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

Abstract 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.