Phagocytosis Flashcards
autophagy (2)
- removal of unnecessary or dysfunctional components
- lysosome-dependent regulated mechanism
endocytosis (2)
- the ingestion of large particles
- the uptake of fluids or macromolecules in small vesicles
pinocytosis
- a type of endocytosis that involves the ingestion of large particles
phagocytosis
- the type of endocytosis that involves the uptake of fluids or macromolecules in small vesicles
what facilitates phagocytosis of pathogens
- complement system (C’)
what is the involved in the C’ facilitation of phagocytosis (2)
- C’ receptors
- receptors for antibodies
what are pathogens opsonized by (2)
- C3b or iC3b
- IgM/IgG
what are the receptors for opsonization ligands (4)
- CR1
- CR3
- CR4
- Fc-gamma
what is the ligand for CR1 (2)
- C3b
- C4b
what is the ligand for CR3
- iC3b
what is the ligand for CR4
- iC3b
what is the ligand for Fc-gamma
- IgG
describe the interaction between the bacterium and the phagocyte during phagocytosis (2)
- initial interaction is electrostatic and involves divalent cations
- interaction is then facilitated by opsonins
phagocytosis: what does uptake involve (2)
- microfilament rearrangements
- formation of a phagosome membrane
what does the act of phagocytosis result in
- activation of the respiratory/oxidative burst
what does the respiratory/oxidative burst involve (2)
- NADPH oxidase host cell enzyme
- electron transport chain
NADPH oxidase role (2)
- enzyme moves from cytosol to the phagosome membrane
- transfers electrons from NADPH in the cytosol across the vacuole membrane
oxygen-dependent killing (2)
- transfer of electrons reduces oxygen (O2) to superoxide (O2-)
- results in productive of reaction oxygen and nitrogen species
what does oxygen-dependent killing damage inside of the phagosome (3)
- DNA
- protein
- lipids
reactive oxygen species (4)
- superoxide
- hydrogen peroxide
- hypochlorite
- hydroxyl radicals
reactive nitrogen species (3)
- nitric oxide
- peroxynitride
- nitrogen dioxide
oxygen-dependent killing: how is superoxide (O2-) produced
- NADPH oxidase converts O2 and NADPH to O2-
oxygen-dependent killing: how is hydrogen peroxide produced
- superoxide dismutase converts superoxide (O2-) to hydrogen peroxide (H2O2) using protons (H+)
oxygen-dependent killing: how are hydroxyl radicals created
- hydrogen peroxide (H2O2) combines with superoxide (O2-) to produce hydroxyl radicals (OH)
oxygen-dependent killing: how is hypochlorite created
- myeloperoxidase converts hydrogen peroxide (H2O2) into hypochlorite (OCl-) using Cl-
oxygen-dependent killing: how are singlet oxygens made
- hypochlorite (OCl-) and hydrogen peroxide (H2O2) combine to form a single oxygen (1O2)
oxygen-independent killing (6)
- acid pH
- lysozyme
- cationic proteins
- bacteriostatic molecules
- acid hydrolases
- fusion with lysosome
oxygen-independent killing: acid pH (2)
- vacuolar ATPase pumps H+ into the phagosome to create a acid pH environment
- affect the bacterial surface
oxygen-independent killing: lysozyme
- dissolves the cell of certain Gram-positive bacteria
oxygen-independent killing: cationic proteins
- bactericidal activity/damages bacteria
oxygen-independent killing: bacteriostatic molecules (2)
- lactoferrin sequesters iron
- vitamin B12-binding proteins sequesters B12
oxygen-independent killing: acid hydrolases
- post-mortem digestion of the microorganism
oxygen-independent killing: fusion with lysosome (2)
- activation of lysosomal enzymes
- acid hydrolases, cationic antimicrobial peptides, and lysozyme
oxygen-independent killing: result (2)
- bacteria are killed and digested
- damage to cell wall, cell membrane, and DNA
vacuole (3)
- space or vesicle within the cytoplasm of a cell
- enclosed by a membrane
- typically containing fluid
how is oxygen-independent killing initiated (3)
- drop in pH of the vacuole
- phagosome fuses with lysosomes
- results in activation of lysosomal enzymes
lysosomal enzymes (3)
- acid hydrolases
- cationic antimicrobial peptides
- lysozyme
what cells carry out phagocytosis (4)
- monocytes
- macrophages
- dendritic cells
- neutrophils
what cell is the most efficient phagocyte
- neutrophils
neutrophil characteristics (2)
- kill efficiently
- short half-life compared to monocytes/macrophages
TB: phagocytosis normally (3)
- two-step acidification
- degradation
- presentation of microbial peptides
TB: phagocytosis with Mtb (4)
- acidification is blocked
- no degradation
- no presentation of bacterial peptides
- no lysosomal fusion
co-localization graph: E. coli and phagocytosis
- E. coli co-localizes with the lysosomes in the graph (green and red combine to form orange)
co-localization graph: Mtb and phagocytosis
- Mtb and lysosome do not co-localize (green and red do not combine to form orange)
what is an important molecule secreted by Mtb
- protein tyrosine phosphatase A (PtpA)
protein tyrosine phosphatase A: secretion
- one of two mycobacterial secreted tyrosine phosphatases in Mtb
protein tyrosine phosphatase A (2)
- essential for Mtb ability to replicate in human macrophages
- substrate is located in the host
PtpA and Mtb: in-vitro gene knock-out (2)
- mutant was indistinguishable from its parental strain
- highlights how PtpA is not important in-vitro
PtpA and Mtb: in-vivo gene knock-out, competitive infection (2)
- macrophage was able to clear the PtpA knockout more easily than the WT Mtb
- suggest that PtpA is a key molecule in defending against the host immune system
PtpA and Mtb: in-vivo gene knock-out, independent growth (2)
- WT Mtb and complemented mutant showed better growth compared to PtpA mutant
- suggest that PtpA is a key molecule in growth inside the host system
PtpA and Mtb: in-vivo knock-out, mouse model (2)
- PtpA mutants are indistinguishable from the WT and complemented Mtb
- suggests that PtpA is only essential for Mtb replication in humans
how was the substrate for PtpA determined (2)
- construction of “trapping” mutant protein to “fish” the cognate substrate
- mutant protein does not release the substrate
how was the trapping mutant found when trying to determine the PtpA substrate (2)
- showed a higher band on Western Blot compared to WT
- indicates that the substrate is trapped
what trapping PtpA mutant was used to find the host substrate (2)
- D126A mutant
- mutant in the function of protonation of the phenolic group
what is the host substrate for PtpA (2)
- human vacuolar protein sorting protein VPS33B
- macrophage ATPase subunit H
how does PtpA function in the host: VPS33B (2)
- upon infection, PtpA binds to VPS33B
- inhibits phagolysosome fusion
how does PtpA function in the host: ATPase subunit H
- prevents normal ATPase action of driving proton transport to reduce pH
how does PtpA function in the host: VPS33B and ATPase
- blocks recruitment of substrates to the Mtb phagosome
