Levels of IL-6 in peripheral blood and cerebrospinal fluid of Alzheimer's disease: a meta-analysis

Abstract

BACKGROUND: Alzheimer's disease (AD) is a common degenerative disease of the central nervous system in the elderly. Several reports have described the serum levels of interleukin (IL-6) in AD. In order to elucidate the status of IL-6 in AD, the article conducted a meta-analysis of previously published results to assess the levels of IL-6 from different tissue sources in AD. METHODS: The levels of Th17 related cytokines (IL-6) in peripheral blood or cerebrospinal fluid (CSF) of AD were systematically reported in domestic and foreign databases. The article assessed pooled data using a random-effects model.The I-square index (I2) was used to assess inconsistency and publication bias was assessed by examining funnel plot asymmetry using the Begg and Egger test. Results: Among 1348 identified studies, the article selected 45 studies for analysis, 36 to investigate IL-6 levels in peripheral blood and 9 to investigate IL-6 levels in CSF of AD versus healthy controls (HCs). The analysis revealed that IL-6 content in peripheral blood of AD was significantly higher than that of HCs[SMD = 0.913, 95% CI (0.345, 1.481), P < 0.05], while the level of IL-6 in CSF showed no statistical significance [SMD = 0.132, 95% CI (-0.579, 0.843), P > 0.05] and could not be used as a marker in AD. CONCLUSIONS: In AD, the level of IL-6, a relevant marker, is increased, and spontaneous IL-6 production by peripheral blood mononuclear cells may be a marker of future AD risk in the elderly, and these data strengthen evidence of the pathophysiological role of inflammation in the development of clinical AD, but suggest that the mechanism of IL-6 action still needs more research and can be used as a potential target to address the problem of AD in the future.