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.