Chronic granulomatous disease

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Chronic granulomatous disease

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Aspergillus spp.

chronic granulomatous disease p. 107

Chronic granulomatous disease (CGD) p. NaN

catalase-positive microbes p. 183

immunodeficiencies and p. 115

recombinant cytokines for p. NaN

respiratory burst in p. 107

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With chronic granulomatous disease, granulomatous refers to the development of small nodules called granulomas.

Granulomas are collections of immune cells, especially phagocytes, which cluster together when they can't kill invading pathogens, like bacteria or fungi.

So chronic granulomatous disease is an immunodeficiency where phagocytes are unable to kill pathogens, and instead they form granulomas throughout the body.

Normally, when a pathogen invades the body, phagocytes, like neutrophils and macrophages, are the first on the scene.

When a phagocyte detects a pathogen, it stretches itself out as if it had two little arms.

These arms wrap around the pathogen and seal themselves back up, forming a vesicle inside the phagocyte called a phagosome.

Because the phagosome is lined by what was previously part of the phagocyte's surface membrane, whatever structures were previously surface-bound, like this protein complex called NADPH oxidase, end up inside the phagosome.

The phagocyte also has other organelles, like lysosomes, which are full of digestive enzymes that can destroy a pathogen.

When a lysosome fuses with a phagosome, it forms a phagolysosome, and lysosomal enzymes start to destroy the pathogen.

The lysosomal enzymes also activate NADPH oxidase, which came from the phagosome, causing NADPH to undergo oxidation, and lose one of its electrons.

Nearby oxygen molecules can grab these electrons to become reduced and form superoxide ions, or O2- ions.

Another enzyme, superoxide dismutase, can take these ions and combine them with hydrogen ions to form hydrogen peroxide, or H2O2.

This process of producing superoxide ions and hydrogen peroxide is called the respiratory burst.

These ions and molecules destroy pathogens by damaging their cell membranes and proteins.

In chronic granulomatous disease, there’s a mutation in the genes that code for NADPH oxidase, so the enzyme is less functional.

One common mutation is an autosomal recessive mutation, which is where both copies of a chromosome need to possess the same mutation for the disease to occur.

Another common mutation is an X-linked recessive mutation, and since men only have one X chromosome, they get the disease, whereas because women have two X chromosomes, they only get the disease if both of their X chromosomes are affected which is much less likely.

Summary

Chronic granulomatous disease (CGD) is a genetic condition, in which neutrophils and macrophages cannot create superoxide radicals to kill engulfed germs. There is a mutation in NADPH oxidase genes. People with CGD have problems fighting infections because they don't have enough neutrophils to fight bacteria and other germs.

People with CGD often get recurrent and severe infections, especially in their lungs, ears, and sinuses. They may also develop skin abscesses or sores that don't heal properly. People with CGD struggle to fight off infections caused by catalase-positive bacteria, such as S. aureus, Serratia, Klebsiella, Aspergillus, and Burkholderia.

Sources

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  2. "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
  3. "Yen & Jaffe's Reproductive Endocrinology" Saunders W.B. (2018)
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  5. "Robbins Basic Pathology" Elsevier (2017)
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  7. "How does the oxidative burst of macrophages kill bacteria? Still an open question" Molecular Microbiology (2011)
  8. "Hydrogen peroxide: a potent cytotoxic agent effective in causing cellular damage and used in the possible treatment for certain tumours" Medical Hypotheses (2001)