Description: Chronic graft-versus-host disease (GVHD) is a major cause of late death and morbidity after allogeneic hematopoietic cell transplantation, but its pathogenesis remains unclear. We investigated the role of the programmed death-1 (PD-1) pathway in chronic GVHD using a well-defined mouse model of B10.D2 (H-2 d ) donor to BALB/c (H-2 d ) recipients. PD-1 expression on allogeneic donor T cells was upregulated continuously in chronic GVHD development, whereas PD-L1 expression in host tissues was transiently upregulated and declined to basal levels in the late posttransplant period. Blockade of the PD-1 pathway by anti–PD-1, anti–PD-L1, or anti–PD-L2 mAbs exacerbated clinical and pathologic chronic GVHD. Chimeric mice revealed that PD-L1 expression in host tissues suppressed expansion of IL-17 + IFN- + T cells, and that PD-L1 expression on hematopoietic cells plays a role in the development of regulatory T cells only during the early transplantation period but does not affect the severity of chronic GVHD. Administration of the synthetic retinoid Am80 overcame the IL-17 + IFN- + T cell expansion caused by PD-L1 deficiency, resulting in reduced chronic GVHD damage in PD-L1 –/– recipients. Stimulation of the PD-1 pathway also alleviated chronic GVHD. These results suggest that the PD-1 pathway contributes to the suppression of Th17/Th1-mediated chronic GVHD and may represent a new target for the prevention or treatment of chronic GVHD.

Description: Chronic graft-versus-host disease (GVHD) is a major cause of late death and morbidity after allogeneic hematopoietic cell transplantation. Recently, in addition to Th2 cells, Th1 and Th17 cells have been shown to contribute to chronic GVHD progression. IL-12 induces Th1 cells and IL-23 plays a role in stabilizing and/or amplifying Th17 cells, as well as in inducing IFN-/IL-17 double-producing cells. Because mAb targeting the p40 subunit common to both IL-12 and IL-23 can inhibit both IL-12R and IL-23R-mediated signaling, we investigated the effects of anti-p40 mAb on a well-defined chronic GVHD mice model. Treatment of anti-p40 mAb in allogeneic recipients significantly reduced the severity of clinical and pathological chronic GVHD. Intracellular staining revealed that IFN- single-positive (IL-17 – ) and IFN-/IL-17 double-positive cells were suppressed in anti-p40 mAb–treated allogeneic recipients compared with control recipients. The cytokine levels of IFN- and IL-17 were also decreased in serum from anti-p40 mAb–treated allogeneic recipients. T-bet expression of donor IL-17 + CD4 + T cells was reduced significantly in anti-p40 mAb–treated recipients, and this reduction in T-bet expression was associated with IL-22 production by donor T cells. These results suggested that anti-p40 mAb attenuated chronic GVHD via suppression of IFN-/IL-17–producing cells, and that targeting the IL-12/IL-23 pathway may represent a promising therapeutic strategy for preventing and treating chronic GVHD.

Description: NFIL3 is a transcription factor that regulates multiple immunologic functions. In myeloid cells, NFIL3 is IL-10 inducible and has a key role as a repressor of IL-12p40 transcription. NFIL3 is a susceptibility gene for the human inflammatory bowel diseases. In this article, we describe spontaneous colitis in Nfil3 –/– mice. Mice lacking both Nfil3 and Il10 had severe early-onset colitis, suggesting that NFIL3 and IL-10 independently regulate mucosal homeostasis. Lymphocytes were necessary for colitis, because Nfil3/Rag1 double-knockout mice were protected from disease. However, Nfil3/Rag1 double-knockout mice adoptively transferred with wild-type CD4 + T cells developed severe colitis compared with Rag1 –/– recipients, suggesting that colitis was linked to defects in innate immune cells. Colitis was abrogated in Nfil3/Il12b double-deficient mice, identifying Il12b dysregulation as a central pathogenic event. Finally, germ-free Nfil3 –/– mice do not develop colonic inflammation. Thus, NFIL3 is a microbiota-dependent, IL-10–independent regulator of mucosal homeostasis via IL-12p40.

Description: To prevent excessive inflammatory responses to commensal microbes, intestinal macrophages, unlike their systemic counterparts, do not produce inflammatory cytokines in response to enteric bacteria. Consequently, loss of macrophage tolerance to the enteric microbiota plays a central role in the pathogenesis of inflammatory bowel diseases. Therefore, we examined whether the hyporesponsive phenotype of intestinal macrophages is programmed by prior exposure to the microbiota. IL-10, but not in vivo exposure to the microbiota, programs intestinal macrophage tolerance, because wild-type (WT) colonic macrophages from germ-free and specific pathogen-free (SPF)-derived mice produce IL-10, but not IL-12 p40, when activated with enteric bacteria. Basal and activated IL-10 expression is mediated through a MyD88-dependent pathway. Conversely, colonic macrophages from germ-free and SPF-derived colitis-prone Il10 –/– mice demonstrated robust production of IL-12 p40. Next, mechanisms through which IL-10 inhibits Il12b expression were investigated. Although Il12b mRNA was transiently induced in LPS-activated WT bone marrow-derived macrophages (BMDMs), expression persisted in Il10 –/– BMDMs. There were no differences in nucleosome remodeling, mRNA stability, NF-B activation, or MAPK signaling to explain prolonged transcription of Il12b in Il10 –/– BMDMs. However, acetylated histone H4 transiently associated with the Il12b promoter in WT BMDMs, whereas association of these factors was prolonged in Il10 –/– BMDMs. Experiments using histone deacetylase (HDAC) inhibitors and HDAC3 short hairpin RNA indicate that HDAC3 is involved in histone deacetylation of the Il12b promoter by IL-10. These results suggest that histone deacetylation on the Il12b promoter by HDAC3 mediates homeostatic effects of IL-10 in macrophages.