, was led by Dr. David Underhill, Ph.D., who is the Janis and William Wetsman Family Chair in Inflammatory Bowel Disease at Cedars-Sinai in Los Angeles, California, USA.
"We were surprised to find that M. restricta was more common on intestinal tissue surfaces in Crohn's disease patients than in healthy people,"
says Underhill. "Further, the presence of Malassezia was linked to a common variation in a gene known to be important for immunity to fungi - a genetic signature more common in patients with Crohn's disease than the healthy population."
Crohn's Disease and Malassezia restricta
Crohn's disease is a type of chronic IBD
that damages the mucus lining of the gastrointestinal (GI) tract due to altered immune responses to the gut microbiome. Symptoms include abdominal pain, diarrhea, anemia, weight loss, and severe fatigue. The disease is incurable, and the mainstay of treatment is the administration of steroids and immunosuppressants to slow down disease progression.
While most studies on microbes in the GI tract are centered on bacteria, the present study focused on fungi, more specifically, the yeast M. restricta
to investigate its possible role in gut diseases such as Crohn's disease. Malassezia
yeasts normally reside in the hair follicles of the scalp and oily skin and cause skin conditions such as dandruff. However, their role in the GI tract is not well understood. It has been hypothesized that the host immune responses against these yeasts could aggravate the symptoms associated with Crohn's disease.
What Did Studies in Mice and Humans Reveal?
The gist of the major study findings in mice and humans are presented below: Mice Studies
- Early studies found the presence of fungi in the gut microbiome of mice
- The immune system in mice keeps these fungi in check and prevents inflammation in the GI tract
- Presence of M. restricta in the gut of mice exacerbates the symptoms of colitis, which is a type of IBD
- Gut mucosa-associated fungi are found in healthy individuals and Crohn's disease patients
- M. restricta is particularly elevated in the gut mucosa of Crohn's disease patients
- These Crohn's disease patients carry a genetic risk allele known as IBD CARD9
- Presence of the IBD CARD9 risk allele boosts the secretion of inflammatory cytokines by immune cells in response to M. restricta
It may be concluded that the presence of M. restricta
in the gut is not always harmful, as it is found in healthy humans and mice. However, it can worsen the symptoms of certain inflammatory disorders such as Crohn's disease.
In this regard, Underhill says: "The data so far do not suggest that the presence of Malassezia in the gut is an inherently bad thing. We found it in some healthy people, and in mice, it does not seem to cause disease in the gut by itself."
He adds: "However, if there is some intestinal inflammation, Malassezia seems to make it worse."
The researchers plan to study whether the elimination of M. restricta
from the gut microbiome in Crohn's disease patients is capable of alleviating the symptoms.
The study was funded by the National Institutes of Health (NIH), National Institute of Diabetes and Digestive and Kidney Diseases, and the National Center for Advancing Translational Sciences, USA. Reference :
- Malassezia is Associated with Crohn's Disease and Exacerbates Colitis in Mouse Models - (https://doi.org/10.1016/j.chom.2019.01.007)