The Role of Acute Neuroinflammation in Patient Recovery Post-Traumatic Brain Injury: A Literature Review

Abstract

Traumatic brain injury (TBI) is a leading cause of death and disability worldwide, affecting millions annually. Acute neuroinflammation following traumatic brain injury (TBI) is an essential process for tissue repair and recovery. However, excessive, or prolonged inflammation can exacerbate damage, contributing to secondary brain injury. This review aims to consolidate the complex balance between beneficial and harmful inflammatory responses in TBI, exploring how this balance impacts patient outcomes. This review synthesizes findings from recent studies examining neuroinflammatory biomarkers during the first two weeks post-injury. A systematic search of PubMed, Nature, and related databases identified studies reporting cytokines, chemokines, cell activation markers, acute phase proteins, and oxidative stress indicators in the brain following closed-head TBI. After applying strict inclusion and exclusion criteria, ten studies were selected. These formed the basis for evaluating temporal patterns of inflammation and identifying biomarkers linked to secondary injury and recovery to understand the boundary between beneficial and harmful responses. Proinflammatory cytokines including interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), interleukin-8 (IL-8), and monocyte chemoattractant protein-1 (MCP-1), consistently rose within hours of injury and remained elevated for several days, with IL-6 and IL-8 often exceeding 1000 pg/mL – levels more than 100-fold above baseline, indicating severe immune activation and potential contribution to secondary injury. The anti-inflammatory mediators interleukin-10 (IL-10) and interleukin-1 receptor antagonist (IL-1ra) also increased, but to a lesser degree. Markers of immune activation, such as cluster of differentiation 68 (CD68) and soluble intercellular adhesion molecule-1 (sICAM-1)) were elevated in brain tissue and cerebrospinal fluid (CSF). Biomarkers of axonal and neuronal injury, including neurofilament light chain (NFL) and ubiquitin carboxy-terminal hydrolase L1(UCH-L1),were significantly elevated within 24–72 hours. Neuroinflammation in TBI involves overlapping immune responses that vary with time, location, and severity. Cytokine activity may aid repair, but prolonged IL-6 and MCP-1 elevation can worsen damage. The complexity of immune activation and structural injury suggests that no single biomarker is sufficient. Multi-marker models may offer better tools to guide treatment. This review seeks to inform future approaches and support the development of targeted strategies for regulating inflammation in TBI.