RETICULO-ENDOTHELIAL FUNCTION IN THYMECTOMIZED RATS.
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A form of runt disease has been produced in neonatal CF-1 and ICR mice by the repeated injection of 10(9) washed, autoclaved, saline-suspended staphylococci or streptococci. The most severely affected animals showed a marked decrease in lymphoid tissues and resembled grossly and microscopically animals suffering from the classical runt or wasting disease described by others. The timing of the initial antigenic stimulation was of importance, and animals started on their course of injections at an age of 48 hours or older showed no effect. There was a considerable variation in the severity of the disease within litters and from one litter to another. This variation could not be ascribed to a difference in susceptibility between sexes, since both male and female mice were observed to runt under appropriate conditions. Germ-free ICR mice were much more resistant to the runting phenomenon than conventional animals of the same strain, but could be induced to runt by injection of the staphylococcal vaccine suspended in homologous antiserum. The relationship of the runting phenomenon described here and classical runt disease or runting by adrenal hormones is discussed.
1. Adult (A x C(57)Bl/1)F(1) hybrids regularly show runt disease when injected with adult spleen cells from A strain donors. This also occurs when A strain spleen cells are administered to adult C(3)H mice made tolerant of A strain tissue in the neonatal period. 2. Mice undergoing the graft versus host reaction fail to form antibodies to an intraperitoneal challenge of T(2) bacteriophage. This phenomenon was observed well before any of the other overt signs of runting had occurred. Further, inhibition of antibody production to T(2) phage by graft versus host reaction initiated at an interval following antigenic stimulation is demonstrated. 3. The basis for the immunologic incompetence of the host with respect to T(2) phage is presumed to be the attack of immunologically competent donor cells on the lymphoid cells of the recipient. 4. The failure of the injected parent strain cells to respond to the antigen used may imply immunologic commitment of these cells.
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The NMR structure of the recombinant elk prion protein (ePrP), which represents the cellular isoform (ePrPC) in the healthy organism, is described here. As anticipated from the highly conserved amino acid sequence, ePrPC has the same global fold as other mammalian prion proteins (PrPs), with a flexibly disordered "tail" of residues 23-124 and a globular domain 125-226 with three alpha-helices and a short antiparallel beta-sheet. However, ePrPC shows a striking local structure variation when compared with most other mammalian PrPs, in particular human, bovine, and mouse PrPC. A loop of residues 166-175, which links the beta-sheet with the alpha2-helix and is part of a hypothetical "protein X" epitope, is outstandingly well defined, whereas this loop is disordered in the other species. Based on NMR structure determinations of two mouse PrP variants, mPrP[N174T] and mPrP[S170N,N174T], this study shows that the structured loop in ePrPC relates to these two local amino acid exchanges, so that mPrP[S170N,N174T] exactly mimics ePrPC. These results are evaluated in the context of recent reports on chronic wasting disease (CWD) in captive and free-ranging deer and elk in the U.S. and Canada, and an animal model is proposed for support of future research on CWD.
Transmissible spongiform encephalopathies (TSE) are fatal neurodegenerative diseases of man and animals and are transmitted by a filterable pathogen whose identity is currently unresolved. Our data indicates that Spiroplasma, a wall-less bacterium, is involved in the pathogenesis of TSE. We searched for Spiroplasma ribosomal gene sequences in 10 scrapie-infected sheep brains and 10 normal sheep brains, 7 cervid samples infected with chronic wasting disease (CWD), and 7 normal cervid brains. DNA was extracted from these tissue samples and amplified by polymerase chain reaction (PCR) using primers specific for Spiroplasma-specific 16S rDNA. Specificity of the amplicon was determined by Southern blotting and DNA sequence analyses. Spiroplasma 16S rDNA was found in 8 of 10 scrapie-infected sheep brains and 6 of 7 CWD-infected tissue samples. All normal animal brain samples were negative. Spiroplasma 16S rDNA was also found in two human Creutzfeldt-Jakob diseased (CJD) brains but not in two age-matched normal human brains. DNA sequence analyses of the amplified PCR products from human and animal TSE cases revealed greater than 99% nucleotide sequence homology with Spiroplasma mirum. The presence of Spiroplasma DNA in TSE-infected tissues supports our hypothesis that Spiroplasma may be involved in the pathogenesis of these diseases.
A wasting disease characterized by progressive weight loss and dyspnea has been observed in weaning pigs on a farm in Yamagata Prefecture in 1998. Histopathologic findings in an affected pig were bronchointerstitial pneumonia and intracytoplasmic clusters of basophilic inclusions in macrophages of lymph nodes, which were similar to those in pigs with postweaning multisystemic wasting syndrome (PMWS) recently reported in North America and Europe. Porcine circovirus (PCV)-like particles were observed in bronchial lymph node of the pig by electron microscopy, and PCV antigens were detected in the lesions by immunohistochemical staining. PCV DNA was also detected in the lung and tonsil by PCR, and restriction fragment length polymorphism analysis of the PCR products with HinfI showed the same type of the PCV associated with PMWS (pmws PCV). Homology of nucleotide sequences between the PCR product and corresponding regions of published pmws PCV genomes was very high. These results indicated that virus detected in this study was pmws PCV. To our knowledge, this is the first report on the presence of pmws PCV in Japan.
A comparative serologic and virologic study was performed in pigs from 5 herds with postweaning multisystemic wasting syndrome (PMWS) and 2 herds without PMWS in Quebec. In each herd, 60 blood samples were collected at 4-wk intervals from pigs from 3 to 23 wk of age. The serum was evaluated for the presence of antibodies to porcine circovirus type 2 (PCV2) and porcine reproductive and respiratory syndrome virus (PRRSV), as well as for the presence of nucleic acid of PCV2, PRRSV, an porcine parvovirus (PPV), by means of the polymerase chain reaction (PCR). Serologic profiles for PCV2 were very similar in 6 of the 7 herds, including the 2 without PMWS, and were characterized by a gradual decrease in antibody titres from 3 until 11 wk of age, followed by seroconversion at 15 wk, and high PCV2 antibody titres thereafter in all pigs. Only starting at 11 to 15 wk of age could PCV2 viremia be detected, except in 1 herd, in which clinical signs were observed at 6 to 7 wk of age. A PCV2 viremia could be detected within the same pigs for a minimum of 8 wk, and the virus could still be detected in 41% of the serum samples obtained at 23 wk of age. The antibody level did not appear to influence the occurrence of disease, since titres were similar in pigs in the herds with or without PMWS. Infection with PRRSV, as demonstrated by PCR and seroconversion, preceded that of PCV2 by at least 1 mo in both types of herd. Both PRRSV and PCV2 were detected in some pigs in 5 of the 7 herds, including 1 herd without PMWS. Porcine parvovirus could be detected in serum by PCR in 2 herds with PMWS after the onset of clinical signs and also in 1 herd without PMWS. Genomic analysis of PCV2 strains identified in the herds without PMWS indicated complete or very high homology (99.4% to 100%) with the PCV2 strains identified in 4 herds with PMWS. In our field study, the triggering of PMWS in the herds could not be linked to coinfection with either PRRSV or PPV or to the use of a specific immunostimulant, such as vaccines, or to particular genomic differences between the PCV2 strains identified.
PMWS is a new emerging disease in swine herds worldwide. Field isolates of PCV-2, a putative major causative agent of PMWS, were isolated and genetically characterized. Viral genome of two field isolates (PC201DJ and PC201SS) from pigs showing typical PMWS was sequenced. The nucleotide sequence homology with other PCV-2 isolates was ranging from 95% to 99% in complete viral genomic sequence. The highly conserved nonanucleotide motif of replication origin was identical to that of other PCV-2 isolates. To determine the genetic heterogeneity of PCV-2 isolates, the phylogenetic tree based on the complete genome of PCV-2 isolates were constructed. Two PCV-2 field isolates were closely related to Canadian isolates of PCV-2. PCV-2 isolated from field may have an origin of North America and is possibly originated from importation of breeding stocks. The result indicates that although the genome of PCV-2 is relatively stable in general, minor genetic variations exist among PCV-2 isolates from the different geographic locations. These differences of viral genome might have an important implication for genetic characteristics of PCV-2 infection. Three major immunorelevant epitopes of capsid protein showed variations in amino acid sequences. Also, the variance of amino acid sequence in antigenic epitope existed between two Korean PCV-2 isolates.
The human epithelial sodium channel (hENaC) mediates Na+ transport across the apical membrane of epithelia, and mutations in hENaC result in hypertensive and salt-wasting diseases. In heterologous expression systems, maximal hENaC function requires co-expression of three homologous proteins, the alpha, beta, and gammahENaC subunits, suggesting that hENaC subunits interact to form a multimeric channel complex. Using a co-immunoprecipitation assay, we found that hENaC subunits associated tightly to form homo- and heteromeric complexes and that the association between subunits occurred early in channel biosynthesis. Deletion analysis of gammahENaC revealed that the N terminus was sufficient but not necessary for co-precipitation of alphahENaC, and that both the N terminus and the second transmembrane segment (M2) were required for gamma subunit function. The biochemical studies were supported by functional studies. Co-expression of gamma subunits lacking M2 with full-length hENaC subunits revealed an inhibitory effect on hENaC channel function that appeared to be mediated by the cytoplasmic N terminus of gamma, and was consistent with the assembly of nonfunctional subunits into the channel complex. We conclude that the N terminus of gammahENaC is involved in channel assembly.
The epithelial sodium channel (ENaC) present in the kidney collecting duct, distal colon, and the lung is responsible for salt reabsorption and whole body volume regulation. It is composed of three homologous subunits, alpha, beta, and gamma, and mutations to these subunits can lead to the salt wasting disease pseudohypoaldosteronism type I, associated with decreased channel density at the plasma membrane or to the hypertensive disorder, Liddle's syndrome, in which channel residency time at the plasma membrane is enhanced. Regulation of ENaC trafficking and turnover is therefore critical to sodium homeostasis. In this study we examined whether ENaC is present in the cholesterol-enriched microdomains commonly called lipid rafts, in the endogenously expressing A6 cell line. We demonstrate that a fraction of alpha, beta, and gamma ENaC is present in detergent-insoluble membranes, that subunits exist in membranes that float on discontinuous sucrose density gradients, and that methyl-beta-cyclodextrin treatment causes a redistribution of ENaC subunits to higher density membranes. Furthermore, chronic aldosterone stimulation results in a shift in the membrane density of all three subunits. Biotinylation of apical membrane proteins revealed that ENaC is present in lipid rafts on the plasma membrane. In conclusion, these results show that ENaC is present in lipid rafts both intracellularly and on the cell surface. Raft association may be important for trafficking and/or function of the channel.