Michael Fischer

Disruption of the Cr2 Locus Results in a Reduction in B-1a Cells and in an Impaired B Cell Response to T-Dependent Antigen

Covalent attachment of activated products of the third component of complement to antigen enhances its immunogenicity, but the mechanism is not clear. This effect is mediated by specific receptors, mCR1 (CD35) and mCR2 (CD21), expressed primarily on B cells and follicular dendritic cells in mice. To dissect the role of mCR1 and mCR2 in the humoral response, we have disrupted the Cr2 locus to generate mice deficient in both receptors. The deficient mice (Cr2-/-) were found to have a reduction in the CD5+ population of peritoneal B-1 cells, although their serum IgM levels were within the range of normal mice. Moreover, Cr2-/- mice had a severe defect in their humoral response to T-dependent antigens that was characterized by a reduction in serum antibody titers and in the number and size of germinal centers within splenic follicles. Reconstitution of the deficient mice with bone marrow from MHC-matched Cr2+/+ donors corrected the defect, demonstrating that the defect was due to B cells themselves. These results indicate an obligatory role of B cell complement receptors in responses of the B cells to protein antigens.

Populating a Release History Database from version control and bug tracking systems

Version control and bug tracking systems contain large amounts of historical information that can give deep insight into the evolution of a software project. Unfortunately, these systems provide only insufficient support for a detailed analysis of software evolution aspects. We address this problem and introduce an approach for populating a release history database that combines version data with bug tracking data and adds missing data not covered by version control systems such as merge points. Then simple queries can be applied to the structured data to obtain meaningful views showing the evolution of a software project. Such views enable more accurate reasoning of evolutionary aspects and facilitate the anticipation of software evolution. We demonstrate our approach on the large open source project Mozilla that offers great opportunities to compare results and validate our approach.

The role of complement in inflammation and adaptive immunity.

Major advances in our understanding of the immunobiology of complement were made within the past 5 years primarily due to the development of gene‐targeting technology. New strains of mice bearing specific deficiencies in serum complement proteins or their receptors were developed using this approach. Characterization of these mice has provided new and exciting insights into the biology of the complement system. In this review, we discuss recent results on two important aspects of the complement system, i) host protection and inflammation, and ii) regulation of B lymphocytes of adaptive immunity. While these two roles appear distinct, they are linked. We discuss how natural antibody and classical pathway complement work together in host protection against bacterial infection on the one hand but, on the other, they co‐operate to induce inflammation as observed in reperfusion injury. Significantly, the lymphocytes that produce natural antibody, the B‐1 lymphocytes, are regulated in part by the complement system.

Platelet-released supernatants increase migration and proliferation, and decrease osteogenic differentiation of bone marrow-derived mesenchymal progenitor cells under in vitro conditions

Platelet-rich plasma is currently promoted to serve as an adjuvant for bone grafts to enhance quantity and quality of newly forming bone; however, the underlying cellular mechanisms are not fully understood. We show here that supernatants of leukocyte-depleted thrombin-activated platelets increase migration and proliferation, and decrease osteogenic differentiation of bone marrow-derived mesenchymal progenitor cells under in vitro conditions. Using neutralizing antibodies raised against platelet-derived growth factor (PDGF), the observed effects of platelet-released supernatants were diminished. The mitogenic response was also decreased when extracellular signal-regulated protein kinase (ERK) signalling was inhibited by PD98059; however, PD98059 did not reverse the effects of platelet-released supernatants on migration and osteogenic differentiation. Consistent with an ERK-mediated mitogenic activity, incubation of serum-starved mesenchymal cell progenitors with platelet-released supernatants increased phosphorylation of the kinase. Together, these observations indicate that PDGF is a key factor released upon platelet activation that can increase migration and proliferation, and decreases osteogenic differentiation of mesenchymal progenitor cells under in vitro conditions. The results further suggest that ERK signalling is required to mediate the mitogenic response to platelet-released supernatants.

Analyzing and relating bug report data for feature tracking

Gaining higher level evolutionary information aboutlarge software systems is a key in validating past and adjustingfuture development processes. In this paper, we analyzethe proximity of software features based on modificationand problem report data that capture the systems evolutionhistory. Features are instrumented and tracked, therelationships of modification and problem reports to thesefeatures are established, and the tracked features are visualizedto illustrate their otherwise hidden dependencies.Our approach uncovers these hidden relationships betweenfeatures via problem report analysis and presents them ineasy-to-evaluate visual form. Particular feature dependenciesthen can be selected to assess the feature evolution byzooming in into an arbitrary level of detail. Such visualizationof interwoven features, therefore, can indicate locationsof design erosion in the architectural evolution of asoftware system. Our approach has been validated usingthe large open source software project of Mozilla and itsbug reporting system Bugzilla.

Visualizing multiple evolution metrics

Observing the evolution of very large software systems needs the analysis of large complex data models and visualization of condensed views on the system. For visualization software metrics have been used to compute such condensed views. However, current techniques concentrate on visualizing data of one particular release providing only insufficient support for visualizing data of several releases.In this paper we present the RelVis visualization approach that concentrates on providing integrated condensed graphical views on source code and release history data of up to n releases. Measures of metrics of source code entities and relationships are composed in Kiviat diagrams as annual rings. Diagrams highlight the good and bad times of an entity and facilitate the identification of entities and relationships with critical trends. They represent potential refactoring candidates that should be addressed first before further evolving the system. The paper provides needed background information and evaluation of the approach with a large open source software project.

COMPLEMENT AND THE IMMUNE RESPONSE

This past year has seen a major advance in our understanding of how the complement system enhances the adaptive immune response. The use of in vivo models has revealed that direct coupling of C3d to antigen is sufficient to dramatically reduce the amount of antigen required for a secondary response. At least one important requirement for the enhancing effect was determined to be expression of the CD21 (C3d receptor) on B cells.

Vascular endothelial growth factor C and vascular endothelial growth factor receptor 3 expression in squamous cell carcinomas of the head and neck.

VEGF proteins and their receptors are involved in tumor vessel neoformation. The third VEGF receptor, VEGFR3 (flt‐4) is important during both blood vessel development and lymphatic vessel formation. Because HNSCC preferentially metastasizes to regional lymph nodes, we investigated the expression of VEGFR3 and its ligand VEGF‐C in head and neck squamous cell carcinomas by semiquantitative RT‐PCR (4 HNSCC cells lines and 6 HNSCC specimens) and by immunohistochemistry (18 HNSCC specimens). VEGFR3 protein expression was confirmed by Western blotting in four HNSCC cell lines and six HNSCC specimens.

Improving evolvability through refactoring

Refactoring is one means of improving the structure of existing software. Locations for the application of refactoring are often based on subjective perceptions such as bad smells, which are vague suspicions of design shortcomings. We exploit historical data extracted from repositories such as CVS and focus on change couplings: if some software parts change at the same time very often over several releases, this data can be used to point to candidates for refactoring. We adopt the concept of bad smells and provide additional change smells. Such a smell is hardly visible in the code, but easy to spot when viewing the change history. Our approach enables the detection of such smells allowing an engineer to apply refactoring on these parts of the source code to improve the evolvability of the software. For that, we analyzed the history of a large industrial system for a period of 15 months, proposed spots for refactorings based on change couplings, and performed them with the developers. After observing the system for another 15 months we finally analyzed the effectiveness of our approach. Our results support our hypothesis that the combination of change dependency analysis and refactoring is applicable and effective.

Platelets are mitogenic for periosteum-derived cells

The early stages of bone regeneration are associated with a high mitogenic activity of periosteal cells. Here we addressed the question of whether platelets that accumulate within the developing haematoma can account for this tissue response. Addition of platelets, platelet‐released supernatants, platelet membranes, and microparticles to bovine periosteum‐derived cells resulted in an increase in 3H‐thymidine incorporation; lipid extracts had no effect. Platelet‐released supernatants retained their activity after incubation at 56°C, but not at 100°C. Gel chromatographic analysis revealed the highest mitogenic activity at approximately 35 kD. Of the factors released from activated platelets, basic fibroblast growth factor (bFGF) and platelet‐derived growth factor (PDGF) increased 3H‐thymidine incorporation. The mitogenic activity of platelet‐released supernatants was decreased by anti‐PDGF, and anti‐bFGF antibodies. Platelet‐released supernatants increased the number of proliferating periosteum‐derived cells as determined by the expression pattern of Ki67. Platelet‐released supernatants also resulted in a stimulation of cell proliferation in periosteal explants. These results suggest that platelets have the potential to stimulate the mitogenic response of the periosteum during bone repair.