The murine t-complex encodes t-complex polypeptide-1 (TCP1), which is constitutively expressed in almost all cells, and upregulated during spermatogenesis. Mammalian sequences have greater than 96% identity with each other, and greater than 60% identity with Drosophila melanogaster and yeast orthologues. TCP1 is essential in yeast, and is postulated to be the cytosolic mammalian equivalent of groEL. We report here that, in the native state, murine and human TCP1 is distributed throughout the cytosol as an 800K-950K hetero-oligomeric particle in association with four to six unidentified proteins and two Hsp70 heat-shock proteins. Negative-stain electron microscopy indicates that the structure is two stacked rings, 12-16 nm in diameter. Therefore, despite similarities with the chaperonin 60 proteins, these data indicate that TCP1 is biochemically and structurally unique. We suggest that TCP1 may represent one of a family of molecules in the eukaryotic cytosol involved in protein folding and regulated in part by their heteromeric associations.

A collaborative study of human transmissible spongiform encephalopathies has been carried out from 1993 to 2000 and includes data from 10 national registries, the majority in Western Europe. In this study, we present analyses of predictors of survival in sporadic (n = 2304), iatrogenic (n = 106) and variant Creutzfeldt-Jakob disease (n = 86) and in cases associated with mutations of the prion protein gene (n = 278), including Gerstmann-Sträussler-Scheinker syndrome (n = 24) and fatal familial insomnia (n = 41). Overall survival for each disease type was assessed by the Kaplan-Meier method and the multivariate analyses by the Cox proportional hazards model. In sporadic disease, longer survival was correlated with younger age at onset of illness, female gender, codon 129 heterozygosity, presence of CSF 14-3-3 protein and type 2a prion protein type. The ability to predict survival based on patient covariates is important for diagnosis and counselling, and the characterization of the survival distributions, in the absence of therapy, will be an important starting point for the assessment of potential therapeutic agents in the future.

Macrophages, granulocytes and many lymphocytes express or secrete receptors for the Fc domain of immunoglobulins (Ig). These Fc receptors (FcRs) are heterogeneous and can be distinguished on the basis of their cellular distribution and specificities for different immunoglobulin isotypes. Although their functions are not completely understood, FcRs are known to be involved in triggering various effector cell functions and in regulating differentiation and development of B-cells. One of the best characterized is the mouse macrophage-lymphocyte receptor for IgG1 and IgG2b (ref. 5). On macrophages, this FcR mediates the endocytosis of antibody-antigen complexes via coated pits and coated vesicles, the phagocytosis of Ig-coated particles, and the release of various inflammatory and cytotoxic agents. It is possible that the receptor possesses an intrinsic ligand-activated ion channel activity responsible for some of these functions. The IgG1/IgG2b FcR has been isolated and shown to be a transmembrane glycoprotein of relative molecular mass (Mr) 47,000-60,000 (47-60 K) containing four N-linked oligosaccharide chains and a large (greater than 10K) cytoplasmic domain. It is also immunologically indistinguishable from the murine Ly-17 alloantigen which, in turn, is tightly linked to the Mls lymphocyte activation locus. Here we describe the isolation and characterisation of a complementary DNA clone encoding the whole of the IgG1/IgG2b FcR expressed by the mouse macrophage-like cell line P388D1. The receptor is a member of the immunoglobulin superfamily and, like Ly-17, maps to the distal portion of chromosome 1. cDNA probes detect one or two mRNA species in FcR+ macrophage and B-cell lines, but not in FcR- cells or a receptor-deficient variant derived from a FcR+ B-cell line. Finally, DNA hybridization analysis indicates the receptor gene is partially deleted or rearranged in the FcR- variant.

Mouse macrophage Fc receptors specific for IgG1/IgG2b mediate the binding and pinocytic uptake of soluble IgG-containing antibody-antigen complexes. Internalization of these multivalent IgG complexes is accompanied not only by the intracellular degradation of the ligand, but also by a net decrease in the number of plasma membrane Fc receptors and an accelerated rate of receptor turnover. In contrast, internalized receptors bound to a monovalent ligand, the high affinity Fab fragment of the antireceptor mAb 2.4G2, escape degradation by rapidly recycling to the cell surface. In this paper, we have characterized the intracellular pathway involved in the endocytosis and transport of Fc receptors in the J774 macrophage cell line. The results show that the uptake of multivalent ligands follows the normal pathway of receptor-mediated endocytosis: internalization in clathrin-coated pits and coated vesicles, delivery to endosomes, and finally to acid hydrolase-rich lysosomes. Immunoprecipitation of radiolabeled receptor from Percoll density gradients showed that endocytosis of the IgG complexes also results in the concomitant transport of the receptor to lysosomes. Although uptake of the monovalent Fab fragment had no detectable effect on intracellular receptor distribution, preparations of 2.4G2 Fab rendered multivalent by adsorption to colloidal gold were as effective as the IgG complexes at causing lysosomal accumulation of internalized receptors. Thus, it is likely that the down-regulation and degradation of Fc receptors which occurs during the endocytosis of antibody-antigen complexes is due to the transport of internalized receptors to lysosomes. Moreover, the ability of certain Fc receptor-bound ligands to interfere with receptor recycling and trigger lysosomal transport seems to depend on ligand valency rather than on the presence or absence of Fc domains on intact IgG molecules.

Paramount among issues relating to the transmissible spongiform encephalopathies (also known as prion diseases) is the absence of any effective therapy. This need has been heightened by the substantial European and emerging global problem of bovine spongiform encephalopathy and consequent variant Creutzfeldt-Jakob disease. Stimulated by the recent reports of a potent antiprion effect in cell culture-based clearance assays, we studied the utility of quinacrine in a well-characterized in vivo model of mouse-adapted transmissible spongiform encephalopathy. Our results failed to show any evidence that quinacrine is effective when using the simple but objective measure of survival prolongation.