Nijs, J, Van Oosterwijck, J, Meeus, M et al. · Journal of internal medicine · 2010 · DOI
This study looked at what happens in the blood after people with ME/CFS exercise. Researchers compared 22 women with ME/CFS to 22 healthy women and measured specific immune markers (elastase, IL-1beta, and complement C4a) before and after two different types of exercise. Both types of exercise triggered postexertional malaise (a worsening of symptoms after activity) in the ME/CFS group, but surprisingly, the immune markers they measured didn't show significant changes in either group.
This research directly investigates the biological mechanisms behind postexertional malaise, a hallmark symptom affecting up to 95% of ME/CFS patients. Understanding what triggers PEM at the molecular level is crucial for developing treatments and validating diagnostic biomarkers. The findings suggest that the immune response in ME/CFS may be more complex than these three markers alone, prompting further investigation into PEM mechanisms.
This study does not prove that elastase, IL-1beta, and complement C4a are not involved in PEM—it only shows they did not change acutely after single exercise bouts. The study cannot determine causation or definitively rule out these biomarkers, as measurements may need to occur at different timepoints or in other biological compartments. A negative finding in acute circulating levels does not exclude their role in PEM pathophysiology.
About the PEM badge: “PEM required” means post-exertional malaise was an explicit required diagnostic criterion for participant inclusion in this study — not that PEM was studied, observed, or discussed. Studies using criteria that do not require PEM (e.g. Fukuda, Oxford) are tagged “PEM not required”. How the atlas works →
The first block is for the primary paper and is the citation you should use in research work. The atlas-snapshot line only applies if you are specifically referring to this atlas’s reading of the paper on the date shown.
Primary citation
Nijs, J, Van Oosterwijck, J, Meeus, M, Lambrecht, L, Metzger, K, Frémont, M, et al. (2010). Unravelling the nature of postexertional malaise in myalgic encephalomyelitis/chronic fatigue syndrome: the role of elastase, complement C4a and interleukin-1beta.. Journal of internal medicine. https://doi.org/10.1111/j.1365-2796.2009.02178.x
BibTeX
@article{mecfsatlas-nijs-2010-unravelling-nature,
author = {Nijs, J and Van Oosterwijck, J and Meeus, M and Lambrecht, L and Metzger, K and Frémont, M and Paul, L},
title = {Unravelling the nature of postexertional malaise in myalgic encephalomyelitis/chronic fatigue syndrome: the role of elastase, complement C4a and interleukin-1beta.},
journal = {Journal of internal medicine},
year = {2010},
doi = {10.1111/j.1365-2796.2009.02178.x},
note = {PubMed: 20433584},
url = {https://www.mecfsatlas.com/evidence/nijs-2010-unravelling-nature},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-25. https://www.mecfsatlas.com/evidence/nijs-2010-unravelling-nature
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