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DESCRIPTION
phagiTRANSCRIPT
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Phagocytosis
A. Recognition & attachment of particle to be ingested
B. Engulfment - formation of phagocytic vacuole
C. Killing or degradation
1. Recognition & attachments:
Leucocytes recognize microbes and dead cells by receptors
a. Mannose receptor -bind mannose and fucose residues of
glycoprotein in microbial cell wall
b. Scavenger receptors - originally defined as molecules that bind
modified LDL particles. Also bind microbes
c. Mac 1 integrins
Efficiency of phagocytosis increased by opsonization.
Opsonins
Bind to specific receptors on leukocytesReceptors
- Fe fragment of IgG Fc gamma R1
- C & C CR 1, 2, 3
- Plasma proteins:
1. Mannose binding lectins C1q
2. Fibrinogen
3. Fibronectin Integrins
4. C-Reactive proteins
Neutrophils & macrophages: can recognize engulf bacteria & extraneous
matter (in absence of opsonins)
2. Engulfment:
a. Pseudopods of phagocyte flow around the microbe to be
engulfed Microbe enclosed in a phagosome
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b. Phagosome fuses with lysosome phagolysosome
c. Degranulation into phagolysosome and bacterial killing.
d. Biochemical events of engulfment same as chemotaxis Killing
3. Degradation
a. Mainly: O dependent Mechanisms
i. Activation of NADPH oxidase
ii. HOCl: - Halogenation
iii. Peroxidation
b. Lesser known mechanism is H O - MPO - halide: - but its the most.
efficient bactericidal system -effective. against fungi, viruses, protozoa,
helminths
Example
Which of the following is most important in the bactericidal activity?
AIPG 2011
A. Hydrolase
B. Peroxidase
C. Transferase
D. Dismutase
Solution
B. Peroxidase
c. Dead organism
Study(Http://Gradestack.Com/Dr-Bhatia-Medical-Coaching-Institute/Pathology/3168/Subject-Study)
1. Cell Injury(http://gradestack.com/Dr-Bhatia-Medical-Coaching-Institute/Causes-Of-Cellular-Injury/16081-3168-9159-study-wtw)
2. Inflammation(http://gradestack.com/Dr-Bhatia-Medical-Coaching-Institute/Response-Of-Vascularized-Connective-Tissue-To/16082-3168-9317-study-wtw)
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Comment
a. lysosomal hydrolases
b. MPO deficient leukocytes: superoxide, hydroxy singlet oxygen
c. O - independent Mechanism: through action of substances in
leukocyte granules
i. Bactericidal permeability increasing protein (BPI) -
phospholipase activation, permeability
ii. Lysozyme- hydrolyses the glycopeptide coat of bacteria
iii. Lactoferrin
iv. Major basic protein: Eosinophils
v. Cytotoxic to many parasites
vi. Defensins:
pH of phagolysosome: 4 5
d. Release of leukocyte products
Mechanism of release:
a. Regurgitation during feeding: If Phagocytic vacuole remains
transiently open to outside
b. Frustrated phagocytosis: on flat surface (e.g. GBM ~ immune
complexes)
c. Surface phagocytosis: Mech. by which phagocytes facilitate
ingestion of bacteria & other foreign material by trapping it
against resistant surface
d. Cytotoxic release: After phagocytosis of potentially
membranolytic substances (e.g crystals)
e. Exocytosis: Secondary granules of neutrophils After
phagocytosis - apoptotic cell death and engulfment of Neutrophil
by monocyte
3. Neoplasia(http://gradestack.com/Dr-Bhatia-Medical-Coaching-
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