Petrov, Steliyan, Bozhkova, Martina, Ivanovska, Mariya et al. · International journal of molecular sciences · 2026 · DOI
Researchers compared immune cell patterns in 103 people with ME/CFS, 63 with long COVID, and 41 healthy controls using blood tests. They observed that ME/CFS and long COVID show different patterns of immune cell activity—long COVID appeared to show persistent immune activation, while ME/CFS appeared associated with reduced immune signalling. These are early findings from one study and do not yet tell us what causes either condition or how to treat it.
By analogy with long COVID, this study suggests ME/CFS may involve a distinct immune signature—specifically, reduced costimulatory signalling and impaired immune cell trafficking—that differs from the persistent activation seen in long COVID. If these patterns are confirmed in larger samples, they could help distinguish ME/CFS from other post-infectious conditions and eventually guide disease-specific diagnostic approaches. The relevance of these immune signatures to ME/CFS pathophysiology remains to be established in dedicated ME/CFS cohorts.
This study does not establish that observed immune differences cause ME/CFS symptoms or functional impairment. It does not prove these immune signatures are specific to ME/CFS or stable over time. The cross-sectional design cannot determine whether immune cell changes precede, accompany, or result from illness. It does not provide evidence that targeting these immune patterns would treat ME/CFS.
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 →
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Primary citation
Petrov, Steliyan, Bozhkova, Martina, Ivanovska, Mariya, Kalfova, Teodora, Dudova, Dobrina, Todorova, Yana, et al. (2026). Comprehensive Immunophenotyping of Monocytes and Dendritic Cells Suggests Distinct Pathophysiology in Chronic Fatigue Syndrome and Long COVID.. International journal of molecular sciences. https://doi.org/10.3390/ijms27104488
BibTeX
@article{mecfsatlas-petrov-2026-comprehensive-immunophenotyping,
author = {Petrov, Steliyan and Bozhkova, Martina and Ivanovska, Mariya and Kalfova, Teodora and Dudova, Dobrina and Todorova, Yana and Dimitrova, Radostina and Murdjeva, Marianna and Taskov, Hristo and Nikolova, Maria and Maes, Michael},
title = {Comprehensive Immunophenotyping of Monocytes and Dendritic Cells Suggests Distinct Pathophysiology in Chronic Fatigue Syndrome and Long COVID.},
journal = {International journal of molecular sciences},
year = {2026},
doi = {10.3390/ijms27104488},
note = {PubMed: 42196466},
url = {https://www.mecfsatlas.com/evidence/petrov-2026-comprehensive-immunophenotyping},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-28. https://www.mecfsatlas.com/evidence/petrov-2026-comprehensive-immunophenotyping
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