Lipopolysaccharide preconditioning increased the level of regulatory B cells in the spleen after acute ischaemia/reperfusion in mice

Abstract

Background: The inflammatory reaction of the spleen is an important component in the pathophysiology of cerebral ischaemia (CI). Regulatory B cells (Bregs) derived from the spleen can inhibit the expansion of inflammation and reduce the damage caused by CI.

Aim: The aim of the present study was to explore changes in spleen function and Bregs production due to lipopolysaccharide preconditioning (LPS PC) in ischaemia/reperfusion (I/R) and to uncover potential protective effect of LPS PC on stroke.

Methods: Focal cerebral I/R mice were induced by middle cerebral artery occlusion (MCAO). Infarct size and inflammatory cell infiltration in brain tissue, athletic ability, and immune status were analysed by immunostaining, behavioural analyses, and flow cytometry, respectively.

Results: The volume of the cerebral infarct was significantly decreased in I/R mice with LPS PC (LPS + I/R) compared to I/R mice, and neuronal apoptosis was ameliorated by LPS PC. After preconditioning with LPS, locomotor activity, forelimb strength, motor endurance, motor coordination, and short-term memory were improved to varying degrees. Moreover, blood-brain barrier (BBB) dysfunction was reversed, and CD11b⁺, major histocompatibility complex-II positive (MHC-II⁺), and Gr-1⁺ cell infiltration in the brains of LPS + I/R mice was also significantly reduced. B cell-activating factor (BAFF), tumour necrosis factor alpha (TNF-α), interleukin-1 beta (IL-1β), and IL-6 in the brain and spleen in the LPS + I/R group decreased to different degrees, while the levels of transforming growth factor-β (TGF-β) and IL-10 increased. LPS PC alleviated atrophy of the spleen following I/R. In addition, the number of CD8⁺ T cells, macrophages, TNF⁺ cells, NF-κB⁺ cells, and neutrophils in the spleen was reduced, while the number of proliferating cells and CD19⁺-IL10⁺ Bregs was significantly increased. The number of follicular B (FO B) cells and marginal zone B (MZ B) cells in the spleens of LPS + I/R mice was also increased.

Conclusions: I/R mice preconditioned with LPS showed significantly reduced pathological damage, motor dysfunction, cognitive dysfunction, and inflammatory responses. LPS PC may initiate anti-inflammatory protective mechanism in the spleen after stroke, may increase the number of anti-inflammatory cells, such as Bregs, in the spleen, and may play a protective role in stroke.

Keywords: IL-10; Inflammation; Ischaemia/reperfusion; Lipopolysaccharide; Regulatory B cells; Spleen.