Manipulation of Host Cell Organelles by Intracellular Pathogens

Pathogenic intracellular bacteria, parasites and viruses have evolved sophisticated mechanisms to manipulate mammalian host cells to serve as niches for persistence and proliferation. The intracellular lifestyles of pathogens involve the manipulation of membrane-bound organellar compartments of host cells. In this review, we described how normal structural organization and cellular functions of endosomes, endoplasmic reticulum, Golgi apparatus, mitochondria, or lipid droplets are targeted by microbial virulence mechanisms. We focus on the specific interactions of Salmonella, Legionella pneumophila, Rickettsia rickettsii, Chlamydia spp. and Mycobacterium tuberculosis representing intracellular bacterial pathogens, and of Plasmodium spp. and Toxoplasma gondii representing intracellular parasites. The replication strategies of various viruses, i.e., Influenza A virus, Poliovirus, Brome mosaic virus, Epstein-Barr Virus, Hepatitis C virus, severe acute respiratory syndrome virus (SARS), Dengue virus, Zika virus, and others are presented with focus on the specific manipulation of the organelle compartments. We compare the specific features of intracellular lifestyle and replication cycles, and highlight the communalities in mechanisms of manipulation deployed.

Iron Transport across Symbiotic Membranes of Nitrogen-Fixing Legumes

Iron is an essential nutrient for the legume-rhizobia symbiosis and nitrogen-fixing bacteroids within root nodules of legumes have a very high demand for the metal. Within the infected cells of nodules, the bacteroids are surrounded by a plant membrane to form an organelle-like structure called the symbiosome. In this review, we focus on how iron is transported across the symbiosome membrane and accessed by the bacteroids.

Structural characterization of the cell division cycle in Strigomonas culicis, an endosymbiont-bearing trypanosomatid

Strigomonas culicis (previously referred to as Blastocrithidia culicis) is a monoxenic trypanosomatid harboring a symbiotic bacterium, which maintains an obligatory relationship with the host protozoan. Investigations of the cell cycle in symbiont harboring trypanosomatids suggest that the bacterium divides in coordination with other host cell structures, particularly the nucleus. In this study we used light and electron microscopy followed by three-dimensional reconstruction to characterize the symbiont division during the cell cycle of S. culicis. We observed that during this process, the symbiotic bacterium presents different forms and is found at different positions in relationship to the host cell structures. At the G1/S phase of the protozoan cell cycle, the endosymbiont exhibits a constricted form that appears to elongate, resulting in the bacterium division, which occurs before kinetoplast and nucleus segregation. During cytokinesis, the symbionts are positioned close to each nucleus to ensure that each daughter cell will inherit a single copy of the bacterium. These observations indicated that the association of the bacterium with the protozoan nucleus coordinates the cell cycle in both organisms.

Mast cell/IL-4 control of Francisella tularensis replication and host cell death is associated with increased ATP production and phagosomal acidification

Mast cells are now recognized as effective modulators of innate immunity. We recently reported that mast cells and secreted interleukin-4 (IL-4) effectively control intramacrophage replication of Francisella tularensis Live Vaccine Strain (LVS), and that mice deficient in mast cells or IL-4 receptor (IL-4R(-/-)) exhibit greater susceptibility to pulmonary challenge. In this study, we further evaluated the mechanism(s) by which mast cells/IL-4 control intramacrophage bacterial replication and host cell death, and found that IL-4R(-/-) mice exhibited significantly greater induction of active caspase-3 within lung macrophages than wild-type animals following intranasal challenge with either LVS or the human virulent type A strain SCHU S4. Treatment of LVS-infected bone-marrow-derived macrophages with a pancaspase inhibitor (zVAD) did not alter bacterial replication, but minimized active caspase-3 and other markers (Annexin V and propidium iodide) of cell death, whereas treatment with both rIL-4 and zVAD resulted in concomitant reduction of both parameters, suggesting that inhibition of bacterial replication by IL-4 was independent of caspase activation. Interestingly, IL-4-treated infected macrophages exhibited significantly increased ATP production and phagolysosomal acidification, as well as enhanced mannose receptor upregulation and increased internalization with acidification, which correlated with observations in mast cell-macrophage co-cultures, with resultant decreases in F. tularensis replication.

Intracellular demography and the dynamics of Salmonella enterica infections

An understanding of within-host dynamics of pathogen interactions with eukaryotic cells can shape the development of effective preventive measures and drug regimes. Such investigations have been hampered by the difficulty of identifying and observing directly, within live tissues, the multiple key variables that underlay infection processes. Fluorescence microscopy data on intracellular distributions of Salmonella enterica serovar Typhimurium (S. Typhimurium) show that, while the number of infected cells increases with time, the distribution of bacteria between cells is stationary (though highly skewed). Here, we report a simple model framework for the intensity of intracellular infection that links the quasi-stationary distribution of bacteria to bacterial and cellular demography. This enables us to reject the hypothesis that the skewed distribution is generated by intrinsic cellular heterogeneities, and to derive specific predictions on the within-cell dynamics of Salmonella division and host-cell lysis. For within-cell pathogens in general, we show that within-cell dynamics have implications across pathogen dynamics, evolution, and control, and we develop novel generic guidelines for the design of antibacterial combination therapies and the management of antibiotic resistance.

Modeling of infection shows that heterogeneities in bacterial burden per host cell need not be explained by differences in host cell permissiveness; this has important implications for understanding the ecology of infection.

An ultrastructural study of development and reproduction in the nematode parasite Myzocytiopsis vermicola

An isolate of Myzocytiopsis vermicola, a holocarpic parasite of Rhabditis nematodes, was studied with transmission electron microscopy (TEM) to follow development during infection, asexual and sexual reproduction. Nematodes became infected after attachment of apical cystospore buds to the nematode cuticle. Apical buds were packed with vesicles with dense fibrillar contents, which were absent from the thallus. Some thalli developed into sporangia while others became paired gametangial cells. Zoospore cleavage was often intrasporangial, although during the early stages of an epidemic partially differentiated zoospores usually were released via an exit tube into a fine vesicle. Packets of tripartite tubular hairs (TTH) were not observed in the cytoplasm of either developing or mature sporangia. TEM of sectioned material and whole mounts of zoospores revealed biflagellate zoospores, some without hairs and others with a proximal row of very short hairs on the anterior flagellum. Gametangial contact was via a short, walled fertilization tube and surplus antheridial and oogonial nuclei remained in their respective gametangial cells until disintegration of the periplasm. The mature oospores had a scalloped, electron opaque, epispore wall layer. These observations will be discussed in relation to the likely phylogenetic position of the Myzocytiopsidales within the oomycetes.

Organelle identity and the signposts for membrane traffic

Eukaryotic cells have systems of internal organelles to synthesize lipids and membrane proteins, to release secreted proteins, to take up nutrients and to degrade membrane-bound and internalized molecules. Proteins and lipids move from organelle to organelle using transport vesicles. The accuracy of this traffic depends upon organelles being correctly recognized. In general, organelles are identified by the activated GTPases and specific lipid species that they display. These short-lived determinants provide organelles with an identity that is both unique and flexible. Recent studies have helped to establish how cells maintain and restrict these determinants and explain how this system is exploited by invading pathogens.

[Changes and distribution of ATPase activity in the paranodules of Nicotiana tabacum]

Lead phosphate deposition technique was used to investigate the changes and characteristic distribution of ATPase activity in the paranodules of tabacoo. We found that ATPase activity was closely associated with cell type and cell developmental state, thus it was different in various cells and rhizobia. No lead phosphate granules were located in the menstematic cells, although there were a small number of lead phosphate granules in the cytoplasm and organelles of the cells without rhizobia, they did not exist in the young and mature rhizobia. On the contrary, upon the senscence of the cells and rhizobia, a large number of lead phosphate granules appeared on the plasmalemmas and in the cell walls and the inside surfaces of the rhizobia. When the cells and rhizobia progressively senesced, lead phosphate granules increased in number, and they were widely distributed on the tonoplasts, plasmalemmas, cell walls, intercellular layers and in the intercellular spaces. At the same time, they also appeared on the surfaces and in the cytoplasm and nucleoids of the rhizobia. Due to cell disintegration, lead phosphategranules obviously decreased in number, they were only located on the plasmalemmas and membrane-vesicular structures which came from disintegrated organelles.

Aspergillus fumigatus conidia survive and germinate in acidic organelles of A549 epithelial cells

Aspergillus fumigatus is an environmental mould that can cause invasive disease in the immunocompromised host. Previous work has shown that conidia can be internalized by lung epithelial cells (A549) and murine macrophages (J774) in vitro. Therefore, the purpose of this study was to determine the fate of A. fumigatus conidia within the endosomal network of these cells. Co-localization of conidia expressing green fluorescent protein with proteins present in the early endosomal (CD71) and lysosomal (CD63, LAMP-1) membrane was assessed using confocal microscopy. In J774 cells, 75% of internalized conidia were found in phagosomes containing LAMP-1 120 minutes post-infection. In A549 cells, 55% and 58% of internalized conidia were found to co-localize with LAMP-1 and CD63 by 24 hours. Cathepsin D also co-localized with internalized conidia in A549 cells. Phagosomes containing conidia were shown to be acidified in both cell types. Less than 1% of the initial inoculum survived in J774 cells by 12 hours post-infection. After 24 hours, 3% of internalized conidia survived in A549 cells and 34% of these had germinated. By 36 hours, the germlings were able to escape the phagosome and form extracellular hyphae without lysis of the host cell.

Mesosomes and scientific methodology

In his recent article, Nicolas Rasmussen (2001) is harshly critical of what he terms 'empirical philosophy of science', a philosophy that takes seriously the history of science in advancing philosophical pronouncements about science. He motivates his criticism by reflecting on recent history in microbiology involving the 'discovery' of a new bacterial organelle, the mesosome, during the 1950's and 1960's, and the subsequent retraction of this discovery by experimental microbiologists during the late 1970's and early 1980's. In particular, he argues that there was a lack of constancy in the methods microbiologists used in approaching the issue of the existence of mesosomes, and that in fact a similar sort of 'methodological flux' pervades all experimental work. My goal here is to refute Rasmussen's doctrine of flux, and in turn to re-establish order in our understanding of the methods and strategies of experimenters. My strategy in achieving this goal is to re-visit the same crucial research articles in the history of the mesosome episode that Rasmussen (2001) visits; and what I find upon returning to this literature is not flux, as Rasmussen seems to find, but a constancy of method in experimental reasoning, a constancy codified by what I call 'reliable process reasoning'.

Mycobacteria-containing phagosomes associate less annexins I, VI, VII and XI, but not II, concomitantly with a diminished phagolysosomal fusion

We have studied the intracellular localization of annexins I,II, VI, VII, and XI in cells containing latex beads or Mycobacterium avium at different times after ingestion in order to establish whether a correlation existed between the association of annexins to phagosomes and phagolysosomal fusion, since the intracellular survival of mycobacteria is linked to an impairment of phagosome maturation. We demonstrate an important decrease in the levels of association of annexins I, VI, VII and XI, but not II to phagosomes containing either live or killed mycobacteria compared with phagosomes containing inert latex particles. The reduced association of annexins observed was detected only on M. avium-containing phagosomes and not in other cell membrane nor in cytosolic fractions from infected cells, and was apparent from 8 hours through to 4 days after phagocytosis. These findings add elements to the present knowledge of the phagosomal modifications that accompany the survival of intracellular pathogens, suggesting that annexins I, VI, VII, and XI play a secondary role in phagosomal fusion events while annexin II does not seem to be related to the mechanism of regulation of endolysosomal fusion.

Rab5a GTPase regulates fusion between pathogen-containing phagosomes and cytoplasmic organelles in human neutrophils

Biogenesis of phagolysosomes proceeds through a sequential series of interactions with endocytic organelles, a process known to be regulated by Rab and SNARE proteins. The molecular mechanisms underlying phagosome maturation in neutrophils are, however, not clearly understood. We investigated fusion between phagosomes containing the intracellular pathogen Mycobacterium tuberculosis versus the extracellular pathogen Staphylococcus aureus (designated MCP for mycobacteria-containing phagosome and SCP for S. aureus-containing phagosome) and cytoplasmic compartments in human neutrophils. Western blot analysis of phagosomes isolated after internalisation revealed that lactoferrin (a constituent of secondary granules) and LAMP-1 were incorporated into both SCP and MCP, whereas hck(marker of azurophil granules) interacted solely with SCP. The subcellular distribution of the proteins Rab5a and syntaxin-4 suggested a role in docking of granules and/or endosomes to the target membrane in the neutrophil. We observed that during phagocytosis, Rab5a in GTP-bound form interacted with syntaxin-4 on the membrane of MCP and were retained for up to 90 minutes,whereas the complex was recruited to the SCP within 5 minutes but was selectively depleted from these vacuoles after 30 minutes of phagocytosis. Downregulation of Rab5a by antisense oligonucleotides efficiently reduced the synthesis of Rab5a, the binding of syntaxin-4 to MCP and SCP and the capacity for fusion exhibited by the pathogen-containing phagosomes, but it had no effect on bacteria internalisation. These data indicate that the difference in granule fusion is correlated with a difference in the association of Rab5a and syntaxin-4 with the phagosomes. Intracellular pathogen-containing phagosomes retain Rab5a and syntaxin-4, whereas extracellular pathogen-containing phagosomes bind briefly to this complex. These results also identified Rab5a as a key regulator of phagolysosome maturation in human neutrophils.

The Dot/lcm transporter of Legionella pneumophila: a bacterial conductor of vesicle trafficking that orchestrates the establishment of a replicative organelle in eukaryotic hosts

Legionella pneumophila are gram negative bacteria that parasitize professional phagocytes. When ingested by their eukaryotic hosts, these bacteria have the unique ability to alter maturation of the endocytic vacuoles in which they reside initially and create an organelle that supports replication. This review will focus on several scientific breakthroughs made recently that shed light on the mechanisms by which L. pneumophila are able to establish a niche permissive for intracellular growth.

Identification of Icm protein complexes that play distinct roles in the biogenesis of an organelle permissive for Legionella pneumophila intracellular growth

Legionella pneumophila is a bacterial pathogen that can enter the human lung and grow inside alveolar macrophages. To grow within phagocytic host cells, the bacteria must create a specialized organelle that restricts fusion with lysosomes. Biogenesis of this replicative organelle is controlled by 24 dot and icm genes, which encode a type IV-related transport apparatus. To understand how this transporter functions, isogenic L. pneumophila dot and icm mutants were characterized, and three distinct phenotypic categories were identified. Our data show that, in addition to genes that encode the core Dot/Icm transport apparatus, subsets of genes are required for pore formation and modulation of phagosome trafficking. To understand activities required for virulence at a molecular level, we investigated protein-protein interactions. Specific interactions between different Icm proteins were detected by yeast two-hybrid and gel overlay analysis. These data support a model in which the IcmQ-IcmR complex regulates the formation of a translocation channel that delivers proteins into host cells, and the IcmS-IcmW complex is required for export of virulence determinants that modulate phagosome trafficking.

Identification and subcellular localization of the Legionella pneumophila IcmX protein: a factor essential for establishment of a replicative organelle in eukaryotic host cells

The gram-negative respiratory pathogen Legionella pneumophila infects and grows within mammalian macrophages and protozoan host cells. Upon uptake into macrophages, L. pneumophila establishes a replicative organelle that avoids fusion with endocytic vesicles. There are 24 dot/icm genes on the L. pneumophila chromosome required for biogenesis of this vacuole. Many of the Dot/Icm proteins are predicted to be components of a membrane-bound secretion apparatus similar to type IV conjugal transfer systems. We have been investigating the function of L. pneumophila dot/icm gene products that do not have obvious orthologs in other type IV transfer systems, since these determinants could govern processes unique to phagosome biogenesis. The icmX gene product falls into this category. To understand the role of the IcmX protein in pathogenesis, we have detailed interactions between an L. pneumophila icmX deletion mutant and murine bone marrow-derived macrophages. These data demonstrate that icmX is required for biogenesis of the L. pneumophila replicative organelle. Immunoblot analysis indicates that the icmX gene product is a polypeptide with an estimated molecular mass of 50 kDa. The IcmX protein was localized to the bacterial periplasm, and periplasmic translocation was mediated by an N-terminal sec-dependent leader peptide. A truncated IcmX product was secreted into culture supernatants by wild-type L. pneumophila growing extracellularly in liquid media; however, transport of the IcmX protein into eukaryotic host cells was not detected. Proteins similar in molecular weight to IcmX were identified in other Legionella species by immunoblot analysis using a monoclonal antibody specific for L. pneumophila IcmX protein. From these data, we conclude that the IcmX protein is an essential component of the dot/icm secretion apparatus, and that a conserved mechanism of host cell parasitism exists for members of the Legionellaceae family.

Regulation of the macrophage vacuolar ATPase and phagosome-lysosome fusion by Histoplasma capsulatum

Histoplasma capsulatum (Hc) maintains a phagosomal pH of about 6.5. This strategy allows Hc to obtain iron from transferrin, and minimize the activity of macrophage (Mo) lysosomal hydrolases. To determine the mechanism of pH regulation, we evaluated the function of the vacuolar ATPase (V-ATPase) in RAW264.7 Mo infected with Hc yeast or the nonpathogenic yeast Saccharomyces cerevisae (Sc). Incubation of Hc-infected Mo with bafilomycin, an inhibitor of the V-ATPase, did not affect the intracellular growth of Hc, nor did it affect the intraphagosomal pH. In contrast, upon addition of bafilomycin, phagosomes containing Sc rapidly changed their pH from 5 to 7. Hc-containing phagosomes had 5-fold less V-ATPase than Sc-containing phagosomes as quantified by immunoelectron microscopy. Furthermore, Hc-containing phagosomes inhibited phagolysosomal fusion as quantified by the presence of acid phosphatase, accumulation of LAMP2, and fusion with rhodamine B-isothiocyanate-labeled dextran-loaded lysosomes. Finally, in Hc-containing phagosomes, uptake of ferritin was equivalent to phagosomes containing Sc, indicating that Hc-containing phagosomes have full access to the early "bulk flow" endocytic pathway. Thus, Hc yeasts inhibit phagolysosomal fusion, inhibit accumulation of the V-ATPase in the phagosome, and actively acidify the phagosomal pH to 6.5 as part of their strategy to survive in Mo phagosomes.

Interaction of Bartonella henselae with endothelial cells results in bacterial aggregation on the cell surface and the subsequent engulfment and internalisation of the bacterial aggregate by a unique structure, the invasome

Vascular colonisation by Bartonella henselae may cause vaso-proliferative tumour growth with clumps of bacteria found in close association with proliferating endothelial cells. By using B. henselae-infected human umbilical vein endothelial cells as an in vitro model for endothelial colonisation, we report here on a novel mechanism of cellular invasion by bacteria. First, the leading lamella of endothelial cells establishes cellular contact to sedimented bacteria and mediates bacterial aggregation by rearward transport on the cell surface. Subsequently, the formed bacterial aggregate is engulfed and internalised by a unique host cellular structure, the invasome. Completion of this sequence of events requires 24 hours. Cortical F-actin, intercellular adhesion molecule-1 and phosphotyrosine are highly enriched in the membrane protrusions entrapping the bacterial aggregate. Actin stress fibres, which are anchored to the numerous focal adhesion plaques associated with the invasome structure, are typically found to be twisted around its basal part. The formation of invasomes was found to be inhibited by cytochalasin D but virtually unaffected by nocodazole, colchicine or taxol, indicating that invasome-mediated invasion is an actin-dependent and microtubuli-independent process. Bacterial internalisation via the invasome was consistently observed with several clinical isolates of B. henselae, while a spontaneous mutant obtained from one of these isolates was impaired in invasome-mediated invasion. Instead, this mutant showed increased uptake of bacteria into perinuclear localising phagosomes, suggesting that invasome-formation may interfere with this alternative mechanism of bacterial internalisation. Internalisation via the invasome represents a novel paradigm for the invasion of bacteria into host cells which may serve as a cellular colonisation mechanism in vivo, e.g. on proliferating and migrating endothelial cells during Bartonella-induced vaso-proliferative tumour growth.

Topology of Legionella pneumophila DotA: an inner membrane protein required for replication in macrophages

The Legionella pneumophila dotA gene is required for intracellular growth of the bacterium in macrophages. In this study, a structure-function analysis of the DotA protein was conducted to elucidate the role of this protein in L. pneumophila pathogenesis. Translational fusions of dotA to the Escherichia coli phoA and lacZ genes indicated that DotA is an integral cytoplasmic membrane protein with eight membrane-spanning domains. DotA contains two large periplasmic domains of approximately 503 and 73 amino acids and a carboxyl-terminal cytoplasmic domain of 122 amino acids. Protein fractionation studies were consistent with DotA residing in the inner membrane. An alkaline phosphatase fusion located 9 amino acids upstream from the C terminus of DotA still retained function and was able to restore intracellular growth when harbored by two L. pneumophila dotA mutants. A hybrid protein from which the carboxyl-terminal 48 amino acids of DotA were deleted was unable to complement the intracellular growth defect in the dotA mutants, indicating that this cytoplasmic region is required for function.

Intracellular transport of newly synthesized varicella-zoster virus: final envelopment in the trans-Golgi network

The maturation and envelopment of varicella-zoster virus (VZV) was studied in infected human embryonic lung fibroblasts. Transmission electron microscopy confirmed that nucleocapsids acquire an envelope from the inner nuclear membrane as they enter the perinuclear-cisterna-rough endoplasmic reticulum (RER). Tegument is not detectable in these virions; moreover, in contrast to the mature VZV envelope, the envelope of VZV in the RER is not radioautographically labeled in pulse-chase experiments with [3H]mannose, and it lacks gpI immunoreactivity and complex oligosaccharides. This primary envelope fuses with the RER membrane (detected in cells incubated at 20 degrees C), thereby releasing nucleocapsids to the cytosol. Viral glycoproteins, traced by transmission electron microscopy radioautography in pulse-chase experiments with [3H]mannose, are transported to the trans-Golgi network (TGN) by a pathway that runs from the RER through an intermediate compartment and the Golgi stack. At later chase intervals, [3H]mannose labeling becomes associated with enveloped virions in post-Golgi locations (prelysosomes and plasma membrane). Nucleocapsids appear to be enveloped by wrapping in specialized cisternae, identified as the TGN with specific markers. Tegument-like material adheres to the cytosolic face of the concave surface of TGN sacs; nucleocapsids adhere to this protein, which is thus trapped between the nucleocapsid and the TGN-derived membrane that wraps around it. Experiments with brefeldin A suggest that tegument may bind to the cytosolic tails of viral glycoproteins. Fusion and fission convert the TGN-derived wrapping sacs into an inner enveloped virion and an outer transport vesicle that carries newly enveloped virions to cytoplasmic vacuoles. These vacuoles are acidic and were identified as prelysosomes. It is postulated that secreted virions are partially degraded by their exposure to the prelysosomal internal milieu and rendered noninfectious. This process explains the cell-associated nature of VZV in vitro; however, the mechanism by which the virus escapes diversion from the secretory pathway to the lysosomal pathway in vivo remains to be determined.

A new polymorphic methanogen, closely related to Methanocorpusculum parvum, living in stable symbiosis within the anaerobic ciliate Trimyema sp

A new anaerobic microbial consortium has been discovered: the partners are the ciliated protozoon Trimyema sp. and a single species of methanogen. The consortium has been maintained in culture for more than four years. Each ciliate contains up to 300 symbiotic bacteria; many are relatively small and irregularly disc-shaped, and these are distributed throughout the host's cytoplasm, whereas those which are attached to the ciliate's hydrogenosomes are significantly larger and profusely dentate. This attachment is interpreted as an adaptation to maximize capture by the bacteria of the H2 escaping from hydrogenosomes. The 16S rRNA gene of the symbionts has been partially sequenced, and fluorescent oligonucleotide probes have been constructed and used to detect the different morphotypes of the symbiont within the ciliate. The symbionts belong to a new species of archaeobacterium which is a close relative of the free-living methanogen Methanocorpusculum parvum.

Ultrastructural immunocytochemical localization of herpes simplex virus (type 1) in trigeminal ganglion neurons

Four days after corneal inoculation of mice with herpes simplex (type 1) virus (HSV), infected trigeminal ganglion cells with and without calcitonin gene-related peptide (CGRP) antigenicity were examined by electron microscopy in sections treated with colloidal gold labeled antibodies. Cells that contain CGRP were identified by the dense gold labeling of small vesicles about 100 nm in diameter. Adjacent thin sections were stained using an indirect colloidal gold immunocytochemical technique to reveal HSV-1 antigens. In CGRP-positive neurons, HSV antigens were located over both nuclear and cytoplasmic compartments. HSV label was found over cytoplasmic vesicles that were significantly larger than those labeled with anti-CGRP antisera; the HSV-containing vesicles ranged in profile diameter from less than 170 to greater than 400 nm. There was no overlap in the distribution of the two labels. Thus, for this time period, the organelles involved in transport of the endogenous neuropeptide and HSV appear to remain discrete. Furthermore, there was no significant difference in the distribution of HSV in CGRP-reactive and CGRP-negative trigeminal ganglion cells. Thus, there is no indication of a preferential distribution or limited replication of HSV in CGRP-positive neurons.

Ultrastructural behavior of human immunodeficiency virus (HIV) in multinucleated giant cells in the brain of a Japanese hemophiliac presenting AIDS encephalopathy

Human immunodeficiency virus (HIV) was detected ultrastructurally and immunohistochemically in the brain of a Japanese hemophiliac presenting AIDS encephalopathy. The encephalopathy was characterized by the multifocal occurrence of multinucleated giant cells mainly in the subcortical areas. The giant cells were identified immunohistochemically to be macrophages. HIV particles were observed in and out of the giant cells, and most of the particles ingested in the cells were membrane-bound. Some virus particles were found in pinocytic vesicles or phagocytic vacuoles, whereas the others were degradated in the lysosomes of the cells. Budding of HIV particles from the cell surface was also observed, indicating replication of the virus in vivo. These findings suggest ingestion, digestion, and replication of HIV by brain macrophages in AIDS.

Release of simian virus 40 virions from epithelial cells is polarized and occurs without cell lysis

We have investigated the process of release of simian virus 40 (SV40) virions from several monkey kidney cell lines. High levels of virus release were observed prior to any significantly cytopathic effects in all cell lines examined, indicating that SV40 utilizes a mechanism for escape from the host cell which does not involve cell lysis. We demonstrate that SV40 release was polarized in two epithelial cell types (Vero C1008 and primary African green monkey kidney cells) grown on permeable supports; release of virus occurs almost exclusively at apical surfaces. In contrast, equivalent amounts of SV40 virions were recovered from apical and basal culture fluids of nonpolarized CV-1 cells. SV40 virions were observed in large numbers on apical surfaces of epithelial cells and in cytoplasmic smooth membrane vesicles. The sodium ionophore monensin, an inhibitor of vesicular transport, was found to inhibit SV40 release without altering viral protein synthesis or infectious virus production.

Recovery of structurally intact and infectious poliovirus type 1 from HeLa cells during receptor-mediated endocytosis

Poliovirus type 1 enters HeLa cells by receptor-mediated endocytosis as an intact virus. Up to 30 min after adsorption complete virus particles still containing VP4 and sedimenting with 156 S could be recovered from the cells. These virus particles were N-antigenic and infectious. Thirty minutes after adsorption the recovery of intact and infectious virus decreased. This decrease presumably reflects viral uncoating in the acidic endosomes and/or lysosomes because virus particles could be localized in endosomes at this time. The direct involvement of clathrin-coated structures in the endocytosis of poliovirus has been deduced from the enclosure of poliovirus in coated vesicles at 10 min after adsorption. At this time intact and infectious virus could be recovered only after the coated vesicles were disrupted by treatment with 0.5 M Tris at pH 7.0.