Intercellular adhesion molecule-1 is an endothelial cell adhesion receptor for Plasmodium falciparum

The primary event in the pathogenesis of severe malaria in Plasmodium falciparum infection is thought to be adherence of trophozoite- and schizont-infected erythrocytes to capillary endothelium, a process called sequestration. Identifying the endothelial molecules used as receptors is an essential step in understanding this disease process. Recent work implicates the membrane glycoprotein CD36 (platelet glycoprotein IV; refs 2-5) and the multi-functional glycoprotein thrombospondin as receptors. Although CD36 has a widespread distribution on microvascular endothelium, it may not be expressed on all capillary beds where sequestration occurs, especially in the brain. The role of thrombospondin in cell adhesion, in vitro or in vivo, is less certain. We have noticed that some parasites bind to human umbilical-vein endothelial cells independently of CD36 or thrombospondin. To screen for alternative receptors, we have developed a novel cell-adhesion assay using transfected COS cells, which confirms that CD36 is a cell-adhesion receptor. In addition, we find that an endothelial-binding line of P. falciparum binds to COS cells transfected with a complementary DNA encoding intercellular adhesion molecule-1. As this molecule is widely distributed on capillaries and is inducible, this finding may be relevant to the pathogenesis of severe malaria.     

T-cell receptor delta-chain can substitute for alpha to form a beta delta heterodimer

Specific monoclonal antibodies have made possible the identification of two T-cell antigen receptor (TCR) heterodimers, alpha beta TCR and gamma delta TCR. Formation of these receptors is largely separated by the preferential pairing of alpha-TCR with beta and gamma-TCR with delta, the sequential rearrangement and expression of the TCR loci during thymic development and the deletion of the delta-loci either prior to or concomitant with alpha-rearrangement in alpha beta TCR cells. Here we show that delta-TCR can substitute for alpha in pairing with beta to form a beta delta heterodimer. This receptor is expressed on the cell surface of the T-leukaemia cell line DND41 as analysed with beta- and delta-specific monoclonal antibodies. We suggest that a variety of factors including, for example, the deletion of the delta-TCR loci, can now be understood as exclusion mechanisms operating to prevent not only the formation of gamma delta receptors, but also of beta delta T-cell receptors, thereby promoting the numerically dominant alpha beta TCR lineage. Nevertheless, some developing T-cells that do not rearrange the alpha-loci may express the beta delta TCR as described here.     

Signal transduction through the CD4 receptor involves the activation of the internal membrane tyrosine-protein kinase p56lck

The CD4 T-cell surface antigen is an integral membrane glycoprotein of relative molecular mass 55,000 which binds class II major histocompatibility complex (MHC) molecules expressed on antigen presenting cells (APCs). It is thought to stabilize physical interactions between T cells and APCs (for a review, see ref. 1). Evidence is accumulating that suggests that CD4 can transduce an independent signal during T-cell activation. It has recently been shown that CD4 expressed on human and murine T cells is physically associated with the Src-related tyrosine protein kinase p56lck (refs 7, 8). These results indicate that CD4 can function as a signal transducer and suggest that tyrosine phosphorylation events may be important in CD4-mediated signalling. Here, we present evidence that cross-linking of the CD4 receptor induces a rapid increase in the tyrosine-specific protein kinase activity of p56lck and is associated with the rapid phosphorylation of one of the subunits (zeta) of the T-cell receptor complex on tyrosine residues. These data provide direct evidence for a specific CD4 signal transduction pathway that is mediated through p56lck and suggest that some of the tyrosine phosphorylation events detected during antigen-mediated T-cell activation may result from signalling through this surface molecule.     

Vesicular removal by oligodendrocytes of membrane attack complexes formed by activated complement

Oligodendrocytes synthesize myelin in the central nervous system and maintain it in lamellar sheaths around axons. Techniques for studying oligodendrocyte development in vitro can be used, indirectly, to investigate the myelin injury that occurs in human and experimental demyelinating disease. Cell-mediated immune mechanisms are necessary but not sufficient to induce myelin damage in vivo; more recently complement has also been implicated in the pathogenesis both of multiple sclerosis and experimental allergic encephalomyelitis. Previously we have demonstrated that antibody-independent complement activation occurs in vitro at the oligodendrocyte surface. Here we show that the ensuing oligodendrocyte injury is reversible, and that recovery involves the release of membrane-attack complex-enriched vesicles from the surface of viable cells. The demonstration of morphologically and immunochemically identical vesicles in the cerebrospinal fluid of patients with multiple sclerosis suggests that reversible complement-mediated injury contributes to myelin damage in vivo.     

A recombinant immunotoxin consisting of two antibody variable domains fused to Pseudomonas exotoxin

Antibodies and growth factors have been chemically coupled to different toxins to produce cytotoxic molecules that selectively kill cells bearing appropriate antigens or receptors. Antibody-toxin conjugates (immunotoxins) produced using conventional chemical coupling techniques have several undesirable characteristics. The smallest binding unit of an antibody is an Fv fragment which consists of a light and heavy chain variable domain. Recently, active single chain Fv fragments of antibodies have been produced in Escherichia coli by attaching the light and heavy chain variable domains together with a peptide linker. Here we describe the construction and expression in E. coli of a single chain antibody toxin fusion protein, anti-Tac(Fv)-PE40, in which the variable regions of anti-Tac, a monoclonal antibody to the p55 subunit of the human interleukin-2 receptor, are joined in peptide linkage to PE40, a modified form of Pseudomonas exotoxin lacking its binding domain. Anti-Tac(Fv)-PE40 was very cytotoxic to two interleukin-2 receptor-bearing human cell lines but was not cytotoxic to receptor-negative cells.     

Three-dimensional crystal structures of Escherichia coli met repressor with and without corepressor

The three-dimensional crystal structure of met repressor, in the presence or absence of bound corepressor (S-adenosylmethionine), shows a dimer of intertwined monomers, which do not have the helix-turn-helix motif characteristic of other bacterial repressor and activator structures. We propose that the interaction of met repressor with DNA occurs through either a pair of symmetry-related alpha-helices or a pair of beta-strands, and suggest a model for binding of several dimers to met operator regions.     

Regulation of the retinal interphotoreceptor matrix Na by the retinal pigment epithelium during the light response

We examined the rabbit retinal pigment epithelium (RPE) for Na transport properties which would allow it to buffer undesirable changes in Na concentrations in the interphotoreceptor matrix (IPM) during light and dark cycles. The RPE is selectivity permeable to sodium. Open and short circuit transport studies with RPE indicate a circulating (choroid to retina and back) Na current which does not compromise the electrical integrity of the blood brain barrier but together with the Na permeselectivity is of sufficient magnitude to buffer both upwards and downwards movements of IPM [Na] during light or dark responses.     

Dissociated cell suspensions ofCarcinus maenas Y-organs as a tool to study ecdysteroid production and its regulation

In vitro ecdysteroid production by dissociated Y-organ cells of the shore crabCarcinus maenas was characterized during short-term incubations. Under optimized conditions (M199 adjusted to crab osmolality and with the addition of 10% foetal calf serum), ecdysteroid production by dispersed cells increased linearly during 4-hour incubations, with little intra-assay variation. 25-deoxyecdysone was mainly produced. PurifiedCarcinus molt inhbiting hormone (CamMIH) produced a dose-dependent inhibition of ecdysteroid production by dispersed cells. The cells were about 50 times more sensitive than whole glands to MIH. Other structurally-related peptides were tested.