Microglial regulation of immunological and neuroprotective functions of astroglia

Microglia and astroglia play critical roles in the development, function, and survival of neurons in the CNS. However, under inflammatory conditions the role of astrogliosis in the inflammatory process and its effects on neurons remains unclear. Here, we used several types of cell cultures treated with the bacterial inflammogen LPS to address these questions. We found that the presence of astroglia reduced inflammation‐driven neurotoxicity, suggesting that astrogliosis is principally neuroprotective. Neutralization of supernatant glial cell line‐derived neurotrophic factor (GDNF) released from astroglia significantly reduced this neuroprotective effect during inflammation. To determine the immunological role of astroglia, we optimized a highly‐enriched astroglial culture protocol and demonstrated that LPS failed to induce the synthesis and release of TNF‐α and iNOS/NO. Instead we found significant enhancement of TNF‐α and iNOS expression in highly‐enriched astroglial cultures required the presence of 0.5–1% microglia, respectively. Thus suggesting that microglial‐astroglial interactions are required for LPS to induce the expression of pro‐inflammatory factors and GDNF from astroglia. Specifically, we found that microglia‐derived TNF‐α plays a pivotal role as a paracrine signal to regulate the neuroprotective functions of astrogliosis. Taken together, these findings suggest that astroglia may not possess the ability to directly recognize the innate immune stimuli LPS, but rather depend on crosstalk with microglia to elicit release of neurotrophic factors as a counterbalance to support neuronal survival from the collateral damage generated by activated microglia during neuroinflammation. GLIA 2015;63:118–131     

Increased frequency of T cell receptor V alpha 12.1 expression on CD8+ T cells: evidence that V alpha participates in shaping the peripheral T cell repertoire.

The T cell receptor repertoire has a potential for vast diversity. However, this diversity is limited by the fact that the majority of thymocytes die as the repertoire is shaped by positive and negative selection events during development. Such thymic selection affecting TCR V beta gene segment usage has been demonstrated in the mouse. However, similar data has not been forthcoming in man, and little is known about the role of the TCR alpha chain in antigen/major histocompatibility complex (MHC) recognition in any species. Here, we used a monoclonal antibody recognizing the TCR V alpha 12.1 gene product to assess the expression of this gene in the peripheral blood of man. In most individuals tested, the percentage of cells expressing V alpha 12.1 was significantly higher in CD8+ T cells than in CD4+ T cells. That the V alpha gene product itself was responsible for this increased expression in CD8+ T cells was underscored by the lack of substantial skewing of V beta usage in the V alpha 12.1-bearing T cells. Moreover, the skewed expression of V alpha 12.1 was already present at birth, indicating that it was likely to be due to a developmental process rather than the result of exposure to environmental antigens. Based on the established role for CD8 in binding to class I MHC molecules, we suggest that increased expression of V alpha 12.1 on CD8+ T cells points to a role for TCR's using V alpha 12.1 in class I MHC/Ag recognition. These results indicate that V alpha gene usage in the peripheral blood of man is not random, and they support a role for V alpha as a participant in the self-MHC recognition process that shapes the TCR repertoire.     

Bayesian meta-analysis across genome-wide association studies of diverse phenotypes

Genome-wide association studies (GWAS) are a powerful tool for understanding the genetic basis of diseases and traits, but most studies have been conducted in isolation, with a focus on either a single or a set of closely related phenotypes. We describe MetABF, a simple Bayesian framework for performing integrative meta-analysis across multiple GWAS using summary statistics. The approach is applicable across a wide range of study designs and can increase the power by 50% compared with standard frequentist tests when only a subset of studies have a true effect. We demonstrate its utility in a meta-analysis of 20 diverse GWAS which were part of the Wellcome Trust Case Control Consortium 2. The novelty of the approach is its ability to explore, and assess the evidence for a range of possible true patterns of association across studies in a computationally efficient framework.     

Infections caused by aterial catheters used for hemodynamic monitoring

Utilizing a semiquantitative technique for culturing vascular catheters, we prospectively studied the risk and profile of infection caused by arterial catheters used for hemodynamic monitoring in 95 patients with a high risk of nosocomial infection. Of 130 catheters, 23 (18 per cent) produced local infection (larger than or equal to 15 colonies on semi-quantitative culture) and five septicemia (4 per cent). Sixteen of the 23 local infections and all septicemias occurred with catheter placements exceeding four days (p less than 0.001). Other factors associated with an increased risk of infection included insertion by surgical cut-down rather than percutaneously (ninefold increased rate of bacteremia, p = 0.008) and the presence of local inflammation (12-fold increase, p = 0.009). Systemic antimicrobial therapy (given to 80 per cent of the entire group and to four of the five with septicemia) did not protect against catheter-related infection but may account for the predominance of enterococci, Candida and gram-negative bacilli in these infections. Twelve per cent of all nosocomial bacteremias occurring in this critical care unit population originated from an arterial catheter. Indwelling arterial catheters pose a significant risk of bacteremic infection to ctirically ill patients. The percutaneous mode of placement is preferred; when prolonged arterial cannulation is required, the site should be rotated every four days. Local pain or inflammation, or clinical signs of sepsis without an obvious source should prompt removal and culture of the catheter.     

Microangiopathic hemolytic anemia, renal failure, and noncardiogenic pulmonary edema: a chemotherapy-induced syndrome

Following gastrectomy for locally advanced adenocarcinomas, three patients developed microangiopathic hemolytic anemia and renal failure shortly after completing courses of adjuvant chemotherapy with mitomycin and 5-FU. These complications progressed despite cessation of chemotherapy, and all three patients died of noncardiogenic pulmonary edema precipitated in two cases by blood transfusions. At autopsy, two patients had no residual carcinoma and all had a diffuse microangiopathy involving mainly the kidneys and lungs. There was intimal hyperplasia of many arterioles sometimes associated with complete occlusion of the lumen, prominent nuclear atypia in many capillary cells, and numerous capillary fibrin thrombi. Direct immunofluorescence studies revealed extensive fibrinogen-fibrin deposits in the vascular lesions. Chemotherapy-induced microangiopathic hemolytic anemia and renal failure may predispose patients to fatal episodes of noncardiogenic pulmonary edema that can be triggered by blood transfusions.     

Gamma delta T lymphocytes in human tuberculosis.

The manifestations of tuberculous infection reflect the immune response to infection. Most healthy tuberculin reactors develop protective immunity; tuberculous pleuritis reflects a resistant response manifest by mild disease, whereas advanced pulmonary and miliary tuberculosis reflect ineffective immunity. The role of gamma delta T cells was assessed in tuberculous infection by evaluating expansion of these cells from blood mononuclear cells after stimulation with Mycobacterium tuberculosis. After culture in vitro, the percentages of gamma delta+ cells were significantly greater in patients with protective and resistant immunity (tuberculin reactors, 25% +/- 4%; tuberculous pleuritis, 30% +/- 7%) than in those with ineffective immunity (advanced pulmonary tuberculosis, 9% +/- 3%; miliary tuberculosis, 2% +/- 1%). In leprosy, expansion of gamma delta+ cells was greater in immunologically resistant tuberculoid patients (32% +/- 4%) than in Mycobacterium leprae-unresponsive lepromatous patients (9% +/- 2%). M. tuberculosis-reactive gamma delta T cell lines produced interferon-gamma, granulocyte-macrophage colony-stimulating factor, interleukin-3, and tumor necrosis factor-alpha, cytokines that activate macrophages and may contribute to mycobacterial elimination. These findings suggest that gamma delta T cells contribute to immune resistance against M. tuberculosis.     

Comparative organization of cattle chromosome 5 revealed by comparative mapping by annotation and sequence similarity and radiation hybrid mapping

A whole genome cattle-hamster radiation hybrid cell panel was used to construct a map of 54 markers located on bovine chromosome 5 (BTA5). Of the 54 markers, 34 are microsatellites selected from the cattle linkage map and 20 are genes. Among the 20 mapped genes, 10 are new assignments that were made by using the comparative mapping by annotation and sequence similarity strategy. A LOD-3 radiation hybrid framework map consisting of 21 markers was constructed. The relatively low retention frequency of markers on this chromosome (19%) prevented unambiguous ordering of the other 33 markers. The length of the map is 398.7 cR, corresponding to a ratio of approximately 2.8 cR(5,000)/cM. Type I genes were binned for comparison of gene order among cattle, humans, and mice. Multiple internal rearrangements within conserved syntenic groups were apparent upon comparison of gene order on BTA5 and HSA12 and HSA22. A similarly high number of rearrangements were observed between BTA5 and MMU6, MMU10, and MMU15. The detailed comparative map of BTA5 should facilitate identification of genes affecting economically important traits that have been mapped to this chromosome and should contribute to our understanding of mammalian chromosome evolution.