Disorders of Phagocytosis
المؤلف:
APURBA S. SASTRY , SANDHYA BHAT
المصدر:
Essentials Of Medical Microbiology 2021
الجزء والصفحة:
3rd edition , p211-212
2025-09-29
442
Chronic Granulomatous Disease (CGD) Pathogenesis
Pathogenesis of CGD involves inherited defects in the gene encoding components of oxidase system, e.g. Nicotinamide adenine dinucleotide phosphate (NADP) oxidase of phagocyte which breaks down hydrogen peroxide to generate free oxygen radicals (O2-) that are involved in microbial killing. As a result, there occurs decreased oxidative burst which predisposes to recurrent bacterial infections. CGD is a genetic disease that runs in family in two forms:
- In X-linked form (more common, 70%), membrane component of phagocyte oxidase is defective
- In autosomal recessive form, cytoplasmic component of phagocyte oxidase is defective.
Manifestations
- The bacteria involved in the recurrent infections are catalase positive; pyogenic pathogens such as staphylococci, Pseudomonas and coliforms. Catalase negative pathogens such as streptococci and pneumococci are handled well
- Patients also undergo excessive inflammatory reactions that result in gingivitis, swollen lymph nodes, and nonmalignant granulomas (lumpy subcutaneous cell masses)
- Nitroblue tetrazolium reduction test (NBT) is used as screening test to detect deficiency of NADPH oxidase activity.
Myeloperoxidase Deficiency
It is a common genetic disorder characterized by deficiency in either quantity or function, of myeloperoxidase, an enzyme produced by neutrophils. Patients present with immune deficiency and recurrent infections, especially with Candida albicans.
Chediak–higashi Syndrome
It is an autosomal recessive disease, characterized by:
- Defective fusion of phagosomes and lysosomes in phagocytes which leads to increased susceptibility to recurrent and severe pyogenic infections
- Abnormalities in melanocytes leading to albinism (lack of skin and eye pigment) Abnormalities in cells of the nervous system (associated with nerve defects), and
- Platelets abnormalities, causing bleeding disorders
- Aggressive but non-malignant infiltration of organs by lymphoid cells.
Genetic defect: Pathogenesis of this syndrome is due to a mutation in a protein called LYST which is believed to regulate lysosomal trafficking.
- The mutation impairs the targeting of proteins to secretory lysosomes, which makes them unable to lyse bacteria
- Phagocytes from patients with this immune defect contain giant granules but do not have the ability to kill bacteria.
Leukocyte Adhesion Deficiency (LAD)
LAD is rare autosomal recessive disorder, characterized by a defect in the adhesion of leukocytes which results in poor leukocyte chemotaxis particularly of neutrophils. Thus it predisposes to various bacterial and fungal infections. LAD is due to mutations in β2 integrin subunit (CD18) of the leukocyte cell adhesion molecule or fucosyltransferase enzyme.
Lazy Leukocyte Syndrome
It is an idiopathic condition due to defect in neutrophil chemotaxis which results in increased pyogenic infections such as gingivitis, abscess formation, pneumonia and neutropenia.
Job’s Syndrome (hyper-IgE Syndrome)
Hyper-IgE syndrome is a rare primary immunodeficiency disease characterized by eczema, recurrent staphylococcal skin abscesses, recurrent lung infections (pneumatocele), eosinophilia and high serum levels of IgE. Underlying mechanism of this immunodeficiency disease is defect in neutrophil chemotaxis; due to mutations in either STAT3 or DOCK8 genes.
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