Psychoneuroendocrinology 113 (2020) 104578 Contents lists available at ScienceDirect Psychoneuroendocrinology journal homepage: www.elsevier.com/locate/psyneuen The role of low-grade inflammation in ME/CFS (Myalgic Encephalomyelitis/ Chronic Fatigue Syndrome) - associations with symptoms T Martin A Jonsjöa,b,f,*, Gunnar L Olssona,b, Rikard K Wicksellc, Kjell Alvingd, Linda Holmströma,e, Anna Andreassonf,g a Behavior Medicine, Karolinska University Hospital, Stockholm, Sweden b Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden c Dept. of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden d Dept. of Women's and Children's Health, Uppsala University, Uppsala, Sweden e Dept. of Women's and Children's Health, Karolinska Institutet, Stockholm, Sweden f Stress Research Institute, Stockholm University, Stockholm, Sweden g Dept. of Medicine Solna, Karolinska Institutet, Stockholm, Sweden ARTICLE INFO ABSTRACT Keywords: Background: Patients with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) often present with a Myalgic encephalomyelitis range of flu-like symptoms resembling sickness behavior as well as widespread pain and concentration deficits. Chronic fatigue syndrome The aim of this study was to explore the association between inflammatory markers previously shown to be ME/CFS related to fatigue severity in ME/CFS and common ME/CFS symptoms post-exertional fatigue, impaired cog- Cytokines nitive processing, musculoskeletal pain and recurrent flu-like symptoms, and the moderating effect of sex on Symptoms these associations. Methods: 53 adult patients diagnosed with ME/CFS at a specialist clinic were included in the study. Fasting blood plasma was analyzed using the Olink Proseek Multiplex Inflammation panel (β-NGF, CCL11, CXCL1, CXCL10, IL-6, IL-7, IL-8, IL-10, IL-18, TGF-α, TGF-β-1 and SCF) and BioRad Human Cytokine Type 1 assay (TNF- α). Participants rated the average severity of symptoms (0–10) based on the 2011 International Consensus Criteria of ME/CFS during a structured clinical interview. Associations between inflammatory markers and symptom severity were analyzed using bivariate correlations and moderated regression analyses bootstrapped with 5000 repetitions. Results and conclusions: Only β-NGF was associated with the fatigue severity measure. However, higher levels of CCL11, CXCL10, IL-7, TNF-α and TGF-β-1 were significantly associated with higher levels of impaired cognitive processing and musculoskeletal pain, and sex was a significant moderator for CXCL10, IL-7 and TGF-β-1. Future studies should investigate the relationship between inflammatory markers and key symptoms in ME/CFS in a longitudinal design in order to explore if and for whom low-grade inflammation may contribute to illness de- velopment. 1. Introduction recurrent flu-like symptoms pertaining to immune activation (e.g. ma- laise, tender lymph nodes and feverishness), as well as musculoskeletal Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is pain and neurocognitive impairment (Carruthers et al., 2003). characterized by a large heterogeneity in symptoms, severity and So far, no consistent illness-specific findings have been shown in treatment response. It has been suggested that this may be due to dif- clinically used inflammatory markers, such as erythrocyte sedimenta- ferences in pathophysiological and etiological mechanisms (Aslakson tion rate or C-reactive protein. However, currently used clinical tests et al., 2009). ME/CFS is characterized by longstanding unclear fatigue may fail to detect pathophysiological processes in ME/CFS such as interfering with functioning (personal, social and work-related dis- neurological infections and inflammation (Davis and Tyler, 2005; ability) (2). Importantly, patients present with an array of additional Ghose et al., 2019) and an increasing number of studies show various ⁎ Corresponding author at: Functional Area Medical Psychology, Functional Unit Behavior Medicine, Karolinska University Hospital Solna, QA25, 171 76, Stockholm, Sweden. E-mail address: [email protected] (M.A. Jonsjö). https://doi.org/10.1016/j.psyneuen.2019.104578 Received 5 July 2019; Received in revised form 4 December 2019; Accepted 20 December 2019 0306-4530/ © 2020 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/BY-NC-ND/4.0/). M.A. Jonsjö, et al. Psychoneuroendocrinology 113 (2020) 104578 imbalances in levels of cytokines in ME/CFS, both in blood and in overnight fast. Samples were stored in room temperature before cen- cerebrospinal fluid (Hornig et al., 2016, 2015; Montoya et al., 2017; trifugation at 2000 rpm for 10 min, and was stored at -70 degrees Russell et al., 2016). In a recent study by Montoya et al., a significant Celsius until analyses. Blood plasma was analyzed using the Olink relationship between high levels of inflammatory markers and fatigue Proseek Multiplex Inflammation panel measuring 92 different analytes severity in ME/CFS was found, however more research is needed to (Olink, Uppsala, Sweden). investigate if and for whom longstanding low-grade inflammatory For this study, 13 inflammatory markers were chosen based on processes are related to symptoms in ME/CFS (Montoya et al., 2017). previous research. Three sickness behavior-related inflammatory mar- Furthermore, there is a scarcity of studies investigating the relationship kers (tumor necrosis factor (TNF)-α, interleukins (IL)-6 and (IL)-8) and between low-grade inflammation and other primary symptoms in ME/ 10 inflammatory markers previously shown to be related to fatigue CFS besides fatigue. severity in ME/CFS; IL-7, IL-10, IL-18, Eotaxin (CCL11), C-X-C motif The interaction between the immune system and the brain might chemokine (CXCL)1, CXCL10, Latency-associated peptide transforming contribute to the understanding of symptom variation in ME/CFS. In growth factor beta (LAP-TGF-β)-1, Transforming growth factor (TGF)- short, when the immune system is activated, inflammatory cytokines α, Stem cell factor (SCF) and Beta-nerve growth factor (β-NGF) were are released and soon the afflicted person will present with sickness included. The Human Cytokine Type 1 assay (BioRad, Hercules, CA, behavior such as fatigue, malaise, anxiety, anhedonia, worsened mood, USA) was used to ascertain levels of TNF-α as this marker was not reduced social interaction and increased pain sensitivity (Dantzer et al., detected in half of the samples using the Olink panel. All other markers 2008). The sickness behavior response has been considered a key me- had adequate detectability. chanism in the recovery from acute illness, while persistent sickness behavior may contribute to the debilitating symptoms in some patients 2.2.2. ME/CFS symptoms & illness duration with ME/CFS. To date, the relationships between low-grade in- Data on illness duration and symptoms were collected as part of the flammation and the commonly reported post-exertional, flu-like, mus- visit to the ME/CFS specialist clinic. A structured clinical interview with culoskeletal and neurocognitive symptoms in ME/CFS are still unclear. each participant was carried out by a senior physician. As part of the The aim of this study was to preliminarily explore the association interview, participants rated the average severity of symptoms, based between inflammatory markers and common symptoms in ME/CFS. on the 2011 International Consensus Criteria (Carruthers et al., 2011), Specifically, we wanted to investigate (a) the association between on a numerical rating scale from 0 (not present) to 10 (worst imagin- sickness behavior-related inflammatory markers and recurrent flu-like able level). Patients also reported duration of the illness, which was symptoms in ME/CFS, and (b) the associations between inflammatory cross-referenced through medical records. Symptoms were selected markers previously shown to be related to fatigue severity in ME/CFS based on (a) sickness behavior similarity (recurrent flu-like symptoms, and common ME/CFS symptoms post-exertional fatigue, impaired i.e. general malaise) and (b) previous ME/CFS research and our clinical cognitive processing and musculoskeletal pain, and (c) the moderating experience of the symptoms reported by patients as most debilitating effect of biological sex on these associations, as there is a lack of studies (post-exertional fatigue; impaired cognitive processing, i.e. slowed in ME/CFS research exploring sex differences. We also wanted to pro- thought and difficulty concentrating, and; musculoskeletal pain). vide data on inflammatory markers and symptoms as a supplement in order to enable analyses on the relationships between inflammatory 2.3. Statistical analyses markers and symptoms in ME/CFS in larger materials with data from multiple research groups and studies. All data were analyzed using SPSS version 25 (IBM Corp. IBM SPSS statistics for Macintosh, version 25. Armonk, NY: IBM Corp, 2017). 2. Methods Patient characteristics, inflammatory markers and symptoms were analyzed using descriptive statistics. Bivariate Spearman correlations 2.1. Participants and procedure were utilized for investigating (a) the association between sickness behavior-related inflammatory markers (TNF-α, IL-6 and IL-8) and re- 53 adult patients diagnosed with ME/CFS were included in the current flu-like symptoms and; (b) the association between in- study. Participants were recruited consecutively as part of the diag- flammatory markers implicated in ME/CFS (IL-7, IL-10, IL-18, CCL11, nostic