The Role of CD40 in the Immune Response

A successful humoral immune response requires reciprocal signaling between T helper cells and B cells. The first signal is antigen specific and is mediated by the interaction between the T cell receptor and antigen in association with major histocompatibility complex on B cells. The subsequent signals are provided by the costimulatory molecules CD40 and CD28 and their respective ligands. CD40L which is expressed on activated T helper cells interacts with CD40 on B cells providing the essential signal for the induction of B cell activation and immunoglobulin production. The importance of the CD40-CD40L interaction has been shown in patients suffering from X-linked immunodeficiency with hyper-IgM (HIGM1). The disease is characterized by the inability of B cells to undergo immunoglobulin isotype switching. Affected males experience recurrent infections and most infections are of bacterial origin, but HIGM1 patients are also unusually susceptible to infections with opportunistic pathogens and often suffer from Pneumocystis carinii pneumonia and Cryptosporidium intestinal infection. Mutations in CD40L molecules are responsible for hyper IgM syndrome in humans. To study the role of the CD40-CD40L interaction in vivo and to derive an animal model for HIGM1, I generated CD40 deficient mice using homologous recombination in embryonic stem (ES) cells. A targeting vector was constructed using an 8 kb CD40 genomic fragment. The G418 resistance gene (NEO) was inserted into the 3rd exon to disrupt the CD40 gene and to allow selection. The targeting vector was transfected into ES cells and G418 resistant clones were isolated - and screened for homologous recombination by Southern blot analysis. Chimaeric mice were generated by injection of targeted ES cell clones into blastocysts. Germline transmission was obtained and heterozygous mutant mice bred to generate CD40 deficient mice. Flow cytometric analysis of lymphocytes in CD40 deficient mice revealed normal development of B and T lymphocytes. CD40 deficient mice were immunized with KLH and assessed for germinal centre formation. CD40 deficient mice did not generate germinal centres. Analysis of serum immunoglobulin levels showed that CD40 deficient mice displayed reduced levels of isotype switched immunoglobulins compared to wild-type mice. These results confirm the crucial role of the CD40-CD40L interaction in humoral immunity. CD40 is also expressed on other antigen presenting cells and the involvement of the CD40-CD40L interaction in cell-mediated immunity was determined in CD40 deficient mice infected with Mycobacterium Bovis (BCG). Although CD40 deficient mice survived mycobacterial infection, the increased numbers of bacilli in spleen and lungs and the reduced production of IFN-ɣ in response to mycobacterial infection indicates that CD40 deficient mice are more susceptible to infection with BCG than control mice

An animal model for the study of pancreatico-biliary and duodenal secretion

A description is given of the surgical preparation of a porcine model for the simultaneous study of the secretory activity of the liver, the pancreas, and the duodenal mucosa. Special emphasis has been given to major and minor complications.The various appllcations of the model are evaluated

BIOMECHANICAL REFLECTIONS ON TEACHING FAST MOTOR SKILLS

Learning to perform a novel movement is believed to require the formation of an internal motor memory model in the central nervous system. This internal model is subsequently used to control the movement, i.e. coordinate muscle generated moments with nonmuscle generated moments in order to execute the intended movement. A substantial part of the non-muscle generated moments acting on each segment in a fast unloaded movement arises due to movement of adjacent segments. If a complex novel movement is taught either in slow motion or by splitting it into partial movements, these intersegmental moments will not be present, and hence not accounted for in the internal motor memory model. It is suggested that coaches take this into account when methods for teaching fast motor skills are considered

Comment on "Penetration of Action Potentials During Collision in the Median and Lateral Giant Axons of Invertebrates"

The action potential (AP) is an electrical impulse elicited by depolarization of the neuronal membrane from the resting membrane potential (around -70  mV). It propagates along the axon, allowing for rapid and distant communication. Recently, it was claimed that two APs traveling in opposite direction will pass unhindered through each other (penetrate) upon collision [Gonzalez-Perez et al.Phys. Rev. X 4, 031047 (2014)PRXHAE2160-330810.1103/PhysRevX.4.031047]. We tested this claim under carefully controlled conditions and found that we cannot reproduce penetration. Instead, APs consistently annihilated upon collision. This is consistent with a vast body of literature

Evaluation of the performance of self-healing concrete at small and large scale under laboratory conditions

HEALCON is an EU-FP7 project which aims to develop self-healing concrete to create durable and sustainable concrete structures. While during the first years of the project the self-healing materials (including the healing agents and suitable encapsulation methodologies) and monitoring techniques were designed and tested at lab-scale, large scale elements have been tested near the end of the project to verify the feasibility and efficiency of the self-healing concrete under conditions closer to reality. For this paper, two types of healing agents were investigated for use in mortar and concrete. The first type of healing agent studied was a coated superabsorbent polymer (C-SAP). It is known that the autogenous healing capacity is increased by incorporation of superabsorbent polymers (SAPs) in mortar/concrete. The agents present in the crack can absorb intruding water, swell and block the crack, leading to immediate sealing, but can also exude moisture to the surrounding concrete environment stimulating healing of the concrete by hydration of unreacted cement particles or by CaCO3 precipitation. The disadvantage of these SAPs in the fresh mortar/concrete mix is however that they absorb large quantities of mixing water, leading to unwanted effects (e.g. loss of workability and macro-pore formation). By coating of the SAPs, we want to eliminate this disadvantage. The fluid bed spraying of the different layers was applied by VTT. A second healing agent studied, is a biogenic healing agent, namely a Mixed Ureolytic Culture (MUC). This type of healing agent was developed by Avecom in order to reduce the cost associated with the production of pure bacterial strains. This mixed ureolytic culture is moreover self-protecting and does not need any further encapsulation. At first, the performance of the healing agents itself was evaluated. For the coated SAPs, the swelling performance and swelling rate were determined, showing that the coating can limit the uptake of water during the first 10-15 minutes. For the MUC, the ureolytic and CaCO3 precipitating capacity was determined, immediately after production of the MUC and after 3 months of storage. The results show the potential of these mixed cultures to be used as self-healing agent in mortar/concrete, but also show a decrease of their effectiveness with time. Subsequently, the healing agents were incorporated in mortar mixes at UGent. A dosage of 1 wt% relative to the cement content caused a large reduction of the mechanical properties of the mortar (up to ~ 50%), except for the coated SAP. The sealing efficiency was evaluated with the water flow test, as designed by one of the project partners in HEALCON. The performance of reference mixes was compared to that of self-healing mixes with SAP, coated SAP or MUC (+ urea). Results showed that for cracks with a width less than 0.150 mm, all mortars were sealed (almost) completely after storage for 28 days in wet-dry environment (12 h wet – 12 h dry) after crack creation. For cracks with a larger width, differences were noticed between the different specimens. Moreover, also the immediate sealing effect induced by the presence of SAPs could be noticed. It has to be noted however that the crack width plays an important role but is varying along the crack length (within a specimen) and between specimens, making the analysis more difficult. In order to extend the application to concrete, self-healing and reference reinforced concrete beams (2500 x 400 x 200 mm) were produced at the Danish Technological Institute. The self-healing concretes contained coated SAPs or MUC. Moreover, the beams were equipped with corrosion sensors that are connected to a wireless monitoring system, developed by the Technology-Transfer- Initiative at the University of Stuttgart. The multi reference electrodes (MuRE) were installed alongside the reinforcements and measure the corrosion potential at certain positions. Data is collected in sufficiently dense intervals by battery powered nodes that transmit the data wirelessly to a base station and further on to a database where it can be accessed through a web based application for data analysis over the internet. At the age of 28 days, three-point bending cracks up to 0.6 mm were created in the beams. Subsequently, the beams were regularly sprayed with water (four times one hour per day) for 6 weeks and afterwards, the beams were, once a week, exposed to 3 wt% NaCl solution for 24 h. Evaluation of the self-healing performance by microscopic analysis (crack microscopy and analysis of thin sections) showed that for the reference beam and beam with MUC no significant healing could be noticed (probably because of insufficient supply of nutrients for the bacteria). For the beams with coated SAPs, the smaller cracks (0.1 and 0.2 mm) were partly closed. Continuous corrosion monitoring showed corrosion in the reference and MUC beams already after the first exposure to NaCl solution. Onset of corrosion was delayed in the case the beams contained coated SAPs