Comparative efficiencies of bispecific F(ab′γ)2 and chimeric mouse/human IgG antibodies in recruiting cellular effectors for cytotoxicity via Fcγ receptors

Summary The three forms of Fc receptor carried by monocytes (FcRI, II) and natural killer (NK) cells (FcRIII) are all capable of mediating cell lysis. Here we compare the use of F(ab)₂ bispecific antibodies, specifically targetting individual FcR, and chimeric IgG mouse/human antibodies which are capable of targetting all FcR, for their ability to mediate target cell destruction. The derivatives are prepared by linking hinge sulphydryl residues via tandem thioether bonds, using a bismaleimide crosslinker: Fab from an anti-FcR mAb linked to Fab from a common anti-target mAb (BsAb), or Fab from the common anti-target mouse antibody linked to human Fc (FabFc or bisFabFc). All the derivatives targetting chick red blood cells gave efficient lysis, although different effector cell donors yielded differences in both the lytic levels achieved and the comparative efficiencies of derivatives. In contrast, significant lysis of the guinea pig lymphoblastic leukaemia, L₂C, regularly resulted only via the anti-FcRIII BsAb and the chimeric derivatives. These results suggest that the chimeric, Fc-containing derivatives mediate tumour cell lysis principally through FcRIII on NK cells. This is in contrast to the situation with the chick red blood cells where the chimeric derivatives appear capable of lysing erythrocytes by utilizing either monocytes or NK cells, because significant (50%) lysis occurred with effector cell populations magnetically depleted through either FcRII or FcRIII. A major difference between these two types of antibody derivative was their ability to function in the presence of high concentrations of normal human Fc. The lysis mediated by BsAb reactive with FcRI or II was unaffected by the presence of human Fc at 2.5 mg/ml (a concentration comparable with that yielded by IgG in plasma) whereas the BsAb recognizing FcRIII and all the Fc-containing derivatives were completely inhibited.This work has been supported by Tenovus, the Cancer Research Campaign, the Leukaemia Research Fund, Italfarmaco, Milano, Italy and the Imperial Cancer Research Fund     

The effects of chlorhexidine on the maximum specific growth rate, biomass and hydrolytic enzyme production of Bacteroides gingivalis grown in continuous culture

Bacteroides gingivalis was grown in continuous culture in the presence of chlorhexidine. Maximum specific growth rates and biomass levels initially increased but then decreased as the chlorhexidine level increased from 0 to 30 μg/ml. Total inhibition of growth occurred when the chlorhexidine concentration reached 60 μg/ml. The steady-state levels of cell-bound, extracellular vesicle and extracellular soluble enzymes, trypsin-like protease, alkaline phosphatase and N -acetyl-β-glucosaminidase were measured. With increasing sub-lethal concentrations of chlorhexidine, levels of alkaline phosphatase increased noticeably in all three fractions of culture, whilst cell-bound and extracellular vesicle levels of N -acetyl-β-glucosaminidase remained approximately constant. Extracellular soluble levels of alkaline phosphatase and N -acetyl-β-glucosaminidase increased with increasing levels of chlorhexidine. The levels of trypsin-like protease decreased significantly in all fractions of the culture when cells were grown in the presence of chlorhexidine. Thus, chlorhexidine has a differential effect on the production of B. gingivalis hydrolytic enzymes.     

Evolution of the ATP-binding-cassette transmembrane transporters of vertebrates

The ATP-binding-cassette transmembrane transporters (ABC transporters) known from vertebrates belong to four major subfamilies: (1) the P- glycoproteins (Pgp); (2) the cystic fibrosis transmembrane conductance regulators (CFTR); (3) the Tap proteins encoded with the major histocompatibility complex of mammals; and (4) the peroxisomal membrane proteins. Both Pgp and CFTR have a structure suggesting a past internal gene duplication; a phylogenetic analysis indicated that these duplications occurred independently, while an independent tandem gene duplication occurred in the case of the Tap family. Both the Pgp and Tap proteins show evidence of relationship to bacterial ABC transporters lacking internal duplication, and both are significantly more closely related to the HlyB and MsbA families of transporters from purple bacteria than they are to ABC transporters from nonpurple bacteria. The simplest hypothesis to explain this observation is that eukaryotic Pgp and Tap genes are descended from a mitochondrial gene or genes that were subsequently translocated to the nuclear genome. The Pgp genes of eukaryotes are characterized by a remarkable degree of convergent evolution between the ATP-binding cassettes of their N- terminal and C-terminal halves, whereas no such convergence is seen between the two halves of CFTR genes or between the duplicated Tap genes. Exon 13 of the CFTR gene, which encodes a putative regulatory domain not found in other ABC transporters apart from CFTR, showed high levels of both synonymous and nonsynonymous difference in comparisons among different mammalian species, suggesting that this region is a mutational hot spot.      

Evidence for the presence of β-lactamase inStreptomyces glaucescens and its inhibition by sodium clavulanate

Streptomyces glaucescens is shown to possess -lactamase activity which is inhibitable by clavulanate. This is important in regard to its use as a cloning host for enzymes of \-lactam biosynthesis.     

Host exclusion and coexistence in apparent and direct competition: An application of bifurcation theory.

Recent empirical studies have focused attention on the interplay in multi-host systems of parasite-mediated apparent competition and direct competition between hosts. However, theoretical investigation of such systems has been hindered by the onset of algebraic intractability with the increase in system dimensionality. In this paper we circumvent this problem by using a geometric approach in which arrays of bifurcation maps are constructed, each map being structured by the set of (bifurcation) points in parameter space at which qualitative changes in system behaviour take place. From these maps can be compiled a concise catalogue of the possible modes of system behaviour, enabling an investigation of the interaction of apparent and direct competitive forces to be carried out. Of importance is the identification of those situations where increasing one or both of these competitive forces leads to a change in the stability state. The maps provide an efficient way of determining whether, and, if so, under what conditions, specific modes of behaviour are allowed by the model. Two field phenomena of particular interest, discussed in the paper, are host invasion and dominance reversal resulting from the introduction of the pathogen into a directly competitive system.     

Arginine methylation: the promise of a ‘silver bullet’ for brain tumours?

Despite intense research efforts, our pharmaceutical repertoire against high-grade brain tumours has not been able to increase patient survival for a decade and life expectancy remains at less than 16 months after diagnosis, on average. Inhibitors of protein arginine methyltransferases (PRMTs) have been developed and investigated over the past 15 years and have now entered oncology clinical trials, including for brain tumours. This review collates recent advances in the understanding of the role of PRMTs and arginine methylation in brain tumours. We provide an up-to-date literature review on the mechanisms for PRMT regulation. These include endogenous modulators such as alternative splicing, miRNA, post-translational modifications and PRMT–protein interactions, and synthetic inhibitors. We discuss the relevance of PRMTs in brain tumours with a particular focus on PRMT1, -2, -5 and -8. Finally, we include a future perspective where we discuss possible routes for further research on arginine methylation and on the use of PRMT inhibitors in the context of brain tumours.

     

Three-Dimensional Trabecular Alignment Model

The Shear-slip Mesh Update Method (SSMUM) is being used in flow simulations involving large but regular displacements of one or more boundaries of the computational domain. We follow up the earlier discussion of the method with notes on practical implementation aspects. In order to establish a benchmark problem for this class of flow problems, we define and report results from a two-dimensional viscous flow around a rotating stirrer in a square chamber. The application potential of the method is demonstrated in the context of biomedical design problem, as we perform an analysis of blood flow in a centrifugal left ventricular assist device, or blood pump, which involves a rotating impeller in a non-axisymmetric housing.     

Soothing the Threatened Brain: Leveraging Contact Comfort with Emotionally Focused Therapy

Social relationships are tightly linked to health and well-being. Recent work suggests that social relationships can even serve vital emotion regulation functions by minimizing threat-related neural activity. But relationship distress remains a significant public health problem in North America and elsewhere. A promising approach to helping couples both resolve relationship distress and nurture effective interpersonal functioning is Emotionally Focused Therapy for couples (EFT), a manualized, empirically supported therapy that is strongly focused on repairing adult attachment bonds. We sought to examine a neural index of social emotion regulation as a potential mediator of the effects of EFT. Specifically, we examined the effectiveness of EFT for modifying the social regulation of neural threat responding using an fMRI-based handholding procedure. Results suggest that EFT altered the brain''s representation of threat cues in the presence of a romantic partner. EFT-related changes during stranger handholding were also observed, but stranger effects were dependent upon self-reported relationship quality. EFT also appeared to increase threat-related brain activity in regions associated with self-regulation during the no-handholding condition. These findings provide a critical window into the regulatory mechanisms of close relationships in general and EFT in particular.