This project was extended in FY 2014 to further analyze the patterns of inflammasome-generated cytokine production by RPE, microglia and myeloid cells. Human fetal RPE (hfRPE) and the cell line ARPE-19 exhibited in general a similar pattern of cytokine production, but the hfRPE cells demonstrated more restrictive RPE-specific features. Thus, both cell populations produced constitutively considerable levels of IL-18, but only ARPE-19 cells also produced measurable amounts of IL-1beta;when primed for inflammasome generation by incubation with IL-1alpha;and LPS. We previously showed that bone marrow-derived cells, namely, microglia and the THP-1 line of monocytes/macrophages, produced remarkably higher levels of IL-1beta;than of IL-18. We expanded in FY 2014 this study concerning the pattern of preferential production of IL-1beta and IL-18, by testing purified populations of human monocytes and of macrophage populations M1 and M2. Differences were found between the patterns of response of the three cell types: when stimulated for inflammasome generation, monocyte cultures produced IL-1beta, but no IL-18, M1 macrophages produced higher levels of IL-1beta than of IL-18, whereas M2 macrophages produced higher levels of IL-18 than of IL-beta. These observations are of interest in view of macrophage M1 population, but not that of macrophage M2, having the capacity of killing bacteria. Our findings may help in learning on the functions of these cell populations in inflammatory processes in the eye. In another new portion of this study, RPE and bone marrow-derived cells were found to profoundly differ in their production pattern of IL-18 binding protein (IL-18BP). Thus, the bone marrow-derived cells produced constitutively large amounts of IL-18BP, whereas no production of this molecule could be detected in RPE cell cultures (despite their production of IL-18). These observations are of much interest in view of the biological capacity of IL-18BP: this molecule efficiently blocks the cytokine activities of IL-18. The function of IL-18 in the eye is currently a hotly debated issue. (One group Tarallo et al., Cell, 2012, 149:847 suggests that this cytokine is involved in the elimination of RPE cells during the pathogenic process of dry AMD, whereas the other group Doyle et al., Nat. Med., 2012, 18:791 provides data to show that IL-18 has anti-angiogenic properties and could provide protection against wet AMD). Our observations support the notion that IL-18 is not cytotoxic to RPE, since these cells express IL-18 constitutively and it is unreasonable to assume that these cells are targets for the cytotoxic activity of the cytokine they produce. Furthermore, RPE cells are the only known cells that express IL-18 but no IL-18BP, thus allowing IL-18 to function at its fullest capacity in the eye. In contrast to RPE cells, bone marrow-derived cells produce high levels of IL-18BP, a molecule that efficiently blocks the biological activity of IL-18. Our data thus shed new light on the involvement of cytokines in the pathogenic process of AMD.
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| Shi, Guangpu; Chen, Siqi; Wandu, Wambui S et al. (2015) Inflammasomes Induced by 7-Ketocholesterol and Other Stimuli in RPE and in Bone Marrow-Derived Cells Differ Markedly in Their Production of IL-1? and IL-18. Invest Ophthalmol Vis Sci 56:1658-64 |
| Zhao, Chan; Shi, Guangpu; Vistica, Barbara P et al. (2014) Induced regulatory T-cells (iTregs) generated by activation with anti-CD3/CD28 antibodies differ from those generated by the physiological-like activation with antigen/APC. Cell Immunol 290:179-84 |
