IL-2 and TCR stimulation induce expression and secretion of IL-32ß by human T cells.

IL-32 expression is important for pathogen clearance but detrimental in chronic inflammation, autoimmunity, and cancer. T cells are major IL-32 producers in these diseases and key mediators of pathogen and tumor elimination but also autoimmune destruction. However, their contribution to IL-32 biology during immune responses is hardly understood due to several isoforms with divergent inflammatory properties. Here, we identified IL-32ß as the predominant isoform in various T cell subsets of healthy individuals and breast cancer patients with the highest levels detected in intratumoral regulatory T cells. We show that IL-32ß is induced by IL-2 but IL-32ß release requires T Cell Receptor rather than IL2R stimulation. Using inhibitors of protein secretion pathways and serial (ultra)centrifugation of T cell supernatants, we demonstrate that T cells actively secrete IL-32ß unconventionally, as a free protein and, to a minor degree, through exosomes. Thus, our data identify activated T cells as major IL-32ß secretors in health and cancer.

Enhanced neuroinflammatory responses after systemic LPS injection in IL-32ß transgenic mice.

IL-32 is a proinflammatory cytokine, and involved in various diseases including infection, inflammation, and cancer. However, effects of IL-32 on neuroinflammation remain obscure. Herein, we examined the effects of IL-32ß on systemic LPS-induced neuroinflammation using IL-32ß transgenic (Tg) mice. IL-32ß wild type (WT) and Tg mice received LPS injection (5 mg/kg, i.p.), and then neuroinflammatory responses were evaluated. Systemic LPS caused remarkable gliosis in the brain at 12 h regardless of genotypes. The gliosis in WT mice was sustained by 24 h, whereas it became more severe in Tg mice by 24 h. Proinflammatory cytokines and proteins were increased at 12 h both in WT and Tg brains. The elevated levels of TNFα and VCAM-1were not altered over time, while levels of IL-6, IL-1ß and iNOS were dropped in WT mice. In contrast, elevated levels IL-6, IL-1ß, iNOS and VCAM-1 were sustained, and level of TNFα was augmented in Tg brains by 24 h. Interestingly, level of IL-10 mRNA in Tg mice was remarkably higher than in WT mice at 0 h, which was decreased at 12 h and maintained by 24 h. In WT brain, mRNA level of IL-10 was raised at 12 h after LPS injection, and further increased at 24 h. Activation of NF-κB signaling pathway was detected in glia cells after LPS injection which was exaggerated at 24 h in Tg mice in comparison to WT mice. These results indicate that IL-32ß enhances neuroinflammatory responses caused by systemic LPS, and this might be attributable to prolonged activation of NF-κB signaling pathway.

Decreased severity of collagen antibody and lipopolysaccharide-induced arthritis in human IL-32ß overexpressed transgenic mice.

Interleukin (IL)-32, mainly produced by T-lymphocytes, natural killer cells, epithelial cells, and blood monocytes, is dominantly known as a pro-inflammatory cytokine. However, the role of IL-32 on inflammatory disease has been doubtful according to diverse conflicting results. This study was designed to examine the role of IL-32ß on the development of collagen antibody (CAIA) and lipopolysaccharide (LPS)-induced inflammatory arthritis. Our data showed that the paw swelling volume and clinical score were significantly reduced in the CAIA and LPS-treated IL-32ß transgenic mice compared with non-transgenic mice. The populations of cytotoxic T, NK and dendritic cells was inhibited and NF-κB and STAT3 activities were significantly lowered in the CAIA and LPS-treated IL-32ß transgenic mice. The expression of pro-inflammatory proteins was prevented in the paw tissues of CAIA and LPS-treated IL-32ß transgenic mice. In addition, IL-32ß altered several cytokine levels in the blood, spleen and paw joint. Our data indicates that IL-32ß comprehensively inhibits the inflammation responses in the CAIA and LPS-induced inflammatory arthritis model.

Interleukin-32δ interacts with IL-32ß and inhibits IL-32ß-mediated IL-10 production.

There is growing evidence for multifunctional properties of IL-32. We previously demonstrated that IL-32ß upregulates IL-10 production through the association with PKCδ. In this study, we examined the effects of other IL-32 isoforms on IL-10 production. We found that IL-32δ decreased IL-10 production and investigated the inhibitory mechanism of IL-32δ. We showed that IL-32δ suppressed IL-32ß binding to PKCδ by interacting with IL-32ß. The inhibitory effect of IL-32δ on IL-32ß association with PKCδ was further verified by immuno-fluorescence staining. The co-localization of IL-32ß and PKCδ around the nuclear membrane was disrupted by IL-32δ. Our data therefore indicate that IL-32δ plays an inhibitory role against IL-32ß function, which also suggests that IL-32 may be regulated by its own isoform.