Epigenetically Mediated Pathogenic Effects of Phenanthrene on Regulatory T Cells

Phenanthrene (Phe), a polycyclic aromatic hydrocarbon (PAH), is a major constituent of urban air pollution. There have been conflicting results regarding the role of other AhR ligands 2,3,7,8- tetrachlorodibenzo-p-dioxin (TCDD) and 6-formylindolo [3,2-b]carbazole (FICZ) in modifying regulatory T cell populations (Treg) or T helper (Th)17 differentiation, and the effects of Phe have been understudied. We hypothesized that different chemical entities of PAH induce Treg to become either Th2 or Th17 effector T cells through epigenetic modification of FOXP3. To determine specific effects on T cell populations by phenanthrene, primary human Treg were treated with Phe, TCDD, or FICZ and assessed for function, gene expression, and phenotype. Methylation of CpG sites within the FOXP3 locus reduced FOXP3 expression, leading to impaired Treg function and conversion of Treg into a CD4+CD25lo Th2 phenotype in Phe-treated cells. Conversely, TCDD treatment led to epigenetic modification of IL-17A and conversion of Treg to Th17 T cells. These findings present a mechanism by which exposure to AhR-ligands mediates human T cell responses and begins to elucidate the relationship between environmental exposures, immune modulation, and initiation of human disease

The surface-anchored NanA protein promotes pneumococcal brain endothelial cell invasion

In humans, Streptococcus pneumoniae (SPN) is the leading cause of bacterial meningitis, a disease with high attributable mortality and frequent permanent neurological sequelae. The molecular mechanisms underlying the central nervous system tropism of SPN are incompletely understood, but include a primary interaction of the pathogen with the blood–brain barrier (BBB) endothelium. All SPN strains possess a gene encoding the surface-anchored sialidase (neuraminidase) NanA, which cleaves sialic acid on host cells and proteins. Here, we use an isogenic SPN NanA-deficient mutant and heterologous expression of the protein to show that NanA is both necessary and sufficient to promote SPN adherence to and invasion of human brain microvascular endothelial cells (hBMECs). NanA-mediated hBMEC invasion depends only partially on sialidase activity, whereas the N-terminal lectinlike domain of the protein plays a critical role. NanA promotes SPN–BBB interaction in a murine infection model, identifying the protein as proximal mediator of CNS entry by the pathogen

Sialic acid O-acetylation in group B Streptococcus : impact on pathogen-host interactions

Group B Streptococcus (GBS) asymptomatically colonizes the lower gastrointestinal and urogenital tracts in 25-35% of the human population. However, in immune compromised individuals and infants, GBS is able to cause severe invasive disease and death. In newborns, GBS is the leading cause of sepsis and meningitis. GBS is surrounded by a thick capsular polysaccharide (CPS) layer. Nine antigenically distinct serotypes have been documented, all of which display a terminal [alpha]2-3 linked sialic acid (Sia) residue. This residue is key to GBS evasion of host immune response, and as such, is a key virulence factor for the bacterium. Terminal Sias are commonly expressed on the surface of mammalian cells and in this context serve to dampen immune response against self. This is accomplished by binding to factor H, which regulates the alternative complement pathway, as well as through interactions with Siglecs, Sia binding receptors with immunomodulatory capabilities, on the surface of immune cells. Sialic acid on the surface of GBS similarly engages these immune-suppressive mechanisms in a highly effective form of molecularly mimicry. It has only recently been discovered that GBS biochemically modifies terminal Sia residues by adding an O-acetylationetyl group to the C-7 position of the Sia moiety. Acetylation is incomplete, ranging from 5 to 40% of total surface Sia residues, and is characteristic of different serotype strains. This level is controlled by the balance in activities of the NeuD acetyltransferase and NeuA acetylesterase. Both enzymes are dual functional, being required for surface sialylation as well as acetylation. In this work we develop methodology using genetic techniques to manipulate O-acetylationetylation (O-acetylation) without impacting overall surface sialylation. Using isogenic strains with artificially high and low O-acetylation we proceed to analyze the impact of O-acetylation on various biological interactions and ultimate consequence for GBS virulence. We find that O-acetylation protects GBS surface Sias from removal by various microbial sialidases, presenting a possible benefit to in the context of colonization. Looking at Sia-dependent immune interactions, we discover that GBS O-acetylation does not impact alternative complement pathway activation, with both OAchigh and OAclow strains showing identical Sia-dependent deposition of the active opsonin C3b. O-acetylation does impair interactions with Siglec-9, thereby impairing the ability of GBS to downregulate neutrophil responses. In this regard,we document increased elastase secretion, oxidative burst and bacterial killing by neutrophils in response to the OAchigh strain. In the more complex context of ex-vivo human whole blood, these differences are enhanced, with the OAchigh strain being killed more rapidly. The OAchigh strain also shows greatly attenuated virulence in a mouse IP model of infection. Thus, in the context of invasion O- acetylation appears to be a cost to bacterial survival. Finally we document O-acetylation levels in 100 clinical and colonizing type Ia and type III GBS isolates. We find that type Ia strains consistently show very low levels of O-acetylation (5%) while type III strains display much higher O-acetylation (30%). This is correlated with the NeuD allele, possessing high or low enzymatic activity. We hypothesize that the distinct O-acetylation levels in type Ia and type III strains represent a balance between opposing forcing of selection, which differ in these different genetic backgrounds. Further studies will be necessary to elucidate these unique constraints, and their implications in disease manifestatio

Epigenetically Mediated Pathogenic Effects of Phenanthrene on Regulatory T Cells

Phenanthrene (Phe), a polycyclic aromatic hydrocarbon (PAH), is a major constituent of urban air pollution. There have been conflicting results regarding the role of other AhR ligands 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 6-formylindolo [3,2-b]carbazole (FICZ) in modifying regulatory T cell populations (Treg) or T helper (Th)17 differentiation, and the effects of Phe have been understudied. We hypothesized that different chemical entities of PAH induce Treg to become either Th2 or Th17 effector T cells through epigenetic modification of FOXP3. To determine specific effects on T cell populations by phenanthrene, primary human Treg were treated with Phe, TCDD, or FICZ and assessed for function, gene expression, and phenotype. Methylation of CpG sites within the FOXP3 locus reduced FOXP3 expression, leading to impaired Treg function and conversion of Treg into a CD4 + CD25 lo Th2 phenotype in Phe-treated cells. Conversely, TCDD treatment led to epigenetic modification of IL-17A and conversion of Treg to Th17 T cells. These findings present a mechanism by which exposure to AhR-ligands mediates human T cell responses and begins to elucidate the relationship between environmental exposures, immune modulation, and initiation of human disease

Outcomes in CCG-2961, a Children's Oncology Group Phase 3 Trial for untreated pediatric acute myeloid leukemia: a report from the Children's Oncology Group

CCG-2961 incorporated 3 new agents, idarubicin, fludarabine and interleukin-2, into a phase 3 AML trial using intensive-timing remission induction/consolidation and related donor marrow transplantation or high-dose cytarabine intensifi-cation. Among 901 patients under age 21 years, 5-year survival was 52%, and event-free survival was 42%. Survival improved from 44% between 1996 and 1998 to 58% between 2000 and 2002 (P = .005), and treatment-related mortality declined from 19% to 12% (P = .025). Partial replacement of daunomycin with idarubicin in the 5-drug induction combination achieved a remission rate of 88%, similar to historical controls. Postremission survival was 56% in patients randomized to either 5-drug reinduction or fludarabine/cytarabine/idarubicin. For patients with or without a related donor, respective 5-year disease-free survival was 61% and 50% (P = .021); respective survival was 68% and 62% (P = .425). Donor availability conferred no benefit on those with inv(16) or t(8;21) cytogenetics. After cytarabine intensification, patients randomized to interleukin-2 or none experienced similar outcomes. Factors predictive of inferior survival were age more than 16 years, non-white ethnicity, absence of related donor, obesity, white blood cell count more than 100 000 × 109/L, −7/7q−, −5/5q−, and/or complex karyotype. No new agent improved outcomes; experience may have contributed to better results time