IgG carrying terminal α2,6-linked sialic acids added to conserved N-glycans within the Fc domain by the sialyltransferase ST6Gal1 accounts for the anti-inflammatory effects of large-dose i.v. Ig (IVIg) in autoimmunity. Here, B-cell-specific ablation of ST6Gal1 in mice revealed that IgG sialylation can occur in the extracellular environment of the bloodstream independently of the B-cell secretory pathway. We also discovered that secreted ST6Gal1 is produced by cells lining central veins in the liver and that IgG sialylation is powered by serum-localized nucleotide sugar donor CMP-sialic acid that is at least partially derived from degranulating platelets. Thus, antibody-secreting cells do not exclusively control the sialylationdependent anti-inflammatory function of IgG. Rather, IgG sialylation can be regulated by the liver and platelets through the corresponding release of enzyme and sugar donor into the cardiovascular circulation.W hile en route to the plasma membrane as integral membrane proteins or for secretion, glycoproteins exiting the endoplasmic reticulum traverse the cis-, medial-, and trans-Golgi apparatus where the associated N-linked glycans are remodeled into their final form. This classically defined secretory pathway dictates that the glycoform of all glycoproteins produced by a cell is largely determined by the cohort of enzymes within the Golgi and the metabolic circumstances of that specific cell.Protein glycosylation is known to play fundamental roles in all aspects of biology, but has recently gained significant attention in immunology. When administered at high doses, i.v. Ig (IVIg) is an effective anti-inflammatory treatment for autoimmune patients (1). In 2006, it was discovered that the ∼10% of IgG molecules that carry α2,6-linked sialic acids upon the conserved biantennary N-glycans within the Fc domain provided the potent IVIg anti-inflammatory activity in autoimmune disease (2). Indeed, enrichment for the sialylated IgG (sIgG) fraction from IVIg pools increased the efficacy of treatment in mouse models of arthritis 100-fold in an IL-4-dependent fashion through receptors such as CD209 (DC-SIGN) (3, 4). Moreover, it was reported that sialylation of IgG also impacts antibody affinity maturation, although the mechanism underlying this phenomenon remains to be fully elucidated (5). These data indicate that sialylation serves as the mechanism underlying pleotropic IgG function (3,4,6).Epidemiologic analyses published since the reports cited above are consistent with this model. For example, female rheumatoid arthritis patients often go into remission during pregnancy and then relapse following childbirth. Analysis of sIgG levels before, during, and after pregnancy showed that the level of sIgG increases rapidly during pregnancy-induced remission, whereas during periods of exacerbated disease, sIgG is essentially undetectable (7,8). To date, it is unclear whether IgG sialylation patterns precede or result from the inflammatory state, and essentially nothing is known about the regulatory mecha...

BackgroundUpregulation of pro-inflammatory cytokines has not only been associated with increased morbidity and mortality in older adults but also has been linked to frailty. In the current study we aimed to compare the relative relationship of age and frailty on inflammation and thrombosis in older veterans.ResultsWe analyzed 117 subjects (age range 62–95 years; median 81) divided into 3 cohorts: non-frail, pre-frail and frail based on the Fried phenotype of frailty. Serum inflammatory markers were determined using commercially available ELISA kits. Frail and pre-frail (PF) subjects had higher levels than non-frail (NF) subjects of IL-6 (NF vs. PF: p = 0.002; NF vs. F: p < 0.001), TNFR1 (NF vs. F: p = 0.012), TNFRII (NF vs. F: 0.002; NF vs. PF: p = 0.005) and inflammatory index: = 0.333*log(IL-6) + 0.666*log(sTNFR1) (NF vs. F: p = 0.009; NF vs. PF: p < 0.001). Frailty status explained a greater percent of variability in markers of inflammation than age: IL-6 (12 % vs. 0.3 %), TNFR1 (5 % vs. 4 %), TNFR2 (11 % vs. 6 %), inflammatory index (16 % vs. 8 %). Aging was significantly associated with higher fibrinogen (p = 0.04) and D-dimer levels (p = 0.01) but only among NF subjects.ConclusionIn conclusion, these data suggest that among older veterans, frailty status has a stronger association with inflammation and the inflammatory index than age does. Larger studies, in more diverse populations are needed to confirm these findings.

Carbohydrates, or glycans, are as integral to biology as nucleic acids and proteins. In immunology, glycans are well known to drive diverse functions ranging from glycosaminoglycan-mediated chemokine presentation and selectin-dependent leukocyte trafficking to the discrimination of self and non-self through the recognition of sialic acids by Siglec (sialic acid-binding Ig-like lectin) receptors. In recent years, a number of key immunological discoveries are driving a renewed and burgeoning appreciation for the importance of glycans. In this review, we highlight these findings which collectively help to define and refine our knowledge of the function and impact of glycans within the immune response.

Circulatory protein glycosylation is a biomarker of multiple disease and inflammatory states and has been applied in the clinic for liver dysfunction, heart disease and diabetes. With the notable exception of antibodies, the liver produces most of the circulatory glycoproteins, including the acute phase proteins released as a function of the inflammatory response. Among these proteins is β-galactoside α2,6-sialyltransferase (ST6Gal1), an enzyme required for α2,6-linked sialylation of glycoproteins. Here, we describe a hepatocyte-specific conditional knockout of ST6Gal1 (H-cKO) using albumin promoter-driven Cre-lox recombination. We confirm the loss of circulatory glycoprotein α2,6 sialylation and note no obvious dysfunction or pathology in young H-cKO mice, yet these mice show robust changes in plasma glycoprotein fucosylation, branching and the abundance of bisecting GlcNAc and marked changes in a number of metabolic pathways. As H-cKO mice aged, they spontaneously developed fatty liver disease characterized by the buildup of fat droplets in the liver, inflammatory cytokine production and a shift in liver leukocyte phenotype away from anti-inflammatory Kupffer cells and towards proinflammatory M1 macrophages. These findings connect hepatocyte and circulatory glycoprotein sialylation to the regulation of metabolism and inflammation, potentially identifying the glycome as a new target for liver-driven disease.

Despite effective control of HIV infection with antiretroviral drugs, individuals with HIV have high incidences of secondary diseases. These sequelae, such as cardiovascular disease (CVD), are poorly understood and represent a major health burden. To date, predictive biomarkers of HIV-associated secondary disease have been elusive, making preventative clinical management essentially impossible. Here, we applied a newly developed and easy to deploy, multitarget, and high-throughput glycomic analysis to banked HIV human plasma samples to determine whether the glycome may include biomarkers that predict future HIV-associated cardiovascular events or CVD diagnoses. Using 324 patient samples, we identified a glycomic fingerprint that was predictive of future CVD events but independent of CD4 counts, diabetes, age, and birth sex, suggesting that the plasma glycome may serve as a biomarker for specific HIV-associated sequelae. Our findings constitute the discovery of novel glycan biomarkers that could classify patients with HIV with elevated risk for CVD and reveal the untapped prognostic potential of the plasma glycome in human disease.-Oswald, D. M., Sim, E. S., Baker, C., Farhan, O., Debanne, S. M., Morris, N. J., Rodriguez, B. G., Jones, M. B., Cobb, B. A. Plasma glycomics predict cardiovascular disease in patients with ART-controlled HIV infections.

While Toll-like receptors (TLRs) represent one of the best characterized innate immune pathways, evidence suggests that TLRs are not restricted to innate leukocytes and some epithelial cells, but are also expressed in T cells. Specifically, published evidence focusing on FoxP3+ regulatory T cells demonstrate that they express functional TLR2, which is already known among the TLR family for its association with immune suppression; however, little is known about the relationship between T cell-intrinsic TLR2 binding and cytokine production, T cell differentiation, or T cell receptor (TCR) stimulation. Here, we demonstrate that TCR and TLR2 co-stimulation provides a T cell-intrinsic signal which generates a dramatic, synergistic cytokine response dominated by IL-10. Importantly, the response was not seen in either CD4+CD25+ or CD4+FoxP3+ Tregs, yet resulted in the expansion of a suppressive CD4+CD25+CD62L-CD44+CD45Rbhi effector/memory T cell subset not typically associated with immune inhibition. This study reveals the striking ability of a prototypical innate immune receptor to trigger a potent and suppressive IL-10 response in effector/memory T cells, supporting the notion that TLR2 is a co-regulatory receptor on T cells.

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The glycosylation of IgG has attracted increased attention due to the impact of N-glycan modifications at N297 on IgG function, acting primarily through modulation of Fc domain conformation and Fcγ receptor binding affinities and signaling. However, the mechanisms regulating IgG glycosylation and especially α2,6-sialylation of its N-glycan remain poorly understood. We observed previously that IgG is normally sialylated in mice with B cells lacking the sialyltransferase ST6Gal1. This supported the hypothesis that IgG may be sialylated outside of B cells, perhaps through the action of hepatocyte-released plasma ST6Gal1. Here we demonstrate that this model is incorrect. Animals lacking hepatocyte expressed ST6Gal1 retain normal IgG α2,6-sialylation, despite the lack of detectable ST6Gal1 in plasma. Moreover, we confirmed that B cells were not a redundant source of IgG sialylation. Thus, while α2,6-sialylation is lacking in IgG from mice with germline ablation of ST6Gal1, IgG α2,6-sialylation is normal in mice lacking ST6Gal1 in either hepatocytes or B cells. These results indicate that IgG α2,6-sialylation arises after release from a B cell, but is not dependent on plasma-localized ST6Gal1 activity.