Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating multisystem disorder characterized by immune dysregulation, metabolic impairments, neuroendocrine disturbances, endothelial dysfunction, and gastrointestinal abnormalities. Immune alterations include reduced natural killer cell cytotoxicity, T-cell exhaustion, abnormal B-cell subsets, and the presence of diverse autoantibodies, suggesting an autoimmune component. Gut dysbiosis and increased intestinal permeability may promote systemic inflammation and contribute to neurocognitive symptoms via the gut–brain axis. Neuroendocrine findings such as hypothalamic–pituitary–adrenal (HPA) axis hypofunction and altered thyroid hormone metabolism further compound metabolic and immune abnormalities. Metabolomic and mitochondrial studies identify impaired ATP generation, redox imbalance, and compensatory shifts toward alternative energy pathways underlying hallmark symptoms like post-exertional malaise. Endothelial dysfunction driven by oxidative and nitrosative stress, along with autoantibody-mediated receptor interference, may explain orthostatic intolerance and impaired perfusion. Collectively, ME/CFS appears to arise from a self-sustaining cycle of chronic inflammation, metabolic insufficiency, and neuroimmune imbalance.

Background: Understanding the duration and quality of immune memory following SARS-CoV-2 infection and vaccination is critical for informing public health strategies and vaccine development. While waning antibody levels have raised concerns about long-term protection, the persistence of memory B cells (MBCs) and T cells plays a vital role in sustaining immunity. Materials and Methods: We conducted a longitudinal prospective study over 12 months, enrolling 285 participants in total, either after natural infection or vaccination with BNT162b2 or mRNA-1273. Peripheral blood samples were collected at four defined time points (baseline, 1–2 months, 6–7 months, and 12–13 months after vaccination or disease onset). Immune responses were assessed through serological assays quantifying anti-RBD IgG and neutralizing antibodies, B-ELISPOT, and multiparameter flow cytometry for S1-specific memory B cells. Results: Both mRNA vaccines induced robust B cell and antibody responses, exceeding those observed after natural infection. Memory B cell frequencies peaked at 6 months and declined by 12 months, but remained above the baseline. The mRNA-1273 vaccine elicited stronger and more durable humoral and memory B-cell-mediated immunity compared to BNT162b2, likely influenced by its higher mRNA dose and longer prime-boost interval. Class-switched memory B cells and S1-specific B cells were significantly expanded in vaccine recipients. Natural infection induced more heterogeneous immune memory. Conclusions: Both mRNA vaccination and natural SARS-CoV-2 infection induce a comparable expansion of memory B cell subsets, reflecting a consistent pattern of humoral immune responses across all studied groups. These findings highlight the importance of vaccination in generating sustained immunological memory and suggest that the vaccine platform and dosage influence the magnitude and durability of immune responses against SARS-CoV-2.

Background: Chronic Fatigue Syndrome (CFS), also known as Myalgic Encephalomyelitis (ME), is a debilitating condition characterized by persistent fatigue and multisystemic symptoms, such as cognitive impairment, musculoskeletal pain, and post-exertional malaise. Recently, parallels have been drawn between ME/CFS and Long COVID, a post-viral syndrome following infection with SARS-CoV-2, which shares many clinical features with CFS. Both conditions involve chronic immune activation, raising questions about their immunopathological overlap. Objectives: This study aimed to compare immune biomarkers between patients with ME/CFS or Long COVID and healthy controls to explore shared immune dysfunction. Methods: We analyzed lymphocyte subsets, cytokine profiles, psychological status and their correlations in 190 participants, 65 with CFS, 54 with Long COVID, and 70 healthy controls. Results: When compared to healthy subjects, results in both conditions were marked by lower levels of lymphocytes (CFS—2.472 × 10⁹/L, p = 0.006, LC—2.051 × 10⁹/L, p = 0.009), CD8⁺ T cells (CFS—0.394 × 10⁹/L, p = 0.001, LC—0.404 × 10⁹/L, p = 0.001), and NK cells (CFS—0.205 × 10⁹/L, p = 0.001, LC—0.180 × 10⁹/L, p = 0.001), and higher levels of proinflammatory cytokines such as IL-6 (CFS—3.35 pg/mL, p = 0.050 LC—4.04 pg/mL, p = 0.001), TNF (CFS—2.64 pg/mL, p = 0.023, LC—2.50 pg/mL, p = 0.025), IL-4 (CFS—3.72 pg/mL, p = 0.041, LC—3.45 pg/mL, p = 0.048), and IL-10 (CFS—2.29 pg/mL, p = 0.039, LC—2.25 pg/mL, p = 0.018). Conclusions: Notably, there were no significant differences between CFS and Long COVID patients in the tested biomarkers. These results demonstrate that ME/CFS and Long COVID display comparable immune and inflammatory profiles, with no significant biomarker differences observed between the two groups.

Measurable Residual Disease (MRD) assessment in pediatric acute lymphoblastic leukemia (ALL) is crucial for relapse prediction and treatment guidance. Multiparameter flow cytometry (MFC) enhances detection but faces limitations due to insufficient leukemia-associated immunophenotypes (LAIPs) and antigen modulation. This study explores new markers to improve MFC-based MRD detection in B-cell precursor ALL (BCP-ALL). Expression-patterns of seven aberrancy markers, i.e., CD44, CD304, CD73, CD86, CD123, CD99, CD58, and one B-cell maturation marker, CD22, were studied in 143 samples with leukemic-blasts from sixty-one childhood BCP-ALL patients and in hematogones of 20 non-leukemic bone marrow (BM) samples using fourteen-color MFC. The highest relative frequences of LAIPs amounted to 82.50%, reported for CD99 and CD58, followed by CD44 (81.10%), CD73 (76.20%), CD22 (73.40%), CD304 and CD86 (68.50%), while the lowest relative frequence was CD123 (44.40%). Differential expression of CD58, CD304, and CD73 in diagnostic samples was highly significant (p < 0.01) between pre-B-I, pre-B-II, immature B cells, and BCP-ALL blasts. In MRD-positive samples CD73 showed significantly high (p < 0.01) differential expression between all stages of hematogones and residual blasts, followed by CD304, CD58, and CD22. CD73 and CD304 were identified as the most reliable among the tested markers for distinguishing both diagnostic and MRD blasts from normal B cell precursors.

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and long Coronavirus Disease 2019 (long COVID) are complex chronic conditions that often follow infectious triggers with overlapping clinical features but poorly defined pathophysiological relationships. This study aimed to identify disease-specific immune signatures through multiparameter immunophenotyping of monocytes, dendritic cells, and T cell subsets. A total of 207 participants were included (ME/CFS: n = 103; long COVID: n = 63; healthy controls: n = 41). Peripheral blood mononuclear cells were analyzed using multiparameter flow cytometry. Statistical analyses included non-parametric testing, age-adjusted Analysis of covariance (ANCOVA), correlation network analysis, and principal component analysis (PCA). Long COVID was characterized by increased M2-like monocyte polarization, elevated CD80 expression across monocyte subsets, expansion of dendritic cells, and reduced expression of activation markers, indicating persistent immune activation with features of immune exhaustion. In contrast, ME/CFS exhibited reduced costimulatory molecule expression, impaired C-C chemokine receptor type 7 (CCR7)-mediated immune cell trafficking, and less coordinated activation patterns, consistent with a state of immune suppression. Correlation network analysis revealed more extensive and integrated immune interactions in long COVID, while PCA identified distinct immunophenotypic components and enabled moderate discrimination between the two conditions. These findings demonstrate that ME/CFS and long COVID are characterized by distinct immune profiles, supporting the concept of divergent immunopathological mechanisms. The identified signatures may contribute to biomarker development and guide targeted therapeutic approaches.

Chronic immune dysregulation is the possible pathophysiological mechanism in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and long coronavirus infectious disease (long COVID, LC). However, a detailed characterization of regulatory and effector T-cell subsets in these conditions remains limited. To assess and compare T-cell subsets in relation to serum biomarkers of chronic activation and oxidative/nitrosative stress in an attempt to differentiate between LC and ME/CFS patients. Peripheral blood mononuclear cells (PMNC) from LC patients (n = 89), ME/CFS patients (n = 125), and healthy controls (HC, n = 80) were analyzed using multiparameter flow cytometry. The frequencies of naïve (CD45RA+), effector (CD45RA-), CD31+, CD39+, CD73+, GARP+, PI16+, CD15s/CD161+, and CD147+ Treg subsets were determined in relation to CD4+ and CD8+ T-cell differentiation, activation, and effector subsets. Catalase (CAT), superoxide dismutase 1 (SOD1), glutathione peroxidase 1 (GPX1), malondialdehyde (MDA), nitric oxide synthase 1 and 3 (NOS1, NOS3), zonulin, lipopolysaccharide (LPS), immunoglobulin G (IgG) against lipopolysaccharide (IgG-LPS), Toll-like receptor 4 (TLR4), indoleamine 2,3-dioxygenase (IDO), and Dickkopf-related protein 1 (DKK1) were measured in serum by ELISA. Clinical symptom scores (HAMA, HAMD, FF, dePol) were additionally assessed. The immune-serum biomarkers distinguishing LC, ME/CFS, and HC comprised Th17, CD15s+CD161−eTreg, and CD161+ Treg. The five-marker signature retained significance after adjustment for age, BMI, and sex. Altered T-cell subsets were strongly associated with markers of oxidative (GPX1) and nitrosative (NOS3) stress but not directly with symptom severity. ME/CFS showed a strong separation from HC across Random Forest (AUC = 0.907) and logistic regression (AUC = 0.924). The modest distinction of LC from HC (AUC = 0.727 and 0.577 respectively) possibly reflected important endotypic diversity, though differences in disease duration, vaccination history, biomarker selection, and other cohort characteristics might add to it. MDA was an independent predictor for three-class classification, ME/CFS vs. HC, and LC vs. HC pairwise comparisons, while GPX1 discriminated between ME/CFS and LC. In spite of shared biomarkers of oxidative stress and T-cell response dysregulation, our results support the hypothesis that LC and ME/CFS differ in the extent of cellular damage and the exhaustion of compensatory mechanisms.