Immune activation and immune-associated neurotoxicity in Long-COVID: A systematic review and meta-analysis of 82 studies comprising 58 cytokines/chemokines/growth factors.

Background: Multiple studies have shown that Long COVID (LC) disease is associated with heightened immune activation, as evidenced by elevated levels of inflammatory mediators. However, there is no comprehensive meta-analysis focusing on activation of the immune inflammatory response system (IRS) and the compensatory immunoregulatory system (CIRS) along with other immune phenotypes in LC patients. Objectives: This meta-analysis is designed to explore the IRS and CIRS profiles in LC patients, the individual cytokines, chemokines, growth factors, along with C-reactive protein (CRP) and immune-associated neurotoxicity. Methods: To gather relevant studies for our research, we conducted a thorough search using databases such as PubMed, Google Scholar, and SciFinder, covering all available literature up to December 20th, 2023. Results: The current meta-analysis encompassed 82 studies that examined multiple immune profiles, C-reactive protein, and 58 cytokines/chemokines/growth factors in 3836 LC patients versus 4537 normal controls (NC). LC patients showed significant increases in IRS/CIRS ratio (standardized mean difference (SMD:0.156, confidence interval (CI): 0.051;0.261), IRS (SMD: 0.345, CI: 0.222;0.468), M1 macrophage (SMD: 0.421, CI: 0.290;0.551), T helper (Th)1 (SMD: 0.353, CI: 0.189;0.517), Th17 (SMD: 0.492, CI: 0.332;0.651) and immune-associated neurotoxicity (SMD: 0.327 CI: 0.205;0.448). In addition, CRP and 19 different cytokines displayed significantly elevated levels in LC patients compared to NC. Conclusion: LC disease is characterized by IRS activation and increased immune-associated neurotoxicity. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement The study was funded by the C2F program, Chulalongkorn University, Thailand, No. 64.310/436/2565 to AFA, an FF66 grant and a Sompoch Endowment Fund (Faculty of Medicine), MDCU (RA66/016) to MM, and Grant № BGRRP2.0040007С01 Strategic Research and Innovation Program for the Development of MU PLOVDIV(SRIPDMUP), Creation of a network of research higher schools, National plan for recovery and sustainability, European Union NextGenerationEU. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes Upon full utilization by all authors, the last author, MM, will address legitimate inquiries for the dataset used in this meta-analysis, which will be shared in an Excel file format.