophilic
Define what macrophage are + function
Macrophages are monocytes that have migrated from the bloodstream into any tissue in the body. Its function is to ingest and degrade dead cells, debris, tumor cells, and foreign materials.
Describe phagocytosis in 4 steps
1) Recognition and adhesion. The phagocyte binds to the microbe using receptors
2) Internalization. A pseudopods is formed and encloses the microbe which forms a phagosome.
3) Phagolysosome fusion is when lysosomes fuses with the phagosome
4) Killing. Degradation of the microbe by e.g. lysosomal enzymes
What are some positive effects that a phagocyte gets after phagocytizing a prey?
-Increased phagocytosis; several preys may be internalized
-Increased oxidative killing
-Cytokine production
-Presentation of antigens to the adaptive IS
Once a macrophage is activated, several different proteins are produced which leads to different effector functions, which?
Killing of microbes, Thrombosis, Tissue remodeling, Inflammation/Adaptive immunity, and enchanced antigen presentation
Phagocytosis is enhanced by opsonization, what are foure opsonins that aid in phago etc?
- Antibodies (adaptive)
- C3b (complement; innate)
- Mannose-binding lectin
- Surfactant proteins A and D (SP-A, SP-D)
What is opsonization?
An immune process where opsonins are used to tag foreign pathogens for elimination of phagocytes
Phagocytes recognize PAMPs, what do they bind to?
PRM
What are mannose receptors?
A c-type lectin that binds to carbohydrate motifs on bacterial, fungi, and viral surfaces.
What are glucan receptors?
Binds to glucan, a major cell wall component in bacteria & fungi
What are Scavenger receptors?
They recognize surfaces with a negative charge. (LPS)
What are Toll-like receptors?
They are specialized in recognition and signalling and they are able to recognize molecular patterns that aren’t present in vertebrates.
What are Intercellular NOD proteins?
Intercellular NOD proteins sense the presence of bacteria by recognizing bacterial peptidoglycan and induce the expression of pro inflammatory genes.
Present inside of the cell.
In the killing of phagocytic prey/pathogens there are 2 ways, oxygen dependent and independent, describe both.
- In oxygen independent
(1) Recognizes PAMPS & adheises of microbe to PRR on macrophage. (2) Internalization with the help of pseudopodia that encloses the microbe, forming a phagosome.
(3) fusion of phagosome with lysosome, forming a phagolysosome. (4) killing and digestion of microbe with the help of proteolytic/lysosomal enzymes (degrades bacterial cell wall), antimicrobial peptides.
(5) exocytosis of indigestible & residue material. - In oxygen dependent, when there is low pH in the phagosome and / or the plasma membrane the NADPH oxidase enzyme activates. And it forms super oxygen radicals (superoxide) within the lumen of
the phagolysosome. → extremely bactericidal radicals.
-> the cell will have a respiratory burst
What are 2 ways an ROI can kill a microbe?
- ROI oxidizes important components of the microbe which leads to cell death
- ROI causes influx of KT into phagosome,this leads to an increase in pH. A higher pH is beneficial to the activity of anti microbial peptides and protein.
What are 3 ways a ROI can cause tissue damage?
- the ROI damages the cell membrane which leads to cell death
- It can cross link proteins which leads to the inactivation of enzymes.
- It’s can cause fragmentation of DNA which leads to tumor development or cell death
What are the 2 leukocytes in the innate system and describe their functions?
- dendritic cells and NK-cells
- Dendritic cells are antigen presenting cells that initiates the adaptive system. An immature DC collects antigens via macropincytosis and then migrates to a regional lymph node to mature. There it activates the naive T-cells.
- NK-cells are lymphoid cells that lyses viruses infected cells and cancer cells. It activates by attaching itself to a cell and check it’s antigen presentation on the MHC class 1 receptor. When activated, it will release granules that lyses the cell. MHC 1 receptors usually are on normal cells.
How do pathogens avoid phagocytosis?
By killing the phagocyte, avoiding opsonization and paralyzing the cytoskeleton pathogens can avoid it. They can use capsules as well until it’s opsonized by antibodies.
How do pathogens avoid killing by phagocytes?
By stopping the phagosome-lysosome fusion, through resistance, and by entering cells without being noticed.
How do pathogens avoid the complement system?
By having a thick cell wall and destroying or mimicking complement proteins.
There are 2 types of immunodeficiency, name them and define them.
- Primary, which is due to a genetic defect.
- Secondary, which is caused by outside factors such as HIV
Name and describe (briefly) two different enzyme
systems via which free radicals can be formed by phagocytes.
NADPH oxidase oxidizes NADPH, forming superoxide anion which is a toxic oxygen radical. SOD (superoxide dismutase) converts the superoxide onion to hydrogen peroxidase which also is a toxic
oxygen radical.
