Blood parameters differentiate post COVID-19 condition from Myalgic Encephalomyelitis/Chronic Fatigue Syndrome and Fibromyalgia

Abstract

Post-COVID-19 condition, such as Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) and Fibromyalgia (FM), are characterized by fatigue, pain, shortness of breath, sleep disturbances, cognitive dysfunction and other symptoms, heavily impacting on patients daily functioning. Moreover, over half of patients end up fulfilling ME/CFS and/or FM clinical criteria after a few months of SARS-CoV-2 infection. Expression of the toxic human endogenous retrovirus (HERV)-W ENV protein can be induced by viral infection and HERV-W detection was correlated with acute COVID-19 severity and found significantly expressed in post-COVID-19 condition. This study shows that HERV-W ENV may also be present in prepandemic cases of ME/CFS, FM or co-diagnosed with both clinical criteria, suggesting viral participation in these chronic diseases. To learn whether associated antiviral mechanisms may also show differing patterns of immunological responses, we measured IgM, IgG, IgA and IgE antibody isotypes against SARS-CoV-2 spike and nucleocapsid antigens, the levels of IL-6, IL-8, IL-10, IFNγ and TNFα cytokines, the level of NfL, a neural damage biomarker, as well as some blood cell markers potentially related with fatigue. Importantly, some of the measured variables showed a capacity to discriminate post-COVID-19 condition cases from all other participants, with 100 % sensitivity and up to 71.9 % specificity providing a new tool for a differential diagnosis between diseases or syndromes with so many overlapping clinical symptoms. Interestingly, the detected markers showed moderate-to-strong correlations with patient symptoms pointing at novel therapeutic opportunities.

Keywords: Cytokines; Fibromyalgia; HERV-W-ENV; Immunoglobulins; Long COVID-19; Myalgic encephalomyelitis/chronic fatigue syndrome; Post COVID-19 condition; SARS-CoV-2; Serology.

Fig. 1

HERV-W envelope (ENV) expression in post-pandemic subjects (n = 193), healthy controls (HC) (n = 46); post-COVID-19 (n = 33); ME/CFS (n = 12); FM (n = 42); and co-diagnosed (n = 60). (A) for HERV-W ENV protein antigenemia are labeled in red, defined as those values above the mean+ 2SD of the background signals yielded by a panel of healthy control samples. ∗p<0.05, ∗∗p<0.01, ∗∗∗p<0.001, ∗∗∗∗p<0.0001 according to T-Test. (B) Summary table displaying number of cases expressing HERV-W-ENV (+) or with normal levels (−), ratios and percentages of HERV-W-ENV detection by study group.

Fig. 2

Anti-SARS-CoV-2 multi-isotype serology of healthy controls (n = 46), in comparison to post-COVID-19 condition (n = 33), ME/CFS (n = 12), FM (n = 42), and co-diagnosed (n = 60) cases. Levels of IgG (A), IgM (B), IgA (C) and IgE (D) against the SARS-CoV-2 nucleocapsid, spike or the combination of both (total) are shown as the mean of the area under the curve (AUC) according to electropherograms. Cut-off for each isotype was calculated as the mean of pre-pandemic controls +3 standard deviations (SD). Samples positive for HERV-W ENV protein antigenemia are labeled in red. ∗∗p < 0.01, ∗∗∗p < 0.001, ∗∗∗∗p < 0.0001 according to Mann-Whitney Test.

Fig. 3

Circulating IL-6, IL-8, IL-10, IFNγ, NFL and TNFα levels (pg/ml) in healthy controls (n = 46), in comparison to post-COVID-19 condition (n = 33), ME/CFS (n = 12), FM (n = 42), and co-diagnosed (n = 60) cases. Samples positive for HERV-W ENV protein antigenemia are labeled in red. Group differences statistical significance is indicated with ∗p < 0.05, ∗∗p < 0.01, ∗∗∗p < 0.001, ∗∗∗∗p < 0.0001 according to Mann-Whitney Test.

Fig. 4

Red blood cell analytics and platelet counts by patient study group. Post-COVID-19 condition (n = 14), ME/CFS (n = 12), FM (n = 42), and co-diagnosed (n = 60) cases. Variables are grouped in relation to red blood cells and platelets (upper) or belonging to while blood cells (lower). Units for each variable are indicated. Samples positive for HERV-W ENV protein antigenemia are labeled in red. Group differences statistical significance is indicated with ∗∗p < 0.01, ∗∗∗p < 0.001, ∗∗∗∗p < 0.0001 according to Mann-Whitney Test.

Fig. 5

Receiving Operating Characteristic (ROC) curves for post-COVID-19 condition, using Ferritin levels and Mean Corpuscular Hemoglobin Concentration (MCHC) values (A) or adding anti-SARS-CoV-2 IgE antigenemia and circulating interferon gamma (INFγ) levels (B). Area Under the Curve (AUC) values, together with Specificity and Sensitivity readings of the model are displayed.

Fig. 6

Correlations of HERV-W ENV with post-COVID-19 MHCH and INF-γ values (R>|0.5|, p ≤ 0.05, Spearman) (A), and ROC curve for post-COVID-19 condition with five variables (SARS-CoV-2 IgE antigenemia, IFN-γ, Ferritin, MCHC, and HERV-W ENV levels). Area Under the Curve (AUC) values, together with Specificity and Sensitivity readings of the model are displayed (B).

Fig. 7

Summary heatmap to represent the significance and intensity of correlations between SARS-CoV-2 IgE antigenemia, IFN-γ, Ferritin, MCHC and HERV-W ENV levels and FIQ, MFI, SF-36 and COMPASS-31questionnaire scores. Instrument subdomains are indicated. The color palette shows positive correlations in pink-red while blue displays negative correlations. R values of significant correlations (∗∗p ≤ 0.001; ∗p ≤ 0.05; and Ϯp≤0.1) are displayed.