Increased expression of T cell immunoglobulin and mucin domain 3 aggravates brain inflammation via regulation of the function of microglia/macrophages after intracerebral hemorrhage in mice

Background: Microglia/macrophages are known to play important roles in initiating brain inflammation after spontaneous intracerebral hemorrhage (ICH). T cell immunoglobulin and mucin domain-3 (Tim-3) have been proven to play a critical part in several inflammatory diseases through regulation of both adaptive and innate immune responses. Tim-3 can be expressed by microglia/macrophages and regulates their function in the innate immune response. However, the effect of Tim-3 on inflammatory responses following ICH is unclear. Methods: In this study, we investigated Tim-3 expression, the inflammatory cytokines tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta), and brain water content in peri-hematomal brain tissue at 12 hours and at 1, 3, 5, and 7 days post-ICH in wild type (WT) ICH and Tim-3(-/-) ICH mice. The numbers of Tim-3 positive cells, astrocytes, neutrophils and microglia/macrophages were detected using immunofluorescence staining. Cytokines were measured by ELISA. Double immunoflurorescence labeling was performed to identify the cellular source of Tim-3 expression. Mouse neurological deficit scores were assessed through animal behavior. Results: Expression of Tim-3 increased early in mouse peri-hematomal brain tissue after autologous blood injection, peaked at day 1, and was positively correlated with the concentrations of TNF-alpha, IL-1 beta, and brain water content. Tim-3 was predominantly expressed in microglia/macrophages. Compared with WT mice, Tim-3(-/-) mice had reduced ICH-induced brain inflammation with decreased TNF-alpha and IL-1 beta, cerebral edema and neurological deficit scores. Moreover, Tim(-/-) inhibited activation of microglia/macrophages. The number of activated microglia/macrophages in Tim-3(-/-) ICH mice was much lower than that in WT ICH mice. Conclusions: Our findings demonstrate that Tim-3 plays an important role in brain inflammation after ICH, and may be a potential treatment target.