Phagocytosis
Phagocytosis - cell uptake of large particles visible in a microscope( eg, microorganisms, large viruses, damaged cell bodies, etc.).The process of phagocytosis can be divided into two phases. In the first phase, the particles bind to the surface of the membrane. In the second phase, the actual absorption of the particle and its further destruction occur. There are two main groups of phagocyte cells - mononuclear and polynucleated. Polynuclear neutrophils constitute
the first line of defense against the penetration of various bacteria, fungi and protozoa into the body. They destroy the damaged and dead cells, participate in the process of removing old red blood cells and cleaning the wound surface.
The study of indicators of phagocytosis is important in the complex analysis and diagnosis of immunodeficient conditions: often recurrent purulent inflammatory processes, long-term healing wounds, propensity to postoperative complications. The study of the phagocytosis system helps in the diagnosis of secondary immunodeficiency states caused by drug therapy. The most informative for assessing the activity of phagocytosis is the phagocytic number, the number of active phagocytes and the index of completeness of phagocytosis.
Phagocytic activity of neutrophils
Parameters characterizing the state of phagocytosis.
■ Phagocytic number: norm - 5-10 microbial particles. The phagocytic number is the average number of microbes absorbed by a single blood neutrophil. Characterizes the absorption capacity of neutrophils.
■ Phagocytic blood capacity: the norm is 12.5-25x109 per 1 liter of blood. Phagocytic blood capacity is the number of microbes that can absorb neutrophils 1 liter of blood.
■ Phagocytic index: the norm is 65-95%.The phagocytic index is the relative amount of neutrophils( expressed as a percentage) involved in phagocytosis.
■ The number of active phagocytes: the norm is 1.6-5.0 × 109 in 1 liter of blood. The number of active phagocytes is the absolute number of phagocytic neutrophils in 1 liter of blood.
■ Index of phagocytosis completeness: the norm is more than 1. The index of phagocytosis completeness reflects the digestive capacity of phagocytes.
Phagocytic activity of neutrophils usually increases at the onset of the inflammatory process. Its reduction leads to chronic inflammation and maintenance of the autoimmune process, as the function of destruction and removal of immune complexes from the body is disrupted.
Diseases and conditions at which the phagocytic activity of neutrophils change are presented in Table. .
Table Diseases and conditions in which the phagocytic activity of neutrophils changes
Table Diseases and conditions at which the phagocytic activity of neutrophils changes
Spontaneous test with NST
Normally,adults the number of HCT-positive neutrophils is up to 10%.
Spontaneous test with NST( nitrosinium tetrazolium) allows to evaluate the state of oxygen-dependent bactericidal mechanism of phagocytes( granulocytes) of blood in vitro. It characterizes the state and degree of activation of the intracellular NADP-H-oxidase antibacterial system. The principle of the method is based on the restoration of the absorbed phagocyte soluble HCT dye into insoluble diformazan under the influence of superoxidanion( intended for intracellular destruction of the infectious agent after its absorption), formed in the NADPH-oxidase reaction. Indicators of the NST-test are increased in the initial period of acute bacterial infections, whereas in the sub-stroma and chronic course of the infectious process they decrease. Sanitation of the organism from the pathogen is accompanied by the normalization of the indicator. A sharp decline indicates a decompensation of anti-infectious protection and is considered a prognostically unfavorable sign.
The NST test plays an important role in the diagnosis of chronic granulomatous diseases, which are characterized by the presence of defects in the NADP-H-oxidase complex. Patients with chronic granulomatous diseases are characterized by the presence of recurrent infections( pneumonia, lymphadenitis, lung, liver, skin abscesses) caused by Staphylococcus aureus, Klebsiella spp., Candida albicans, Salmonella spp., Escherichia coli, Aspergillus spp., Pseudomonas cepacia, Mycobacterium spp.and Pneumocystis carinii.
Neutrophils in patients with chronic granulomatous diseases have normal phagocytic function, but due to a defect in the NADP-H-oxidase complex they are not capable of destroying microorganisms. Hereditary defects of NADP-H-oxidase complex are in most cases adhered to chromosome X, less often autosomal recessive.
Spontaneous test with NST
Reduction of spontaneous test with NST is characteristic for chronic inflammation, congenital defects of the phagocytic system, secondary and primary immunodeficiencies, HIV infection, malignant neoplasms, severe burns, trauma, stress, malnutrition, treatment with cytostatics and immunosuppressants,ionizing radiation.
An increase in the spontaneous test with NST is noted for antigenic irritation due to bacterial inflammation( prodromal period, acute infection period with normal phagocytosis activity), chronic granulomatosis, leukocytosis, enhancement of antibody-dependent cytotoxicity of phagocytes, autoimmune diseases, allergies.
Activated test with NST
Normally, the number of HCT-positive neutrophils in adults is 40-80%.
Activated test with NST allows to evaluate the functional reserve of the oxygen-dependent bactericidal mechanism of phagocytes. The test is used to identify the reserve capacity of intracellular phagocyte systems. With preserved intracellular antibacterial activity in phagocytes, there is a sharp increase in the amount of formazan-positive neutrophils after their stimulation with latex. Reduction of the parameters of the activated HCT-test of neutrophils below 40% and monocytes below 87% indicates a lack of phagocytosis.