Testing of phagocyte function Flashcards
Define phagocytosis:
non-specific immune mechanism playing an essential role in host defence mechanisms through the uptake and destruction of infectious pathogens.
Phagocytosis is the process in which:
specialised cells of the immune system engulf and destroy foreign cells as well as organisms own damaged or dead cells, and so participate in the clearance of microbes and the restitution of damaged tissues
Which are the most effective phagocytic cells?
neutrophils and monocytes - immature cells circulating in the bloodstream, and
macrophages - present in various organs and tissues
Which other cells can also phagocytose?
eosinophils - small particles
dendritic cells - some particles
What is the most important role of eosinophils?
Kill multicellular parasites by release of the biologically active components on the surface of these parasites
Why is phagocytosis important for dendritic cells?
Elaboration of a specific immune response rather than for directly destroying the pathogens
What are the first inflammatory cells to enter damaged tissue from the blood after tissue damage?
neutrophils (short-lived cells)
What phases of inflammation does macrophages participate in?
sub-acute and chronic phases of inflammation, tissue restoration, wound healing, antigen presentation, cytokine production and phagocytosis
What are the stages of phagocytosis?
- Chemotaxis
- Adhesion
- Engulfment
- Destruction
- Indigestible and waste material is finally discharged from the phagocytic cell
What happens during chemotaxis? (1st step)
migration of leukocytes along the concentration gradient of chemoattractants, produced in damaged tissues or as a result of microbial invasion
What happens in adhesion (2nd step)?
Recognition of the particles to be phagocytosed by receptors expressed on the leukocyte’s surface.
Coating the particle - opsonisation of opsonins (antibodies(IgG), complement fragments, mannose-binding lectin, C-reactive protein etc.)
Receptors are coated with various proteins and give signals to activate phagocytes.
What happens during engulfment (3rd step)?
Ingestion.
Binding of a particle to phagocytic leukocyte receptors initiates the process of active phagocytosis of the particle.
Engulfment result in phagosome (a vacuole), which fuses with granules (lysosomes) containing antimicrobial substances to form a phagolysosome.
What happens during destruction (4th step)?
Antimicrobial substances digest foreign material, destroy bacteria or inhibit their growth.
These substances include products of the lysosome, acidic hydrolases, proteases, lactoferrin, bactericidal permeability-increasing protein, defensins, reactive oxygen and nitrogen intermediates.
The role of phagocytosis is crucial in the…?
Innate immune defence
What does defects in phagocyte functions result in?
Impaired protection against bacteria and fungi.
Pyogenic or granulamatous bacterial and fungal infections located in the skin, respiratory or gastrointestinal tract.
What are primary immunodeficiencies?
diseases with abnormal phagocyte number or impaired ability to migrate, engulf and destroy pathogens
What is the first step in diagnosis of failure of phagocytosis?
evaluation of neutrophil and monocyte numbers and then subsequent functional studies of the individual steps and mechanism of phagocytosis:
- ingestion
- metabolic activation (resp. burst)
- microbial activity
What is the maximum concentration of heparin for phagocytic cell function test?
10 IU per 1 ml of the blood
What is used during evaluation of ingestion?
Full-heparinised blood or isolated leukocytes using various microorganisms or microscopic hydrophilic particles as a substrate
What are the functional methods for evaluation of ingestion called?
PhA - phagocytic activity
PhI - phagocytic index
What is used for quantitative evaluation of ingestion?
Flow cytometric assays, to measure neutrophil or monocyte-associated fluorescence after incubation of whole blood with FITC-labelled E. coli
What is added to distinguish between internalised and membrane bound bacteria in evaluation of ingestion?
Trypan blue
How do you calculate PhA and PhI?
PhA = number of phagocytes with ingested particles / number of counted phagocytes x 100
PhI = number of phagocytosed C. albicans cells in 100 phagocytes / 100
Define the term ‘‘respiratory burst’’
when the consumption of oxygen dramatically increases following ingestion of microbes and activation of phagocytes, in order to produce free superoxide anion and other reactiove species