The ubiquitin ligase XIAP recruits LUBAC for NOD2 signaling in inflammation and innate immunity

Nucleotide-binding and oligomerization domain (NOD)-like receptors constitute a first line of defense against invading bacteria. X-linked Inhibitor of Apoptosis (XIAP) is implicated in the control of bacterial infections, and mutations in XIAP are causally linked to immunodeficiency in X-linked lymphoproliferative syndrome type-2 (XLP-2). Here, we demonstrate that the RING domain of XIAP is essential for NOD2 signaling and that XIAP contributes to exacerbation of inflammation-induced hepatitis in experimental mice. We find that XIAP ubiquitylates RIPK2 and recruits the linear ubiquitin chain assembly complex (LUBAC) to NOD2. We further show that LUBAC activity is required for efficient NF-κB activation and secretion of proinflammatory cytokines after NOD2 stimulation. Remarkably, XLP-2-derived XIAP variants have impaired ubiquitin ligase activity, fail to ubiquitylate RIPK2, and cannot facilitate NOD2 signaling. We conclude that XIAP and LUBAC constitute essential ubiquitin ligases in NOD2-mediated inflammatory signaling and propose that deregulation of NOD2 signaling contributes to XLP-2 pathogenesis.

The Emerging Role of TLR and Innate Immunity in Cardiovascular Disease

Cardiovascular disease is a complex disorder involving multiple pathophysiological processes, several of which involve activation of toll-like receptors (TLRs) of the innate immune system. As sentinels of innate immunity TLRs are nonclonally germline-encoded molecular pattern recognition receptors that recognize exogenous as well as tissue-derived molecular dangers signals promoting inflammation. In addition to their expression in immune cells, TLRs are found in other tissues and cell types including cardiomyocytes, endothelial and vascular smooth muscle cells. TLRs are differentially regulated in various cell types by several cardiovascular risk factors such as hypercholesterolemia, hyperlipidemia, and hyperglycemia and may represent a key mechanism linking chronic inflammation, cardiovascular disease progression, and activation of the immune system. Modulation of TLR signaling by specific TLR agonists or antagonists, alone or in combination, may be a useful therapeutic approach to treat various cardiovascular inflammatory conditions such as atherosclerosis, peripheral arterial disease, secondary microvascular complications of diabetes, autoimmune disease, and ischemia reperfusion injury. In this paper we discuss recent developments and current evidence for the role of TLR in cardiovascular disease as well as the therapeutic potential of various compounds on inhibition of TLR-mediated inflammatory responses.

The habitat, double life, citizenship, and forgetfulness of IgA

Immunoglobulin A (IgA) is the main secretory immunoglobulin of mucous membranes and is powerfully induced by the presence of commensal microbes in the intestine. B cells undergo class switch recombination to IgA in the mucosa-associated lymphoid tissues, particularly mesenteric lymph nodes (MLNs) and Peyer's patches, through both T-dependent and T-independent pathways. IgA B cells primed in the mucosa traffic from the intestinal lymphoid structures, initially through the lymphatics and then join the bloodstream, to home back to the intestinal mucosa as IgA-secreting plasma cells. Once induced, anti-bacterial IgA can be extremely long-lived but is replaced if there is induction of additional IgA specificities by other microbes. The mucosal immune system is anatomically separated from the systemic immune system by the MLNs, which act as a firewall to prevent penetration of live intestinal bacteria to systemic sites. Dendritic cells sample intestinal bacteria and induce B cells to switch to IgA. In contrast, intestinal macrophages are adept at killing extracellular bacteria and are able to clear bacteria that have crossed the mucus and epithelial barriers. There is both a continuum between innate and adaptive immune mechanisms and compartmentalization of the mucosal immune system from systemic immunity that function to preserve host microbial mutualism.

Determinants of hepatitis A vaccine immunity in a cohort of human immunodeficiency virus-infected children living in Switzerland

Vaccination in HIV-infected children is often less effective than in healthy children. The goal of this study was to assess vaccine responses to hepatitis A virus (HAV) in HIV-infected children. Children of the Swiss Mother and Child HIV Cohort Study (MoCHiV) were enrolled prospectively. Recommendations for initial, catch-up, and additional HAV immunizations were based upon baseline antibody concentrations and vaccine history. HAV IgG was assessed by enzyme-linked immunosorbent assay (ELISA) with a protective cutoff value defined as ≥10 mIU/ml. Eighty-seven patients were included (median age, 11 years; range, 3.4 to 21.2 years). Forty-two patients were seropositive (48.3%) for HAV. Among 45 (51.7%) seronegative patients, 36 had not received any HAV vaccine dose and were considered naïve. Vaccine responses were assessed after the first dose in 29/35 naïve patients and after the second dose in 33/39 children (25 initially naïve patients, 4 seronegative patients, and 4 seropositive patients that had already received 1 dose of vaccine). Seroconversion was 86% after 1 dose and 97% after 2 doses, with a geometric mean concentration of 962 mIU/ml after the second dose. A baseline CD4(+) T cell count below 750 cells/μl significantly reduced the post-2nd-dose response (P = 0.005). Despite a high rate of seroconversion, patients with CD4(+) T cell counts of <750/μl had lower anti-HAV antibody concentrations. This may translate into a shorter protection time. Hence, monitoring humoral immunity may be necessary to provide supplementary doses as needed.

Homeland security: IgA immunity at the frontiers of the body

IgA is the most abundant immunoglobulin produced in mammals, and is mostly secreted across mucous membranes. At these frontiers, which are constantly assaulted by pathogenic and commensal microbes, IgA provides part of a layered system of immune protection. In this review, we describe how IgA induction occurs through both T-dependent and T-independent mechanisms, and how IgA is generated against the prodigious load of commensal microbes after mucosal dendritic cells (DCs) have sampled a tiny fraction of the microbial consortia in the intestinal lumen. To function in this hostile environment, IgA must be induced behind the 'firewall' of the mesenteric lymph nodes to generate responses that integrate microbial stimuli, rather than the classical prime-boost effects characteristic of systemic immunity.

Innate and adaptive immunity in host-microbiota mutualism

Healthy individuals live in peaceful co-existence with an immense load of intestinal bacteria. This symbiosis is advantageous for both the host and the bacteria. For the host it provides access to otherwise undigestible nutrients and colonization resistance against pathogens. In return the bacteria receive an excellent nutrient habitat. The mucosal immune adaptations to the presence of this commensal intestinal microflora are manifold. Although bacterial colonization has clear systemic consequences, such as maturation of the immune system, it is striking that the mutualistic adaptive (T and B cells) and innate immune responses are precisely compartmentalized to the mucosal immune system. Here we summarize the mechanisms of mucosal immune compartmentalization and its importance for a healthy host-microbiota mutualism.

From endoplasmic reticulum to secretory granules: role of zinc in the secretory pathway of growth hormone

Endocrine and neuroendocrine cells differ from cells which rapidly release all their secreted proteins in that they store some secretory proteins in concentrated forms in secretory granules to be rapidly released when cells are stimulated. Protein aggregation is considered as the first step in the secretory granule biosynthesis and, at least in the case of prolactin and growth hormone, greatly depends on zinc ions that facilitate this process. Hence, regulation of cellular zinc transport especially that within the regulated secretory pathway is of importance to understand. Various zinc transporters of Slc30a/ZnT and Slc39a/Zip families have been reported to fulfil this role and to participate in fine tuning of zinc transport in and out of the endoplasmic reticulum, Golgi complex and secretory granules, the main cellular compartments of the regulated secretory pathway. In this review, we will focus on the role of zinc in the formation of hormone-containing secretory granules with special emphasis on conditions required for growth hormone dimerization/aggregation. In addition, we highlight the role of zinc transporters that govern the process of zinc homeostasis in the regulated hormone secretion.

Cellular immunity in healthy volunteers treated with an octavalent conjugate Pseudomonas aeruginosa vaccine

Humoral immunity in response to an octavalent O-polysaccharide-toxin A conjugate Pseudomonas aeruginosa vaccine is well studied, and a phase III clinical study in cystic fibrosis (CF) patients is currently ongoing. In contrast, little is known about cellular immunity induced by this vaccine. Fifteen healthy volunteers were immunized on days 1 and 60. Parameters of cellular immunity were studied before vaccination on day 1, and on day 74. Analyses included flow cytometry of whole blood and antigen-induced proliferation of and cytokine production by lymphocyte cultures. The effects of immunization on the composition of peripheral blood lymphocytes as determined by flow cytometry were minor. In contrast, after immunization a highly significant increase of proliferation in response to stimulation with detoxified toxin A was noted: the stimulation index rose from 1.4 on day 1 to 42.2 on day 74 (restimulation with 0.4 microg/ml; P = 0.003). Immunization led to significant production of interferon (IFN)-gamma and tumour necrosis factor (TNF)-alpha by antigen-stimulated lymphocytes. In contrast, no significant induction of interleukin (IL)-4 or IL-10 was observed. In conclusion, immunization of healthy volunteers led to activation of cellular immunity including strong antigen-specific proliferation and cytokine production. In CF patients priming of the cellular immune system towards a Th1-like pattern would be of potential advantage. Therefore, confirmatory analyses in immunized CF patients with and without chronic infection with P. aeruginosa are foreseen.

Leiomyomatoid angiomatous neuroendocrine tumor (LANT) of the pituitary: a distinctive biphasic neoplasm with primitive secretory phenotype and smooth muscle-rich stroma

We describe a hitherto undocumented variant of dimorphic pituitary neoplasm composed of an admixture of neurosecretory cells and profuse leiomyomatous stroma around intratumoral vessels. Radiologically perceived as a macroadenoma of 3.8 cm in diameter, this pituitary mass developed in an otherwise healthy 43-year-old female. At the term of a yearlong history of amenorrhea and progressive bitemporal visual loss, subtotal resection was performed via transsphenoidal microsurgery. Discounting mild hyperprolactinemia, there was no evidence of excess hormone production. Histologically, solid sheets, nests and cords of epithelial-looking, yet cytokeratin-negative cells were seen growing in a richly vascularized stroma of spindle cells. While strong immunoreactivity for NCAM, Synaptophysin and Chromogranin-A was detected in the former, the latter showed both morphological and immunophenotypic hallmarks of smooth muscle, being positive for vimentin, muscle actin and smooth muscle actin. Architectural patterns varied from monomorphous stroma-dominant zones through biphasic neuroendocrine-leiomyomatous areas, to pseudopapillary fronds along vascular cores. Only endothelia were labeled with CD34. Staining for S100 protein and GFAP, characteristics of sustentacular cells, as well as bcl-2 and c-kit was absent. Except for alpha-subunit, anterior pituitary hormones tested negative in tumor cells, as did a panel of peripheral endocrine markers, including serotonin, somatostatin, calcitonin, parathormone and vasoactive intestinal polypeptide. Mitotic activity was absent and the MIB-1 labeling index low (1-2%). While assignment of this lesion to any established neoplastic entity is not forthcoming, we propose it is being considered as a low-grade neuroendocrine tumor possibly related to null cell adenoma.