Novel cytokines in innate immunity: IL-27 and IL-30 enhance responsiveness to gram-negative bacterial components in human myeloid cells

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Authors
Petes, Carly
Keyword
Interleukin-27 , Lipopolysaccharide , Innate immunity , Myeloid cells , Gram-negative bacteria , Interleukin-30
Abstract
In response to microbial stimuli, innate myeloid cells are potent producers of cytokines that function to mediate inflammation. This thesis investigates two related cytokines, IL-27 and IL-30, to identify novel proinflammatory mechanisms to improve treatments for bacterial infections. IL-27 is comprised of IL-27p28 and EBI3 subunits; the IL-27p28 subunit, also named IL-30, can also signal independently of EBI3. To date, most studies on IL-27 have focused on its role in CD4+ T cell differentiation. IL-30 has been recognized as an antagonist of IL-6, IL-11, and IL-27 in CD4+ T cells. In primary monocytes, IL-27 promotes proinflammatory cytokine production and TLR4 expression in monocytes for a potent inflammatory response to bacterial endotoxin, LPS. Barring these studies, functions of IL-27 and IL-30 in human myeloid cells have not been well described, and therefore are the focus of this thesis. Specifically, this thesis compares IL-27 and IL-30 signaling in human monocytes and explores novel proinflammatory effects of IL-27 and IL-30 on cytokine production in response to either Gram-negative bacteria or bacterial components in myeloid cells. The effects of IL-27 are explored in Salmonella enterica infection, NLRP3 inflammasome activation, and induction of endotoxin (LPS) tolerance in human monocytes and macrophages, while the effects of IL-30 are defined in human monocytes. IL-27 and IL-30 induce IP-10 production in human monocytes in a STAT-dependent manner. Furthermore, pre-treatment with IL-6 interferes with IL-27 and IL-30 functions in human monocytes. Similarly to TLR4, IL-27 treatment also enhances TLR5 expression in human monocytes and macrophages, inducing cytokine production in response to TLR agonists LPS and flagellin or S. enterica infection. IL-27 also increases LPS/ATP-mediated NLRP3 inflammasome activation and IL-1β production in human monocytes via upregulated TLR4 and P2X7 expression. Comparing human THP-1 monocytes and PMA-differentiated THP-1 macrophages, CD14 expression plays a role in LPS and IL-27 responsiveness, whereby IL-27-mediated inhibition of LPS tolerance is greater in CD14low THP-1 monocytes compared to CD14high PMA-differentiated THP-1 macrophages. Overall, this thesis demonstrates novel proinflammatory roles for IL-27 and its subunit IL-30 in innate immune responses and may serve as novel adjuvant candidates for vaccine design against Gram-negative bacterial infections.
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