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I recently read a study (Monson & Wilkinson, 1981) that said mannose in body fluids can be an indicator of an invasive candida infection and I was wondering why mannose would be elevated, is it an immune response?

References

Monson, T. P., & Wilkinson, K. P. (1981). Mannose in body fluids as an indicator of invasive candidiasis. Journal of clinical microbiology, 14(5), 557–562. https://doi.org/10.1128/jcm.14.5.557-562.1981

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    Can you please edit your question and add a link to this study you read? It's a site requirement.
    – Carey Gregory
    Aug 1 at 4:52
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For the answer, you need to find the source of the mannose.

Sharma, et al (2014) points out that

Mannose occurs in microbes, plants and animals. Free mannose is found in small amounts in many fruits such as oranges, apples and peaches [12] and in mammalian plasma at 50–100 μM [13]. More often, mannose occurs in homo-or hetero-polymers such as yeast mannans (α-mannose) where it can account for nearly 16% of dry weight [14]

[...]

  1. Herman RH. Mannose metabolism. I. Am J Clin Nutr. 1971;24:488–98. [PubMed] [Google Scholar]

  2. Alton G, Hasilik M, Niehues R, Panneerselvam K, Etchison JR, Fana F, et al. Direct utilization of mannose for mammalian glycoprotein biosynthesis. Glycobiology. 1998;8:285–95. [PubMed] [Google Scholar]

  3. Falcone G, Nickerson WJ. Cell-wall mannan-protein of baker’s yeast. Science. 1956;124:272–3. [PubMed] [Google Scholar]

So the mannose is actually coming from the candida yeast infection being studied by Monson & Wilkinson (1981).

Sharma et al. also points out that mannose has good, bad or ugly outcomes depending on its steady state levels and metabolic flux and their review describes the role of mannose at cellular level and its impact on organisms.

Mannose is a simple sugar with a complex life. It’s a welcome therapy for genetic and acquired human diseases, but it kills honeybees and blinds baby mice. It could cause diabetic complications. Mannose chemistry, metabolism, and metabolomics in cells, tissues and mammals can help explain these multiple systemic effects.

References

Monson, T. P., & Wilkinson, K. P. (1981). Mannose in body fluids as an indicator of invasive candidiasis. Journal of clinical microbiology, 14(5), 557–562. https://doi.org/10.1128/jcm.14.5.557-562.1981 (Open access at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC273987/)

Sharma, V., Ichikawa, M., & Freeze, H. H. (2014). Mannose metabolism: more than meets the eye. Biochemical and biophysical research communications, 453(2), 220-228. https://doi.org/10.1016/j.bbrc.2014.06.021 (Open access at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4252654/)

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TLDR: yeast (C. albicans) cell walls have a "hairy" abundance of mannan as the outer layer, which is a polymer of mannose.

Also of some note, there's an innate part of the human immune system (MBL) that detect and attacks these...

Frankly detecting mannose as a yeast infection indicator seems a proposal that never really took off in clinical practice as detecting mannan and/or its antibodies is fairly practical and subject to fewer confounders. (You may want for instance to detect galactomannan for differential diagnosis from aspergillosis, etc.)

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