Natelson, B H, Denny, T, Zhou, X D et al. · Journal of affective disorders · 1999 · DOI
Researchers tested whether depression and ME/CFS are caused by an overactive immune system. They compared immune cell counts and immune signaling molecules in people with depression, people with ME/CFS who later developed depression, and healthy controls. Surprisingly, they found no signs of immune activation in either patient group—instead, the data suggested the immune system was actually downregulated (less active) in people with depression.
This study challenges a widely-held hypothesis that depression involves immune activation, which has important implications for understanding ME/CFS pathophysiology. Since some patients with ME/CFS develop depression, understanding whether depression itself involves immune dysfunction—and how this relates to ME/CFS immune abnormalities—helps clarify whether these are overlapping conditions or distinct entities.
This study does not establish that immune function is normal in depression or ME/CFS—it only shows immune activation is not required. The cross-sectional design cannot prove causation or temporal relationships. Medication use in some subjects could mask immune changes, and findings from 1999 may not capture more sensitive modern immune measurements.
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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