Landay, A L, Jessop, C, Lennette, E T et al. · Lancet (London, England) · 1991 · DOI
Researchers used specialized tests to examine immune cells from 147 people with ME/CFS and compared them to healthy people. They found that people with ME/CFS had lower levels of certain immune cells (CD8 suppressor cells) and higher levels of immune activation markers on other immune cells. These differences were not seen in healthy people, contacts of patients, or people with other illnesses, suggesting that immune system activation may be involved in ME/CFS.
This study provided early evidence that immune activation, rather than persistent viral infection, may characterize ME/CFS in many patients. These findings helped establish immune dysregulation as a legitimate biological basis for the condition, supporting patient advocacy for recognition as an organic disease and encouraging subsequent research into immunological mechanisms.
This study demonstrates an association between immune activation and ME/CFS but does not prove causation—the immune changes could be a consequence of the disease rather than its cause. The lack of viral correlation does not exclude viruses as initial triggers, as the acute viral infection may have resolved while immune activation persists. The study was also cross-sectional, so it cannot establish whether these immune markers precede symptom onset or develop as a result of chronic illness.
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
Landay, A L, Jessop, C, Lennette, E T, & Levy, J A (1991). Chronic fatigue syndrome: clinical condition associated with immune activation.. Lancet (London, England). https://doi.org/10.1016/0140-6736(91)91440-6
BibTeX
@article{mecfsatlas-landay-1991-chronic-fatigue,
author = {Landay, A L and Jessop, C and Lennette, E T and Levy, J A},
title = {Chronic fatigue syndrome: clinical condition associated with immune activation.},
journal = {Lancet (London, England)},
year = {1991},
doi = {10.1016/0140-6736(91)91440-6},
note = {PubMed: 1679864},
url = {https://www.mecfsatlas.com/evidence/landay-1991-chronic-fatigue},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-30. https://www.mecfsatlas.com/evidence/landay-1991-chronic-fatigue
Contribute
Private, reviewed by a human. Not a public comment thread.