Abstract
Chronic inflammation is thought to promote tumorigenesis and metastasis by several mechanisms, such as affecting tumor cells directly, establishing a tumor-supporting microenvironment, enhancing tumor angiogenesis, and suppressing antitumor immunity. In this review, we discuss the recent advances in our understanding of how inflammation induces the immunosuppressive tumor microenvironment, such as increasing the level of pro-inflammatory cytokines, chemokines, and immunosuppressive molecules, inducing immune checkpoint molecules and cytotoxic T-cell exhaustion, and accumulating regulatory T (Treg) cells and myeloid-derived suppressor cells (MDSCs). The suppression of antitumor immunity by inflammation is especially examined in the liver and colorectal cancer. In addition, chronic inflammation is induced during aging and causes age-related diseases, including cancer, by affecting immunity. Therefore, we also discuss the age-related diseases regulated by inflammation, especially in the liver and colon.
Highlights
Inflammation is divided into two types by duration, acute inflammation, and chronic inflammation
Growth factors and pro-inflammatory cytokines induced by chronic inflammation directly enhance cancer cell proliferation, suppress cell death, and induce angiogenesis
IL-6, and IL-17 produced by IL-17-producing cells, directly promote the proliferation and pro-inflammatory cytokines produced at high levels in human colorectal cancer (CRC); they mainly actisurvival of adenoma cells via the activation of NF-κB and STAT3 [70,71]
Summary
Inflammation is divided into two types by duration, acute inflammation, and chronic inflammation. Acute inflammation is considered beneficial because of its roles in eliminating pathogens and necrotic cells and inducing tissue regeneration and repair [1]. Immunosuppression occurs after tissue repair or the elimination of pathogens and necrotic cells to resolve inflammation. In chronic inflammation, immunosuppression permanently persists due to the lack of the normal negative feedback mechanism. Prostaglandins, essential in inducing inflammatory responses, are critical mediators in establishing the immunosuppressive microenvironment. Chronic inflammation is closely related to aging and promotes age-related diseases by affecting immunity. We will discuss the recent advances in the research on how inflammation affects antitumor immunity and causes age-related diseases, especially in the liver and colon
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