Antigen Complexed with a TLR9 Agonist Bolsters c-Myc and mTORC1 Activity in Germinal Center B Lymphocytes.

The germinal center (GC) is the anatomical site where humoral immunity evolves. B cells undergo cycles of proliferation and selection to produce high-affinity Abs against Ag. Direct linkage of a TLR9 agonist (CpG) to a T-dependent Ag increases the number of GC B cells. We used a T-dependent Ag complexed with CpG and a genetic model for ablating the TLR9 signaling adaptor molecule MyD88 specifically in B cells (B-MyD88- mice) together with transcriptomics to determine how this innate pathway positively regulates the GC. GC B cells from complex Ag-immunized B-MyD88- mice were defective in inducing gene expression signatures downstream of c-Myc and mTORC1. In agreement with the latter gene signature, ribosomal protein S6 phosphorylation was increased in GC B cells from wild-type mice compared with B-MyD88- mice. However, GC B cell expression of a c-Myc protein reporter was enhanced by CpG attached to Ag in both wild-type and B-MyD88- mice, indicating a B cell-extrinsic effect on c-Myc protein expression combined with a B cell-intrinsic enhancement of gene expression downstream of c-Myc. Both mTORC1 activity and c-Myc are directly induced by T cell help, indicating that TLR9 signaling in GC B cells either enhances their access to T cell help or directly influences these pathways to further enhance the effect of T cell help. Taken together, these findings indicate that TLR9 signaling in the GC could provide a surrogate prosurvival stimulus, "TLR help," thus lowering the threshold for selection and increasing the magnitude of the GC response

Stimulation of κ Light-Chain Gene Rearrangement by the Immunoglobulin, µ Heavy Chain in a Pre-B-Cell Line

B-lymphocyte development exhibits a characteristic order of immunoglobulin gene rearrangements. Previous work has led to the hypothesis that expression of the immunoglobulin µ heavy chain induces rearrangement activity at the K light-chain locus. To examine this issue in more detail, we isolated five matched pairs of µ^- and endogenously rearranged µ^+ cell lines from the Abelson murine leukemia virus-transformed pro-B-cell line K.40. In four of the five µ^+ cell lines, substantial expression of µ protein on the cell surface was observed, and this correlated with an enhanced frequency of K immunoglobulin gene rearrangement compared with that in the matched µ^- cell lines. This increased K gene rearrangement frequency was not due to a general increase in the amount of V(D)J recombinase activity in the µ^+ cells. Consistently, introduction of a functionally rearranged µ gene into one of the µ^- pre-B-cell lines resulted in a fivefold increase in K gene rearrangements. In three of the four clonally matched pairs with increased K gene rearrangements, the increase in rearrangement frequency was not accompanied by a significant increase in germ line transcripts from the C_K locus. However, in the fourth pair, K.40D, we observed an increase in germ line transcription of the kappa locus after expression of µ protein encoded by either an endogenously rearranged or a transfected functional heavy-chain allele. In these cells, the amount of the germ line C_K transcript correlated with the measured frequency of rearranged K genes. These results support a regulated model of B-cell development in which µ protein expression in some way targets the V(D)J recombinase to the K gene locus

Myeloid cells, BAFF, and IFN-γ establish an inflammatory loop that exacerbates autoimmunity in Lyn-deficient mice

Autoimmunity is traditionally attributed to altered lymphoid cell selection and/or tolerance, whereas the contribution of innate immune cells is less well understood. Autoimmunity is also associated with increased levels of B cell–activating factor of the TNF family (BAFF; also known as B lymphocyte stimulator), a cytokine that promotes survival of self-reactive B cell clones. We describe an important role for myeloid cells in autoimmune disease progression. Using Lyn-deficient mice, we show that overproduction of BAFF by hyperactive myeloid cells contributes to inflammation and autoimmunity in part by acting directly on T cells to induce the release of IFN-γ. Genetic deletion of IFN-γ or reduction of BAFF activity, achieved by either reducing myeloid cell hyperproduction or by treating with an anti-BAFF monoclonal antibody, reduced disease development in lyn−/− mice. The increased production of IFN-γ in lyn−/− mice feeds back on the myeloid cells to further stimulate BAFF release. Expression of BAFF receptor on T cells was required for their full activation and IFN-γ release. Overall, our data suggest that the reciprocal production of BAFF and IFN-γ establishes an inflammatory loop between myeloid cells and T cells that exacerbates autoimmunity in this model. Our findings uncover an important pathological role of BAFF in autoimmune disorders

A Critical Role for Syk in Signal Transduction and Phagocytosis Mediated by Fcγ Receptors on Macrophages

Receptors on macrophages for the Fc region of IgG (FcγR) mediate a number of responses important for host immunity. Signaling events necessary for these responses are likely initiated by the activation of Src-family and Syk-family tyrosine kinases after FcγR cross-linking. Macrophages derived from Syk-deficient (Syk−) mice were defective in phagocytosis of particles bound by FcγRs, as well as in many FcγR-induced signaling events, including tyrosine phosphorylation of a number of cellular substrates and activation of MAP kinases. In contrast, Syk− macrophages exhibited normal responses to another potent macrophage stimulus, lipopolysaccharide. Phagocytosis of latex beads and Escherichia coli bacteria was also not affected. Syk− macrophages exhibited formation of polymerized actin structures opposing particles bound to the cells by FcγRs (actin cups), but failed to proceed to internalization. Interestingly, inhibitors of phosphatidylinositol 3-kinase also blocked FcγR-mediated phagocytosis at this stage. Thus, PI 3-kinase may participate in a Syk-dependent signaling pathway critical for FcγR-mediated phagocytosis. Macrophages derived from mice deficient for the three members of the Src-family of kinases expressed in these cells, Hck, Fgr, and Lyn, exhibited poor Syk activation upon FcγR engagement, accompanied by a delay in FcγR-mediated phagocytosis. These observations demonstrate that Syk is critical for FcγR-mediated phagocytosis, as well as for signal transduction in macrophages. Additionally, our findings provide evidence to support a model of sequential tyrosine kinase activation by FcγR's analogous to models of signaling by the B and T cell antigen receptors

MyD88-dependent interplay between myeloid and endothelial cells in the initiation and progression of obesity-associated inflammatory diseases.

Low-grade systemic inflammation is often associated with metabolic syndrome, which plays a critical role in the development of the obesity-associated inflammatory diseases, including insulin resistance and atherosclerosis. Here, we investigate how Toll-like receptor-MyD88 signaling in myeloid and endothelial cells coordinately participates in the initiation and progression of high fat diet-induced systemic inflammation and metabolic inflammatory diseases. MyD88 deficiency in myeloid cells inhibits macrophage recruitment to adipose tissue and their switch to an M1-like phenotype. This is accompanied by substantially reduced diet-induced systemic inflammation, insulin resistance, and atherosclerosis. MyD88 deficiency in endothelial cells results in a moderate reduction in diet-induced adipose macrophage infiltration and M1 polarization, selective insulin sensitivity in adipose tissue, and amelioration of spontaneous atherosclerosis. Both in vivo and ex vivo studies suggest that MyD88-dependent GM-CSF production from the endothelial cells might play a critical role in the initiation of obesity-associated inflammation and development of atherosclerosis by priming the monocytes in the adipose and arterial tissues to differentiate into M1-like inflammatory macrophages. Collectively, these results implicate a critical MyD88-dependent interplay between myeloid and endothelial cells in the initiation and progression of obesity-associated inflammatory diseases

The Blue Cross Blue Shield of Michigan Cardiovascular Consortium (BMC2) Collaborative Quality Improvement Initiative in Percutaneous Coronary Interventions

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72388/1/j.1540-8183.2002.tb01071.x.pd

Use of prasugrel vs clopidogrel and outcomes in patients with acute coronary syndrome undergoing percutaneous coronary intervention in contemporary clinical practice: Results from the PROMETHEUS study.

BACKGROUND AND OBJECTIVES: We sought to determine the frequency of use and association between prasugrel and outcomes in acute coronary syndrome patients undergoing percutaneous coronary intervention (PCI) in clinical practice. METHODS: PROMETHEUS was a multicenter observational registry of acute coronary syndrome patients undergoing PCI from 8 centers in the United States that maintained a prospective PCI registry for patient outcomes. The primary end points were major adverse cardiovascular events at 90days, a composite of all-cause death, nonfatal myocardial infarction, stroke, or unplanned revascularization. Major bleeding was defined as any bleeding requiring hospitalization or blood transfusion. Hazard ratios (HRs) were generated using multivariable Cox regression and stratified by the propensity to treat with prasugrel. RESULTS: Of 19,914 patients (mean age 64.4years, 32% female), 4,058 received prasugrel (20%) and 15,856 received clopidogrel (80%). Prasugrel-treated patients were younger with fewer comorbid risk factors compared with their counterparts receiving clopidogrel. At 90days, there was a significant association between prasugrel use and lower major adverse cardiovascular event (5.7% vs 9.6%, HR 0.58, 95% CI 0.50-0.67, P<.0001) and bleeding (1.9% vs 2.9%, HR 0.65, 95% CI 0.51-0.83, P<.001). After propensity stratification, associations were attenuated and no longer significant for either outcome. Results remained consistent using different approaches to adjusting for potential confounders. CONCLUSIONS: In contemporary clinical practice, patients receiving prasugrel tend to have a lower-risk profile compared with those receiving clopidogrel. The lower ischemic and bleeding events associated with prasugrel use were no longer evident after accounting for these baseline differences