Isolation from mouse spleen of cell populations with high specific infectivity for scrapie virus

Periplocin Alleviates Cardiac Remodeling in DOCA-Salt-Induced Heart Failure Rats

Heart failure with preserved ejection fraction (HFpEF) is a common public health problem associated with increased morbidity and long-term mortality. However, effective treatment for HFpEF was not discovered yet. In the present study, we aimed to decipher the effects of Periplocin on DOCA-induced heart failure rats and explore the possible underlying mechanisms. We demonstrated that Periplocin could significantly attenuate cardiac structural remodeling and improve cardiac diastolic function. Of note, Periplocin significantly inhibited the recruitment of inflammatory and immune cells and decreased the expression of serum inflammatory cytokines. Meanwhile, Periplocin had the effect of cardiac glycosides to improve cardiomyocyte contractility and calcium transient amplitude. These findings indicate that Periplocin might be a potential medicine to treat HFpEF in patients.

Phytochemical screening, anti-oxidant activity and in vitro anticancer potential of ethanolic and water leaves extracts of Annona muricata (Graviola)

OBJECTIVE

To determine the phytochemical composition, antioxidant and anticancer activities of ethanolic and water leaves extracts of Annona muricata (A. muricata) from the Eastern Uganda.

METHODS

Phytochemical screening was conducted using standard qualitative methods and a Chi-square goodness of fit test was used to assign the relative abundance of the different phytochemicals. The antioxidant activity was determined using the 2, 2-diphenyl-2-picrylhydrazyl and reducing power methods whereas the in vitro anticancer activity was determined using three different cell lines.

RESULTS

Phytochemical screening of the extracts revealed that they were rich in secondary class metabolite compounds such as alkaloids, saponins, terpenoids, flavonoids, coumarins and lactones, anthraquinones, tannins, cardiac glycosides, phenols and phytosterols. Total phenolics in the water extract were (683.69±0.09) μg/mL gallic acid equivalents (GAE) while it was (372.92±0.15) μg/mL GAE in the ethanolic extract. The reducing power was 216.41 μg/mL in the water extract and 470.51 μg/mL GAE in the ethanolic extract. In vitro antioxidant activity IC50 was 2.0456 mg/mL and 0.9077 mg/mL for ethanolic and water leaves extracts of A. muricata respectively. The ethanolic leaves extract was found to be selectively cytotoxic in vitro to tumor cell lines (EACC, MDA and SKBR3) with IC50 values of 335.85 μg/mL, 248.77 μg/mL, 202.33 μg/mL respectively, while it had no cytotoxic effect on normal spleen cells. The data also showed that water leaves extract of A. muricata had no anticancer effect at all tested concentrations.

CONCLUSIONS

The results showed that A. muricata was a promising new antioxidant and anticancer agent.

The immunobiology of prion diseases

Individuals infected with prions succumb to brain damage, and prion infections continue to be inexorably lethal. However, many crucial steps in prion pathogenesis occur in lymphatic organs and precede invasion of the central nervous system. In the past two decades, a great deal has been learnt concerning the cellular and molecular mechanisms of prion lymphoinvasion. These properties are diagnostically useful and have, for example, facilitated preclinical diagnosis of variant Creutzfeldt-Jakob disease in the tonsils. Moreover, the early colonization of lymphoid organs can be exploited for post-exposure prophylaxis of prion infections. As stromal cells of lymphoid organs are crucial for peripheral prion infection, the dedifferentiation of these cells offers a powerful means of hindering prion spread in infected individuals. In this Review, we discuss the current knowledge of the immunobiology of prions with an emphasis on how basic discoveries might enable translational strategies.

Remodeling of the mononuclear phagocyte network underlies chronic inflammation and disease progression in heart failure: critical importance of the cardiosplenic axis

RATIONALE

The role of mononuclear phagocytes in chronic heart failure (HF) is unknown.

OBJECTIVE

Our aim was to delineate monocyte, macrophage, and dendritic cell trafficking in HF and define the contribution of the spleen to cardiac remodeling.

METHODS AND RESULTS

We evaluated C57Bl/6 mice with chronic HF 8 weeks after coronary ligation. As compared with sham-operated controls, HF mice exhibited: (1) increased proinflammatory CD11b+ F4/80+ CD206- macrophages and CD11b+ F4/80+ Gr-1(hi) monocytes in the heart and peripheral blood, respectively, and reduced CD11b+ F4/80+ Gr-1(hi) monocytes in the spleen; (2) significantly increased CD11c+ B220- classical dendritic cells and CD11c+ low)B220+ plasmacytoid dendritic cells in both the heart and spleen, and increased classic dendritic cells and plasmacytoid dendritic cells in peripheral blood and bone marrow, respectively; (3) increased CD4+ helper and CD8+ cytotoxic T-cells in the spleen; and (4) profound splenic remodeling with abundant white pulp follicles, markedly increased size of the marginal zone and germinal centers, and increased expression of alarmins. Splenectomy in mice with established HF reversed pathological cardiac remodeling and inflammation. Splenocytes adoptively transferred from mice with HF, but not from sham-operated mice, homed to the heart and induced long-term left ventricular dilatation, dysfunction, and fibrosis in naive recipients. Recipient mice also exhibited monocyte activation and splenic remodeling similar to HF mice.

CONCLUSIONS

Activation of mononuclear phagocytes is central to the progression of cardiac remodeling in HF, and heightened antigen processing in the spleen plays a critical role in this process. Splenocytes (presumably splenic monocytes and dendritic cells) promote immune-mediated injurious responses in the failing heart and retain this memory on adoptive transfer.

Plasmacytoid dendritic cells sequester high prion titres at early stages of prion infection

In most transmissible spongiform encephalopathies prions accumulate in the lymphoreticular system (LRS) long before they are detectable in the central nervous system. While a considerable body of evidence showed that B lymphocytes and follicular dendritic cells play a major role in prion colonization of lymphoid organs, the contribution of various other cell types, including antigen-presenting cells, to the accumulation and the spread of prions in the LRS are not well understood. A comprehensive study to compare prion titers of candidate cell types has not been performed to date, mainly due to limitations in the scope of animal bioassays where prohibitively large numbers of mice would be required to obtain sufficiently accurate data. By taking advantage of quantitative in vitro prion determination and magnetic-activated cell sorting, we studied the kinetics of prion accumulation in various splenic cell types at early stages of prion infection. Robust estimates for infectious titers were obtained by statistical modelling using a generalized linear model. Whilst prions were detectable in B and T lymphocytes and in antigen-presenting cells like dendritic cells and macrophages, highest infectious titers were determined in two cell types that have previously not been associated with prion pathogenesis, plasmacytoid dendritic (pDC) and natural killer (NK) cells. At 30 days after infection, NK cells were more than twice, and pDCs about seven-fold, as infectious as lymphocytes respectively. This result was unexpected since, in accordance to previous reports prion protein, an obligate requirement for prion replication, was undetectable in pDCs. This underscores the importance of prion sequestration and dissemination by antigen-presenting cells which are among the first cells of the immune system to encounter pathogens. We furthermore report the first evidence for a release of prions from lymphocytes and DCs of scrapie-infected mice ex vivo, a process that is associated with a release of exosome-like membrane vesicles.

Prion Diseases and the Spleen

Transmissible spongiform encephalopathies are fatal neurodegenerative disorders that include Creutzfeldt-Jakob disease in humans, bovine spongiform encephalopathy and scrapie in sheep and goats. Transmissible spongiform encephalopathies are thought by some to result from changes in the conformation of a membrane glycoprotein called PrPC (prion protein) into a pathogenic form, PrPSc, which constitutes the major component of an unprecedented type of infectious particle supposedly devoid of nucleic acid. Although there is no primary immunological response to the infectious agent, several lines of evidence indicate an involvement of the lymphoreticular system in the development of prion diseases. Studies in rodents have shown that after peripheral infection, uptake of the scrapie agent is followed by an initial phase of replication in the lymphoreticular system, particularly the spleen and lymph nodes. Moreover, infectivity titers in lymphoreticular organs reach a maximum relatively quickly, well before those in the brain, and then maintain a plateau for the remainder of the disease progression. The presence of PrPSc in peripheral lymphoid organs of all cases of variant Creutzfeldt-Jakob disease strongly underscores the importance of the lymphoreticular system. Thus, a better understanding of the cells participating in PrPSc replication and dissemination into the central nervous system is of particular interest. This review will therefore discuss the present knowledge of the role of the spleen in transmissible spongiform encephalopathies as well as the participation of the different spleen cell types in the disease process.

Differential constitutive and activation-dependent expression of prion protein in human peripheral blood leucocytes

The cellular isoform of the prion protein (PrPC) is a cell surface glycoprotein that has recently been shown to play a role in haemopoietic cell activation and proliferation. We have characterized the constitutive expression of PrPC on human peripheral blood (pB) cell populations, using PrP-specific antibodies in a multiparameter flow cytometry approach. We found that T cells, NK cells and monocytes exhibit similar PrPC levels, whereas PrPC surface staining on B cells was significantly lower and was virtually absent on granulocytes. Within the T-cell compartment, CD8+ cells showed a significantly higher PrPC expression than CD4+ cells. Similarly, CD3+ cells co-expressing the activation marker CD56 (N-CAM) exhibited significantly higher PrPC expression levels than their CD56- counterparts. Culture of CD14+ pB monocytes for 12-48 h in the presence of interferon gamma (IFN-gamma) resulted in a significant increase in PrPC expression in a time- and concentration-dependent manner. This effect was partially abrogated by the addition of the metabolic inhibitor cycloheximide, indicating the role of protein synthesis in this process. Our results show that PrPC expression on human haemopoietic cells correlates with the activation and developmental status of these cells, suggesting an important functional role of PrPC in the haemopoietic system.

Prion Protein Expression in Human Leukocyte Differentiation

The cellular isoform of the prion protein (PrPC) is a small glycoprotein attached to the outer leaflet of the plasma membrane by a glycosylphosphatidylinositol anchor. This molecule is involved in the pathogenesis of prion diseases in both humans and animals. We have characterized the expression patterns of PrPC during human leukocyte maturation by flow cytometry with monoclonal antibodies to PrPC, the glycan moiety CD15, and the stem cell marker CD34. We observe that prion protein is present on CD34+bone marrow (BM) stem cells. Although lymphocytes and monocytes maintain PrPC expression throughout their differentiation, PrPC is downregulated upon differentiation along the granulocyte lineage. In vitro retinoic acid–induced differentiation of the premyeloid line HL-60 into granulocyte-like cells mimics the suppression of PrPC in granulocyte differentiation, as both PrPC mRNA and protein are downregulated. These data suggest that selected BM cells and peripheral mononuclear cells may support prion agent replication, because this process is dependent on availability of PrPC. Additionally, retinoic acid–induced extinction of PrPC expression in HL-60 cells provides a potential model to study PrP gene regulation and protein function. Finally, these data suggest the existence of cell-specific glycoforms of PrPC that may determine cellular susceptibility to infection by the prion agent.

Prion Protein Expression in Human Leukocyte Differentiation

The cellular isoform of the prion protein (PrPC) is a small glycoprotein attached to the outer leaflet of the plasma membrane by a glycosylphosphatidylinositol anchor. This molecule is involved in the pathogenesis of prion diseases in both humans and animals. We have characterized the expression patterns of PrPC during human leukocyte maturation by flow cytometry with monoclonal antibodies to PrPC, the glycan moiety CD15, and the stem cell marker CD34. We observe that prion protein is present on CD34+bone marrow (BM) stem cells. Although lymphocytes and monocytes maintain PrPC expression throughout their differentiation, PrPC is downregulated upon differentiation along the granulocyte lineage. In vitro retinoic acid–induced differentiation of the premyeloid line HL-60 into granulocyte-like cells mimics the suppression of PrPC in granulocyte differentiation, as both PrPC mRNA and protein are downregulated. These data suggest that selected BM cells and peripheral mononuclear cells may support prion agent replication, because this process is dependent on availability of PrPC. Additionally, retinoic acid–induced extinction of PrPC expression in HL-60 cells provides a potential model to study PrP gene regulation and protein function. Finally, these data suggest the existence of cell-specific glycoforms of PrPC that may determine cellular susceptibility to infection by the prion agent.

A prion primer

By biological and medical criteria, prions are infectious agents; however, many of their properties differ profoundly from those of conventional microbes. Prions are "encoded" by alterations in protein conformation rather than in nucleic acid or amino acid sequence. New epidemic prion diseases (bovine spongiform encephalopathy and new variant Creutzfeldt-Jakob disease) have recently emerged under the active surveillance of the modern world. The risk of contracting prion disease from blood products or other biologicals is now a focus of worldwide concern. Much has been discovered about prions and prion diseases, but much remains to be done.

The key must fit: macrophages transport prion infection to the central nervous system and may determine the sites of infection within it

It is suggested that the agent for transmissible spongiform encephalopathies is transferred from an original peripheral site of infection into the brain by recruited and selected circulating macrophages/monocytes. It is because of this selection that strains of disease appear to be different when infecting separate species, but retain characteristics when infecting a single species.

Is Creutzfeldt-Jakob disease transmitted in blood?

Creutzfeldt-Jakob disease (CJD) has been considered infectious since the mid-1960s, but its transmissibility through the transfusion of blood or blood products is controversial. The causative agent's novel undefined nature and resistance to standard decontamination, the absence of a screening test, and the recognition that even rare cases of transmission may be unacceptable have led to the revision of policies and procedures worldwide affecting all facets of blood product manufacturing from blood collection to transfusion. We reviewed current evidence that CJD is transmitted through blood.

Interaction of scrapie agent and cells of the lymphoreticular system

The current study focused on the role of lymphoid elements of the lymphoreticular system in scrapie pathogenesis. In the first experiment, adherent and non-adherent splenocytes from mice infected with the 139A scrapie strain were prepared. The level of infectivity on a per cell basis was significantly higher in the adherent cell population. In a second set of experiments, thymocytes, unfractionated splenocytes, T-cell enriched and T-cell depleted fractions of splenocytes were infected in vitro with ME7 scrapie strain. There was no evidence of replication of scrapie in ME7-exposed cells in any of the preparations during the first 5-14 days post-exposure. In assays done 5 days after infection, most of the infectivity was cell-associated. These data suggest that lymphoid cells are not involved in scrapie replication. The level of IgA in the serum of 139A-infected mice was markedly reduced compared to the levels in mice injected with normal mouse brain homogenate or with the ME7 scrapie strain. The reduction in IgA levels in 139A-infected mice was evident at each of the 4 time points tested. The final experiment dealt with the question of scrapie replication in the lymphoreticular organs in mouse strains with different incubation periods for 139A after intraperitoneal injection. The results in this experiment suggest that the difference in incubation periods is related to differences in time of access of infection to the central nervous system rather than to differences in the ability of agent to replicate in spleen.

Abnormal isoform of prion protein accumulates in follicular dendritic cells in mice with Creutzfeldt-Jakob disease

We established that follicular dendritic cells (FDCs) are the site of abnormal prion protein (PrPCJD) accumulations in lymphoid tissues from mice infected with Creutzfeldt-Jakob disease. Evidence of positive FDC staining was observed in Creutzfeldt-Jakob disease-infected mice irrespective of the inoculation route, while no such staining was seen in the control mice. We also found that the severe combined immunodeficiency mouse trait is transmittable via the intracranial route but not via the intraperitoneal route. Mice with severe combined immunodeficiency did not have PrPCJD accumulation in FDCs.

Transmissable spongiform encephalopathy (TSE) agents as crystalline forms of the prion protein (PrP) that multiply by allowing normal metabolic forms of PrP to join the crystal

The prion protein (PrP), is found only in the brain of animals infected with TSE. It is a modified form of a normal protein (PrPn) produced from the genome of the animal. The modification prevents breakdown by proteinases and hence its total chemical or physical structure is unknown. The finding of fibre-like structures in microglia and neurones that cross-react with antibodies produced against PrP and the rapid turnover of PrPn may mean that normal biochemical pathway PrPn forms can join a crystal seed of PrP to produce these fibres. This hypothesis, that the modification of PrP is physical rather than chemical, avoids the major problems with theories of PrP as the infective agent.

Does the infective agent of scrapie replicate without nucleic acid? An assessment

The dogma of a unique status for the scrapie agent falling outside the virological spectrum is critically examined in the light of the circumstances which gave rise to it, and it is concluded that such an extreme view cannot be justified. The dogma arose in the first place by a combination of inadequate methodology and the lack of comparable data from other systems. It has been sustained partly by the same factors, and partly by a general failure to understand the impact on all relevant investigations of the exceptionally tenacious binding of infective agent to host-cell (membrane) components. This has not only greatly distorted the experimental findings, but as a consequence has resulted in extensive data misinterpretation. It is concluded that there is no hard evidence for the absence of a nucleic acid core in the scrapie agent so long as it is accepted that this is very small--i.e., of the order of 30 KDa (kilodaltons)--and is embedded within a cell membrane component matrix which protects it by forming a sequestered microenvironment: further that this is by far the simplest hypothesis.

Cellular isoform of the scrapie agent protein participates in lymphocyte activation

The scrapie agent protein (Sp33-37 or PrPSc) is the disease-associated isoform of a normal cellular membrane protein (Cp33-37 or PrPC) of unknown function. We report that normal human lymphocytes and lymphoid cell lines, but not erythrocytes or granulocytes, express PrPC mRNA and protein. PrPC is detectable on the surface of lymphocytes; the surface immunoreactivity is sensitive to phosphatidylinositol-specific phospholipase C, indicating glycosyl-phosphatidylinositol membrane anchorage. Lymphocyte PrPC surface abundance is increased by cell activation, and polyclonal antibodies to PrPC suppress mitogen-induced activation. We conclude that PrPC is a lymphocyte surface molecule that may participate in cell activation.

Intraperitoneal infection with scrapie is established within minutes of injection and is non-specifically enhanced by a variety of different drugs

Single intraperitoneal (i.p.) doses of 16 different drugs were given to mice 2 h before injecting scrapie i.p. Scrapie was injected as serial ten-fold dilutions of standard inocula and the effective titres obtained were used as a measure of the relative efficiency of infection in treated compared to saline injected mice. Despite the wide variety of drugs tested, most of them increased, non-specifically, the efficiency of infection by 0.6 to 2.1 log10 i.p. LD50 units (i.e., 4 to 126-fold), but only when both drug and scrapie were given i.p. The effect was greatest with a 2 h or a 6 h interval suggesting an involvement either of resident peritoneal cells or of elicited cells such as polymorphonuclear neutrophils. There was no increase in the efficiency of infection after intervals of 2 or 7 days when induced macrophages would predominant. The reverse sequence of injections (scrapie-0.5 h-drug) had no effect despite the persistence of high scrapie titre in the peritoneum at the time of drug injection. However, the effect was restored by a second injection of scrapie in the sequence, scrapie-drug-scrapie. It is concluded that scrapie infection is established within minutes of injection but much of the inoculum is associated with peritoneal cells which are irrelevant to pathogenesis. Drugs may enhance the infection of relevant peritoneal cells or their targeting to the visceral lymphoreticular tissues where early replication takes place.

Attempts to establish the scrapie agent in cell lines

Attempts were made to establish a persistent infection with scrapie agent in four murine cell lines. Of the four lines tested, viz. P388D1, P3-NS1-Ag-1 (NS1), L cells and an NS1 spleen cell hybrid, only the NS1 cell line showed any evidence of agent replication. Ten per cent dimethylsulphoxide (DMSO) was included in the culture media of L cells inoculated with scrapie agent. This treatment raised the initial levels of scrapie agent associating with the L cells but did not result in a persistently infected cell line. An effect of DMSO in the inoculum was observed in mice inoculated intraperitoneally, the incubation period of the disease was considerably shortened.

Pathogenesis of mouse scrapie: distribution of agent in the pulp and stroma of infected spleens

Fourteen spleens were collected from mice infected with the 139A strain of scrapie, at a time when the concentration of agent in spleen was at a plateau. Scrapie infectivity was present in both the pulp and stromal fractions, but the concentration in stroma was about 10 times greater than that in pulp. On average, 1000 pulp cells were required to give 1 LD50 unit of scrapie infectivity. Linear regression analysis of data from 64 mouse spleens showed that the total infectivity correlated with tissue weight (P less than 0.001). The titres of the 14 stromal fractions were significantly correlated with whole spleen weight (P less than 0.02) and with the weight of stroma (P less than 0.02), but not with pulp weight. Hence, the titres in the isolated stroma probably reflect those of the stroma in vivo. In contrast, there was no correlation between total pulp titre and spleen weight, pulp weight or pulp cell number. Moreover, gentle washing of pulp cells removed about 80% of the total infectivity. This suggests that much of the pulp titre is adventitiously associated with cells and is in fact agent released from damaged stroma.

Creutzfeldt-Jakob disease in mice: persistent viremia and preferential replication of virus in low-density lymphocytes

The mode of replication of the "unconventional virus" of Creutzfeldt-Jakob disease was studied in BALB/c mice infected intracerebrally. Virus was detected in the brain, spleen, lung, thymus, liver, kidney, and blood, but not in urine, at various time intervals after inoculation. The highest infectivity was present in the spleen from the second through the ninth weeks postinfection. Density gradient separation of spleen cells with colloidal silica (Percoll) revealed that the highest concentration of virus was present in blastoid cells from lower-density (1.05 to 1.07 g/ml) fractions. These results suggest that blastoid cells play an important role as the initial replication site of virus in the pathogenesis of Creutzfeldt-Jakob disease in mice.

Replication and persistence of measles virus in defined subpopulations of human leukocytes

Replication of Edmonston strain measles virus was studied in several human lymphoblast lines, as well as in defined subpopulations of circulating human leukocytes. It was found that measles virus can productively infect T cells, B cells, and monocytes from human blood. These conclusions were derived from infectious center studies on segregated cell populations, as well as from ultrastructural analyses on cells labeled with specific markers. In contrast, mature polymorphonuclear cells failed to synthesize measles virus nucleocapsids even after infection at a relatively high multiplicity of infection. Measles virus replicated more efficiently in lymphocytes stimulated with mitogens than in unstimulated cells. However, both phytohemagglutinin and pokeweed mitogen had a negligible stimulatory effect on viral synthesis in purified populations of monocytes. In all instances the efficiency of measles virus replication by monocytes was appreciably less than that of mitogenically stimulated lymphocytes or of continuously culture lymphoblasts. Under standard conditions of infection, all of the surveyed lymphoblast lines produced equivalent amounts of measles virus regardless of the major histocompatibility (HL-A) haplotype. Hence, no evidence was found that the HL-A3,7 haplotype conferred either an advantage or disadvantage with respect to measles virus synthesis in an immunologically neutral environment. A persistent infection with measles virus could be established in both T and B lymphoblasts. The release of infectious virus from such persistently infected cells was stable over a period of several weeks and was approximately 100-fold less than peak viral titers obtained in each respective line after acute infection.

Ultrastructural studies of spleens, brains, and brain cell cultures of mice with scrapie

Mouse brains, cell cultures of mouse brains, and spleens from mice with scrapie were examined by electron microscopy. Brains and spleens of 10 scrapie-inoculated and control mice were studied. Seven brain-cell cultures, four of which were from mice inoculated intracerebrally or subcutaneously with scrapie, were examined. Status spongiosus and vacuolated neurons were found in the brains. Structures 35 nm in diameter were seen in the brains of mice inoculated intracerebrally. They were not evident in cell cultures, although a vacuolated structure was found in one such culture. No significant changes were found in the spleens.

Multiplicity of Scrapie virus in infected mouse spleen cells in vivo

Subpopulations of spleen cells from scrapie virus-infected mice were used to determine the average virus content of infected cells in vivo at a time when virus was rapidly increasing in titer in lymphoreticular tissues. Comparison of the mean lethal doses of lysed to intact cells indicated averages of 2 to 6 infectious units per infected cell. In another experiment, preparations of cytoplasmic nucleic acids extracted from spleen cells of infected mice had no detectable infectivity, which suggests that the transmissible form of the virus is not a free nucleic acid.

Transmissible mink encephalopathy: studies on the peripheral lymphocyte

Circulating lymphocytes from mink with transmissible mink encephalopathy were studied for the presence of virus particles and for infectivity. Electron microscope examination of phytohemagglutinin-stimulated lymphocyte cultures revealed no evidence of virus-like particles. Circulating lymphocytes were also found to be noninfectious when the transmissible agent could be demonstrated in intact lymphoid organs in infected mink. A lymphopenia was detected in affected mink during the late clinical stage of disease, but this was most likely a secondary effect due to a terminal stress factor.