Human Traumatic Brain Injury Induces Autoantibody Response against Glial Fibrillary Acidic Protein and Its Breakdown Products

Abstract

The role of systemic autoimmunity in human traumatic brain injury (TBI) and other forms of brain injuries is recognized but not well understood. In this study, a systematic investigation was performed to identify serum autoantibody responses to brain-specific proteins after TBI in humans. TBI autoantibodies showed predominant immunoreactivity against a cluster of bands from 38–50 kDa on human brain immunoblots, which were identified as GFAP and GFAP breakdown products. GFAP autoantibody levels increased by 7 days after injury, and were of the IgG subtype predominantly. Results from in vitro tests and rat TBI experiments also indicated that calpain was responsible for removing the amino and carboxyl termini of GFAP to yield a 38 kDa fragment. Additionally, TBI autoantibody staining co-localized with GFAP in injured rat brain and in primary rat astrocytes. These results suggest that GFAP breakdown products persist within degenerating astrocytes in the brain. Anti-GFAP autoantibody also can enter living astroglia cells in culture and its presence appears to compromise glial cell health. TBI patients showed an average 3.77 fold increase in anti-GFAP autoantibody levels from early (0–1 days) to late (7–10 days) times post injury. Changes in autoantibody levels were negatively correlated with outcome as measured by GOS-E score at 6 months, suggesting that TBI patients with greater anti-GFAP immune-responses had worse outcomes. Due to the long lasting nature of IgG, a test to detect anti-GFAP autoantibodies is likely to prolong the temporal window for assessment of brain damage in human patients.

Plasma Anti-Glial Fibrillary Acidic Protein Autoantibody Levels during the Acute and Chronic Phases of Traumatic Brain Injury: A Transforming Research and Clinical Knowledge in Traumatic Brain Injury Pilot Study

“…In parallel, we recently reported a rather unexpected immunodominant autoantibody response to GFAP and its breakdown products (BDPs) in a subset of patients with severe TBI. 26 Based on our previous anti-GFAP-autoantibody study, 26 we observed that GFAP appeared to be a dominant brain-derived autoantigen after severe TBI. We hypothesized that TBI causes protease-mediated GFAP-BDP formation in injured glial cells.…”

“…To detect and quantify AutoAb[GFAP] levels in biosamples, we used our previously published manifold autoantibody immunoblotting assay format 26 (see Supplementary Fig. 1 for assay set-up; see online supplementary material at ftp.liebertpub.com).…”

“…Because we previously identified a dominant autoantibody response to glial intermediate filament protein GFAP among patients with severe TBI, 26,[33][34][35] here we sought to expand these findings by using the TRACK-TBI pilot study cohorts and plasma samples. 1,36,37 Of 586 subjects with acute TBI from the TRACK-TBI pilot, we identified 196 with available acute plasma samples (collected within 24 h of injury) for this autoantibody study.…”

“…3,26 The distribution for AutoAb[GFAP] (mean -SE) was 2.90 -0.92 units for healthy controls, 2.97 -0.37 units for patients with acute TBI reporting no previous TBI, 8.01 -1.80 units for patients with acute TBI reporting previous TBI without LOC, and 9.11 -1.42 units for patients with acute TBI reporting previous TBI with LOC.…”

“…26,38 Here, we examined AutoAb[GFAP] levels in chronic TBI plasma samples collected from 21 subjects during rehabilitation. The demographics of these subjects are tabulated in Table 1.…”