Salmonella induced IL-23 and IL-1beta allow for IL-12 production by monocytes and Mphi1 through induction of IFN-gamma in CD56 NK/NK-like T cells

Background

The type-1 cytokine pathway plays a pivotal role in immunity against intracellular bacterial pathogens such as Salmonellae and Mycobacteria. Bacterial stimulation of pattern recognition receptors on monocytes, macrophages and dendritic cells initiates this pathway, and results in the production of cytokines that activate lymphocytes to produce interferon (IFN)-γ. Interleukin (IL)-12 and IL-23 are thought to be the key cytokines required for initiating a type-1 cytokine immune response to Mycobacteria and Salmonellae. The relative contribution of IL-23 and IL-12 to this process is uncertain.

Methodology/Principal Findings

We show that various TLR agonists induce the production of IL-23 but not IL-12 in freshly isolated human monocytes and cultured human macrophages. In addition, type 1 pro-inflammatory macrophages (Mϕ1) differentiated in the presence of GM-CSF and infected with live Salmonella produce IL-23, IL-1β and IL-18, but not IL-12. Supernatants of Salmonella-infected Mϕ1 contained more IL-18 and IL-1β as compared with supernatants of Mϕ1 stimulated with isolated TLR agonists, and induced IFN-γ production in human CD56⁺ cells in an IL-23 and IL-1β-dependent but IL-12-independent manner. In addition, IL-23 together with IL-18 or IL-1β led to the production of GM-CSF in CD56⁺ cells. Both IFN-γ and GM-CSF enhanced IL-23 production by monocytes in response to TLR agonists, as well as induced IL-12 production.

Conclusions/Significance

The findings implicate a positive feedback loop in which IL-23 can enhance its release via induction of IFN-γ and GM-CSF. The IL-23 induced cytokines allow for the subsequent production of IL-12 and amplify the IFN-γ production in the type-1 cytokine pathway.

Intracellular trafficking of Parachlamydia acanthamoebae

Parachlamydia acanthamoebae is an obligate intracellular bacterium that naturally infects free-living amoebae. It is a potential agent of pneumonia that resists destruction by human macrophages. However, the strategy used by this Chlamydia-like organism in order to resist to macrophage destruction is unknown. We analysed the intracellular trafficking of P. acanthamoebae within monocyte-derived macrophages. Infected cells were immunolabelled for the bacteria and for various intracellular compartments by using specific antibodies. We analysed the bacteria colocalization with the different subcellular compartments by using epifluorescence and confocal microscopy. Bacterial replication took place 4-6 h post infection within acidic vacuoles. At that time, P. acanthamoebae colocalized with Lamp-1, a membrane marker of late endosomal and lysosomal compartments. A transient accumulation of EEA1 15 min post infection, and of rab7 and the mannose 6-phosphate receptor 30 min post infection confirmed that P. acanthamoebae traffic through the endocytic pathway. The acquisition of Lamp-1 was not different after infection with living and heat-inactivated bacteria. However, 24.5% and 79.5% of living and heat-inactivated P. acanthamoebae, respectively, colocalized with the vacuolar proton ATPase. Moreover, P. acanthamoebae did not colocalized with cathepsin D, a lysosomal hydrolase, suggesting that P. acanthamoebae interferes with maturation of its vacuole. Thus, P. acanthamoebae survives to destruction by human macrophages probably by controlling the vacuole biogenesis.

Human intestinal microvascular endothelial cells express Toll-like receptor 5: a binding partner for bacterial flagellin

Bacterial flagellin has recently been identified as a ligand for Toll-like receptor 5 (TLR5). Human sites known to specifically express TLR5 include macrophages and gastric and intestinal epithelium. Because infection of intestinal epithelial cells with Salmonella leads to an active transport of flagellin to the subepithelial compartment in proximity to microvessels, we hypothesized that human intestinal endothelial cells functionally express TLR5, thus enabling an active inflammatory response upon binding of translocated flagellin. Endothelial expression of TLR5 in human macro- and microvascular endothelial cells was examined by RT-PCR, immunoblot analysis, and immunofluorescence. Endothelial expression of TLR5 in vivo was verified by immunohistochemistry. Endothelial modulation of ICAM-1 expression was quantitated using flow cytometry, and leukocyte transmigration in vitro was assessed by an endothelial transmigration assay. Epithelial-endothelial cellular interactions upon infection with viable Salmonella were investigated using a coculture system in vitro. We found that Salmonella-infected intestinal epithelial cells induce endothelial ICAM-1 expression in cocultured human endothelial cells. Both macro- (HUVEC) and microvascular endothelial cells derived from human skin (human dermal microvascular endothelial cell 1) and human colon (human intestinal microvascular endothelial cells) were found to express high constitutive amounts of TLR5 mRNA and protein. These findings were paralleled by strong immunoreactivity for TLR5 of normal human colonic microvessels in vivo. Furthermore, incubation of human dermal microvascular endothelial cells with flagellin from clinical isolates of Escherichia and Salmonella strains led to a marked up-regulation of ICAM-1, as well as to an enhanced leukocyte transendothelial cell migration. These results suggest that endothelially expressed TLR5 might play a previously unrecognized role in the innate immune response toward bacterial Ags.

Heterologous expression of a gene encoding a 35 kDa protein of Mycobacterium avium paratuberculosis in Escherichia coli

The full-length open reading frame coding for a potentially immunogenic 35 kDa protein of Mycobacterium avium paratuberculosis was generated using polymerase chain reaction technology. The gene was inserted in-frame into Escherichia coli expression plasmid pQE32. The resulting recombinant plasmid pPMP35 was transformed into E. coli M15. Analysis of the E. coli induced with isopropyl-beta-D-thiogalactopyranoside revealed that the protein accumulated into the cytoplasm as insoluble inclusion bodies. The level of expression of the recombinant 35 kDa protein (P35) was more than 30% of the total protein of E. coli cells. Expression of the recombinant protein was confirmed by immunoblotting. The P35 reacted with a rabbit antiserum raised against a sonicate of M. a. paratuberculosis. The protein was also recognized by serum from a goat with clinical paratuberculosis. Further, a polyclonal antiserum against P35 recognized a 35 kDa band in a membrane fraction of M. a. paratuberculosis. Also, the protein provoked a significant skin reaction in outbred guinea pigs sensitized with M. a. paratuberculosis, as well as in those sensitized with Mycobacterium avium. The results indicate that the 35 kDa protein of M. a. paratuberculosis is a membrane protein, having a role in the cellular immune response.

Antibiotic-induced persistence of cytotoxic Staphylococcus aureus in non-phagocytic cells

OBJECTIVES

After infection of non-phagocytic cells, some Staphylococcus aureus strains are able to survive and kill their host cells. The purpose of this study was to determine the action of various antibiotics on the survival of host cells and/or intracellular S. aureus.

METHODS

Murine keratinocyte (PAM212) and fibroblast (mKSA) cell lines were infected with cytotoxic S. aureus and cultured in the presence of various antibiotics at graded concentrations. The viability of host cells was measured 24 h after infection. To determine the bacterial viability within host cells, cellular lysates were prepared and colony forming units were quantified using a spiral plater. Host cells infected with fluorescein isothiocyanate (FITC)-labelled S. aureus were analysed by flow cytometry and microscopy to determine the subcellular localization S. aureus.

RESULTS

Oxacillin, vancomycin, gentamicin, ciprofloxacin and trimethoprim/sulfamethoxazole did not rescue host cells from cell death induced by intracellular S. aureus. In contrast, linezolid, rifampicin, azithromycin, clindamycin, erythromycin and quinupristin/dalfopristin suppressed the cytotoxic action of S. aureus. After withdrawal of antibiotics, intracellular S. aureus regained cytotoxic activity and killed their host cells. Only rifampicin was able to eliminate intracellular S. aureus completely within 72 h. In contrast, clindamycin, azithromycin and linezolid induced a state of intracellular persistence of viable S. aureus.

CONCLUSIONS

Antibiotics commonly used for the management of S. aureus infections appear to create a niche for invasive intracellular S. aureus, which may play an important role for persistence and recurrence of infection. Because of its unique ability to eliminate intracellular S. aureus, rifampicin appears to be valuable for the treatment of invasive S. aureus infections.

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.

Host defense role of platelets: engulfment of HIV and Staphylococcus aureus occurs in a specific subcellular compartment and is enhanced by platelet activation

Platelets can bind and phagocytose infectious microorganisms and so enable their transport for a prolonged time. To investigate the subcellular events of these interactions, platelets were incubated either with Staphylococcus aureus or with HIV and analyzed by electron microscopy (EM) and immuno-EM. HIV and bacteria internalization occurred exclusively within platelets showing morphological evidence of activation. Platelet activation enhanced the degree of bacterial internalization. Immunolabeling revealed that the engulfing vacuoles and the open canalicular system (OCS) were composed of distinct antigens. The engulfing vacuoles eventually became the site of prominent alpha-granule release. In platelets incubated with HIV, characteristic endocytic vacuoles were identified close to the plasma membrane, tightly surrounding 1 or 2 HIV particles. Virus particles were also located within the OCS. Immunogold labeling for the viral core protein p24 confirmed the presence of HIV within platelets. Finally, examination of platelets from a patient with acquired immunodeficiency syndrome and high viremia suggested that HIV endocytosis may also occur in vivo.

Temporal and subcellular localization of PR-1 proteins in tomato stem tissues infected by virulent and avirulent isolates of Phytophthora capsici

Immunoblot analysis and immunogold labeling of PR-1 protein (pathogenesis-related protein 1) in tomato (Lycopersicon esculentum Mill.) were performed to examine the temporal and spatial expression patterns of PR-1 protein induced by Phytophthora capsici infection. Soluble proteins with molecular masses of 10, 17, 25, 27 and 75 kDa were induced and accumulated in P. capsici-infected stem tissues during the compatible and incompatible interactions. Western blot analysis revealed that expression of PR-1 protein (17 kDa), at 12 to 24 h after inoculation, occurred earlier in the incompatible than in the compatible interaction. Immunogold labeling of PR-1 proteins occurred over cell walls and cytoplasm of the host and the oomycete pathogen and at the interface between host and oomycete cell walls at 24 h after inoculation in the compatible interaction. In the incompatible interaction, numerous PR-1 proteins accumulated predominantly over oomycete cell walls and at the interface between host and oomycete cell walls. The quantity of PR-1 proteins deposited in both host and oomycete cells was much less in the compatible than the incompatible interaction. Healthy tomato stem tissue was nearly free of immunogold labeling of PR-1 proteins.

Identification of distinct lymphocyte subsets responding to subcellular fractions of Mycobacterium bovis bacille calmette-Guérin (BCG)

In order to investigate the ability of Mycobacterium bovis BCG vaccination to induce immune responses toward different classes of mycobacterial antigens and the cell populations involved in such responses, proliferation of distinct human lymphocyte subsets from BCG-vaccinated donors in response to different subcellular fractions of BCG was analysed and compared with that of not sensitized subjects. Proliferation of different cell subsets was evaluated by flow cytometric determination of bromodeoxyuridine incorporated into DNA of dividing cells and simultaneous identification of cell surface markers. Although a certain degree of variability was observed among different donors, after 6 days of in vitro stimulation BCG-vaccinated subjects displayed, as a mean, a stronger blastogenic response to all the classes of antigens compared with non-sensitized ones. PPD, culture filtrates and membrane antigens induced a predominant proliferation of CD4+ T cells. In contrast, preparations enriched in cytosolic antigens elicited strong proliferation of gammadelta+ T cells which, as a mean, represented 55% of the proliferating cells. Although to a lesser extent, proliferation of gammadelta+ T cells was also elicited by preparations enriched in membrane and cell wall antigens. In response to the latter preparation proliferation of CD4+ T cells and CD16+/CD3- (natural killer (NK)) cells was observed, as well. In particular, cell wall antigens were found to induce significantly higher levels of proliferation of NK cells compared with all the other classes of antigens.

Mycobacterium tuberculosis inhibits IFN-gamma transcriptional responses without inhibiting activation of STAT1

IFN-gamma activates macrophages to kill diverse intracellular pathogens, but does not activate human macrophages to kill virulent Mycobacterium tuberculosis. We tested the hypothesis that this is due to inhibition of IFN-gamma signaling by M. tuberculosis and found that M. tuberculosis infection of human macrophages blocks several responses to IFN-gamma, including killing of Toxoplasma gondii and induction of FcgammaRI. The inhibitory effect of M. tuberculosis is directed at transcription of IFN-gamma-responsive genes, but does not affect proximal steps in the Janus kinase-STAT pathway, as STAT1alpha tyrosine and serine phosphorylation, dimerization, nuclear translocation, and DNA binding are intact in M. tuberculosis-infected cells. In contrast, there is a marked decrease in IFN-gamma-induced association of STAT1 with the transcriptional coactivators CREB binding protein and p300 in M. tuberculosis-infected macrophages, indicating that M. tuberculosis directly or indirectly disrupts this protein-protein interaction that is essential for transcriptional responses to IFN-gamma. Gamma-irradiated M. tuberculosis and isolated cell walls reproduce the effects of live bacteria, indicating that the bacterial component(s) that initiates inhibition of IFN-gamma responses is constitutively expressed. Although lipoarabinomannan has been found to exert effects on macrophages, it does not account for the inhibitory effects of cell walls. These results indicate that one mechanism for M. tuberculosis to evade the human immune response is to inhibit the IFN-gamma signaling pathway, and that the mechanism of inhibition is distinct from that reported for Leishmania donovani or CMV, in that it targets the interaction of STAT1 with the basal transcriptional apparatus.

The EspB protein of enteropathogenic Escherichia coli is targeted to the cytoplasm of infected HeLa cells

The EspB protein of enteropathogenic Escherichia coli (EPEC) is exported via a type III secretion apparatus. EspB is critical for signaling the host cell and for the development of the attaching and effacing lesion characteristic of EPEC infection. We used cellular fractionation and confocal laser scanning microscopy to determine the cellular location of EspB during infection of HeLa cells. Both methods indicated that EspB is targeted to the cytoplasm of infected cells. Using mutants, we found that EspB targeting to the host cell cytoplasm requires the type III secretion apparatus and the secreted proteins EspA and EspD, but not intimin. These results provide insights into the function of the type III secretion apparatus of EPEC and the functions of the Esp proteins.

Subcellular fractionation by organelle electrophoresis: separation of phagosomes containing heat-killed yeast particles

Uptake of foreign material and its subsequent lysosomal degradation is an important function of macrophages. The mechanisms involved in the binding, uptake and delivery of such material to lysosomal organelles, are, however, poorly understood. Here we describe a method using organelle electrophoresis to study the uptake and trafficking of heat-killed yeast particles within murine macrophages. Such yeast particles, which were fluorescently labeled, could be readily detected in intact cells as well as in subcellular fractions. Organelle electrophoresis of a homogenate from macrophages that had internalized yeast particles resulted in the separation of yeast-containing organelles from most other subcellular membranes. In addition, this method was used to follow the kinetics of yeast particle transport within macrophages could be followed readily. Organelle electrophoresis may be a valuable tool for the analysis of phagocytosis.

Defective export in Escherichia coli caused by DsbA'-PhoA hybrid proteins whose DsbA' domain cannot fold into a conformation resistant to periplasmic proteases

The disulfide bond-forming factor DsbA and the alkaline phosphatase are stable in the Escherichia coli periplasmic space and can be overproduced without significant perturbation of the cell's physiology. By contrast, DsbA'-PhoA hybrid proteins resulting from TnphoA insertions into different regions of a plasmid-borne dsbA gene could become toxic (lethal) to bacteria. Toxicity was concomitant with an impairment of some step of the export mechanism and depended on at least three parameters, i.e., (i) the rate of expression of the hybrid protein, (ii) the ability of the amino-terminal DsbA' domain of the hybrid protein to fold into a protease-resistant conformation in the periplasmic space, and (iii) the activity of the DegP periplasmic protease. Even under viable conditions of low expression, DsbA' folding-deficient hybrid proteins accumulated more than the folding-proficient ones in the insoluble material and this was aggravated in a strain lacking the DegP protease. When production was more elevated, the folding-deficient hybrid proteins became lethal, but only in strains lacking the DegP activity, while the folding-proficient ones were not. Under conditions of very high production by degP+ or degP strains, both types of hybrid proteins accumulated as insoluble preproteins. Meanwhile, the export machinery was dramatically handicapped and the cells lost viability. However, the folding-deficient hybrid proteins had a higher killing efficiency than the folding-proficient ones. Free DsbA'-truncated polypeptides, although not toxic, were processed more slowly when they could not fold into a protease-resistant form in the periplasmic space. This provides indications in E. coli for a direct or indirect influence of the folding of a protein in the periplasmic environment on export efficiency.

Subcellular localization of the 65-kDa heat shock protein in mycobacteria by immunoblotting and immunogold ultracytochemistry

The 65-kDa heat shock protein (hsp65) is an immunodominant antigen in mycobacterial infections and also the key etiologic factor in mycobacteria-induced autoimmune arthritis. Because the subcellular distribution of hsp65 in the mycobacteria may be relevant to understand its immunoreactivity, we have investigated the presence of hsp65 in the envelope and cytoplasmic compartments of the bacilli. Anti-hsp65 antibodies were used in western blottings to investigate the presence of hsp65 in cell fractions (membrane, envelope and cytosol) of Mycobacterium avium and M. smegmatis, and also to label hsp65 in situ by the immunogold method on thin-sectioned mycobacteria, including the non-cultivable M. leprae, that were studied by transmission electron microscopy. All of the three subcellular mycobacterial fractions showed significant labelling by anti-hsp65 antibodies. Immunogold ultracytochemistry revealed the presence of hsp65 in both the cytoplasm and the envelope of mycobacteria. The data indicate that hsp65 molecules are commonly present not only in the cytoplasm but also in the envelope of mycobacteria. The latter topography of hsp65 may contribute to the strong immunogenicity of hsp65 since it may correspond to export hsp65 molecules captured before being secreted into the extracellular milieu, thus making hsp65 a mycobacterial antigen readily available for presentation to the immune system of infected hosts.

Biosynthesis and biochemical properties of the hepatitis C virus core protein

The biosynthesis and biochemical properties of the putative nucleocapsid protein of hepatitis C virus (HCV) were investigated. RNA transcripts for cell-free translation were prepared from truncated form of the cDNA construct encoding the structural proteins of HCV. Processing of the translation products was dependent on microsomal membranes and signal recognition particle, suggesting that release of the 21-kDa core protein from the polyprotein precursor is mediated solely by the signal peptidase of the endoplasmic reticulum (ER) and is achieved by the removal of a putative signal sequence of approximately 18 residues located at its C terminus. The core protein was found to bind membranes in vitro and in transfected cells, as shown by centrifugation analysis of in vitro translation products and transfected-cell lysates. Immunofluorescence of transfected cells showed that the core protein colocalized with the E2 glycoprotein as well as with a cellular ER membrane marker. The nucleocapsid protein expressed by in vitro translation in rabbit reticulocyte lysates cosedimented with the large ribosomal subunit in sucrose gradients. The ribosome binding domain was mapped to the N-terminal region of the core protein. Moreover, the same region was shown to bind RNA in vitro, suggesting that cosedimentation of core protein with ribosomes may be mediated by the RNA binding of the nucleocapsid protein of HCV. These studies indicate that the HCV core protein is a cytoplasmic protein associated with the ER membranes and possesses RNA binding activity.

Rous sarcoma virus RNA stability requires an open reading frame in the gag gene and sequences downstream of the gag-pol junction

The intracellular accumulation of the unspliced RNA of Rous sarcoma virus was decreased when translation was prematurely terminated by the introduction of nonsense codons within its 5' proximal gene, the gag gene. Subcellular fractionation of transfected cells suggested that nonsense codon-mediated instability occurred in the cytoplasm. Analysis of constructs containing an in-frame deletion in the nucleocapsid domain of gag, which prevents interaction between the Gag protein and viral RNA, showed that an open reading frame extending to approximately 30 nucleotides from the natural gag termination codon was needed for RNA stability. Sequences at the gag-pol junction necessary for ribosomal frameshifting were not required for RNA stability; however, sequences located 100 to 200 nucleotides downstream of the natural gag termination codon were found to be necessary for stable RNA. The stability of RNAs lacking this downstream sequence was not markedly affected by premature termination codons. We propose that this downstream RNA sequence may interact with ribosomes translating gag to stabilize the RNA.

Characterization of an azole-resistant Candida glabrata isolate

A Candida (Torulopsis) glabrata strain (B57149) became resistant to fluconazole after a patient carrying the organism was treated with the drug at 400 mg once daily for 9 days. Growth of the pretreatment isolate (B57148) was inhibited by 50% with 0.67 microM ketoconazole, 1.0 microM itraconazole, and 43 microM fluconazole, whereas growth of B57149 was inhibited slightly by 10 microM ketoconazole but was unaffected by 10 microM itraconazole or 100 microM fluconazole. This indicates cross-resistance to all three azole antifungal agents. The cellular fluconazole content of B57149 was from 1.5- to 3-fold lower than that of B57148, suggesting a difference in drug uptake between the strains. However, this difference was smaller than the measured difference in susceptibility and, therefore, cannot fully explain the fluconazole resistance of B57149. Moreover, the intracellular contents of ketoconazole and itraconazole differed by less than twofold between the strains, so that uptake differences did not account for the azole cross-resistance of B57149. The microsomal cytochrome P-450 content of B57149 was about twice that of B57148, a difference quantitatively similar to the increased subcellular ergosterol synthesis from mevalonate or lanosterol. These results indicate that the level of P-450-dependent 14 alpha-demethylation of lanosterol is higher in B57149. Increased ergosterol synthesis was also seen in intact B57149 cells, and this coincided with a decreased susceptibility of B57149 toward all three azoles and amphotericin B. B57149 also had higher squalene epoxidase activity, and thus, more terbinafine was needed to inhibit the synthesis of 2,3-oxidosqualene from squalene. P-450 content and ergosterol synthesis both decreased when isolate B57149 was subcultured repeatedly on drug-free medium. This repeated subculture also fully restored the strain's itraconazole susceptibility, but only partly increased its susceptibility to fluconazole. The results suggest that both lower fluconazole uptake and increased P-450-dependent ergosterol synthesis are involved in the mechanism of fluconazole resistance but that only the increased ergosterol synthesis contributes to itraconazole cross-resistance.

Metabolism of hexadecyltrimethylammonium chloride in Pseudomonas strain B1

A bacterium (strain B1) utilizing hexadecyltrimethylammonium chloride as a carbon and energy source was isolated from activated sludge and tentatively identified as a Pseudomonas sp. This bacterium only grew on alkyltrimethylammonium salts (C12 to C22) and possible intermediates of hexadecyltrimethylammonium chloride breakdown such as hexadecanoate and acetate. Pseudomonas strain B1 did not grow on amines. Simultaneous adaptation studies suggested that the bacterium oxidized only the alkyl chain of hexadecyltrimethylammonium chloride. This was confirmed by the stoichiometric formation of trimethylamine from hexadecyltrimethylammonium chloride. The initial hexadecyltrimethylammonium chloride oxygenase activity, measured by its ability to form trimethylamine, was NAD(P)H and O2 dependent. Finally, assays of aldehyde dehydrogenase, hexadecanoyl-coenzyme A dehydrogenase, and isocitrate lyase in cell extracts revealed the potential of Pseudomonas strain B1 to metabolize the alkyl chain via beta-oxidation.

Posttranslational modification and subcellular localization of the p12 capsid protein of herpes simplex virus type 1

We have previously shown that the 12-kDa capsid protein (p12) of herpes simplex virus type 1 (HSV-1) is a gamma 2 (true late) gene product encoded by the UL35 open reading frame (D. S. McNabb and R. J. Courtney, J. Virol. 66:2653-2663, 1992). To extend the characterization of p12, we have investigated the posttranslational modifications and intracellular localization of the 12-kDa polypeptide. These studies have demonstrated that p12 is modified by phosphorylation at serine and threonine residues. In addition, analysis of p12 by acid-urea gel electrophoresis has indicated that the protein can be resolved into three components, designated p12a, p12b, and p12c. Using isotopic-labeling and alkaline phosphatase digestion experiments, we have determined that p12a and p12b are phosphorylated forms of the protein, and p12c is likely to represent the unphosphorylated polypeptide. The kinetics of phosphorylation was examined by pulse-chase radiolabeling, and these studies indicated that p12c can be completely converted into p12a and p12b following a 4-h chase. All three species of p12 were found to be associated with purified HSV-1 virions; however, p12b and p12c represented the most abundant forms of the protein within viral particles. We have also examined the intracellular localization of p12 by cell fractionation and indirect immunofluorescence techniques. These results indicated that p12 is predominantly localized in the nucleus of HSV-1-infected cells and appears to be restricted to specific regions within the nucleus.

Viral RNA synthesis in tomato spotted wilt virus-infected Nicotiana rustica plants

The synthesis of viral RNA species in tomato spotted wilt virus-infected Nicotiana rustica plants was followed in terms of time and relative abundance. Systemic symptoms were visible after 4 days postinoculation (p.i.), but viral (v) and viral-complementary (vc) strands of all three genomic RNA segments [large (L) RNA, medium (M) RNA and small (S) RNA] were detected from 2 days p.i. In addition, two subgenomic mRNAs, derived from S RNA, were detected. For the L RNA segment no subgenomic mRNAs were detected, suggesting that this segment is expressed via the synthesis of a genome-sized vc mRNA. A possible M-specific subgenomic mRNA was detected, showing a similar time course of appearance as the subgenomic mRNAs derived from the S RNA segment. Analysis of cytoplasmic RNA fractions revealed that both v and vc strands of all three genomic segments associate with the nucleocapsid protein into nucleocapsid structures, the vcRNA species being present in lower amounts. Intact, enveloped virus particles contained only the v strand of the L RNA segment and, surprisingly, both v and vc strands of the M and S RNA segment, though in different ratios.

Subcellular distribution and life cycle of Epstein-Barr virus in keratinocytes of oral hairy leukoplakia

The authors investigated the life cycle of Epstein-Barr virus (EBV) in keratinocytes of oral hairy leukoplakia by combining immunohistochemistry. DNA in situ hybridization, and lectin histochemistry with electron microscopy. Diffuse-staining components of the EBV early antigen complex (EA-D), EBV 150-kd capsid antigen (VCA), EBV membrane antigen (gp350/220), and double-stranded DNA were labeled with monoclonal antibodies. An EBV-DNA probe was used to locate EBV DNA. Wheat-germ agglutinin (WGA) was employed to distinguish Golgi-associated compartments. The authors found EBV proteins and EBV DNA only in keratinocytes with apparent viral assembly. In situ hybridization showed EBV DNA in free corelike material and in electron-dense cores of mature nucleocapsids. Monoclonal antibodies to nonspecific double-stranded DNA attached to the same structures and to marginated chromatin. Components of EA-D were dispersed throughout the nuclei but accumulated near condensed chromatin and in 'punched-out' regions of the chromatin. Epstein-Barr virus 150-kd capsid antigen was found only in the nuclei, where it appeared preferentially on mature nucleocapsids. As yet unexplained arrays of intranuclear particles that remained unlabeled with all EBV-specific probes reacted intensely with an antiserum against common papillomavirus antigen. Gp350/220 was detectable in various cellular membrane compartments and was highly concentrated on EBV envelopes in peripheral Golgi-associated secretory vesicles. It was less abundant on the extracellular EBV, indicating that viral membrane antigen partly dissociates from the mature virus. Combined lectin-binding histochemistry and electron microscopy demonstrated for the first time that EBV is processed in the Golgi apparatus, which eventually releases the virus by fusion with the plasma membrane. These results provide insight into the biologic events that occur during complete EBV replication in vivo.

Subcellular distribution of the major immediate early proteins of human cytomegalovirus changes during infection

The 72K immediate early (IE) 1 protein of human cytomegalovirus and the 68K protein, also encoded by the IE1 gene, were detected by immunoelectron microscopy using monoclonal antibodies specific for the 68K or 72K proteins. Early after infection, both proteins were localized to the nucleus, but with different localization patterns. Late after infection, both of the proteins decreased markedly in the nucleus, in which nucleocapsids appeared. Simultaneously, the 68K protein became diffusely distributed in the cytoplasm and the plasma membrane, whereas the 72K protein was distributed in the nuclear envelope and the plasma membrane. Both proteins were also observed in the coating membrane of the extracellular dense bodies.

Expression of the 16K cistron of tobacco rattle virus in protoplasts

An antiserum was raised against a synthetic peptide corresponding to the 18 C-terminal amino acids of a putative 16K protein encoded by the 3'-terminal open reading frame of tobacco rattle virus (TRV) RNA-1. This antiserum was used to demonstrate expression of the 16K cistron in vivo. TRV-infected tobacco protoplasts accumulated similar amounts of 16K protein and viral coat protein but in tobacco plants only the coat protein was detectable. Time course experiments revealed that in protoplasts the accumulation of 16K protein lagged somewhat behind that of coat protein. The 16K protein was incorporated in a high-molecular-weight cellular component that was resistant to treatment with nonionic detergents.

Subcellular distribution of the transmissible agent in Creutzfeldt-Jakob disease mouse brain

To determine the intracellular localization of the Creutzfeldt-Jakob disease (CJD) agent in mouse brain, cerebrum tissue of the mouse brain affected with the Fukuoka-1 strain was separated into six subcellular fractions (microsome, nerve ending, myelin, mitochondria, nucleus, and soluble fractions) by differential sucrose density gradient, and then the CJD infectivity of these fractions was examined. Serially diluted samples of each subfraction were inoculated intracerebrally into groups of BALB/c mice, and the infectivity was determined as to end point titration value, incubation period, and number of affected mice. On the basis of the protein content, the highest CJD infectivity was observed in the microsomal fraction. The nerve ending (synaptic plasma membrane) and myelin fractions were also infective. The mitochondria and nucleus fractions showed the lower infectivity. The infectivity of the soluble fraction was the lowest among the six subcellular fractions. From the findings obtained in this study two possibilities as to the intracellular localization of CJD agent were suggested: 1) the transmissible agent of CJD is closely associated with surface membranes of neuronal and/or glial cells, including their processes; 2) the CJD agent is diffusely present intracellularly, including in the surface membranes, but for manifestation of infectivity the agent needs membrane components as prerequisite factors.

Productive infection by B19 parvovirus of human erythroid bone marrow cells in vitro

B19 parvovirus, the cause of fifth disease and transient aplastic crisis, has been successfully propagated in suspension cultures of human erythroid bone marrow cells obtained from patients with sickle cell disease and stimulated by erythropoietin. B19 inoculation in vitro resulted in a marked decline in identifiable erythroid cells over seven to nine days of incubation. Characteristic giant early erythroid cells were seen on Wright's-Giemsa stain of infected cultures. By in situ hybridization, 30% to 40% of erythroblasts were infected at 48 hours; a similar proportion of cells showed B19 capsid protein by immunofluorescence. B19 DNA was present in erythroblasts but not in the leukocyte fraction of bone marrow. B19 replication, as determined by Southern analysis, and B19 encapsidation, as determined by sensitivity of isolated cell fractions to DNase I, were restricted to the nuclei. B19 DNA was detectable in the nuclei from infected cultures beginning at 18 hours and in the supernatant at 32 hours; B19 genome copy number was estimated at about 25,000 to 30,000/infected cell at 48 hours. Recovery of virus depended on the multiplicity of infection (moi); at low moi, approximately 200x input virus was recovered from total cultures and 50x from the culture supernatants. Virus released into the supernatant was as infectious or more infectious than virus obtained from sera of infected patients. Human erythroid bone marrow culture represents a safe in vitro system for the elucidation of the cellular and molecular biology of the pathogenic B19 parvovirus.

Suppression of endocytosis in neutrophils by influenza A virus in vitro

The effect of influenza A virus on the endocytic pathway in polymorphonuclear leukocytes (PMNLs) and the relationship of altered endocytic activity to virus-induced inhibition of other PMNL functions were examined with virus that caused decreased phagosomelysosome fusion and bacterial killing (depressing virus [DV]) and virus that did not (non-DV). Binding of both viruses to PMNL surface receptors was similar, but uptake of DV into PMNLs was decreased compared with that of non-DV. Both viruses were associated with the PMNL plasma membrane and were in endosomes. DV caused less stimulation of pinocytosis than did non-DV. The rate of exocytosis of fluoresceinated-dextran (FL-dextran) from cells stimulated with DV was significantly less than for non-DV. When PMNLs were pretreated with buffer, DV, or non-DV and then exposed to FL-dextran and N-formylmethionylleucylphenylalanine, the pinocytosis of FL-dextran was significantly less in cells pretreated with DV as compared with non-DV or buffer.

Kilham rat virus DNA replication in subcellular fractions

A subcellular system actively replicating Kilham rat virus DNA in vitro was developed. Cellular lysates and isolated nuclei from infected cells showed an amplification of replicative forms in vitro. Solubilized replicative complexes, either partly purified or in the form of a crude extract, were able to synthesize replicative forms and single-stranded DNA. DNA polymerase alpha played a major role in Kilham rat virus DNA synthesis in vivo and in vitro. Furthermore, a factor present in the cytosol of infected cells increased the polymerizing activity of viral replicative complexes.

Mode of penetration and intracellular localization of incoming parental foot and mouth disease virus (FMDV) in BHK cells

The process of penetration and subsequent early stages of replication of Foot and Mouth Disease Virus (FMDV) in BHK21 cell cultures have been studied in order to obtain further data about the infectious cycle of this virus. Results suggest that FMDV penetrates BHK21 cells by way of pinocytic vesicles. Studies of lysosomal (LF) and supernatant (SF) fractions of homogenized suspension of infected cells were carried out to learn the percentage of possible non-specific absorption of infectious virus particles. Furthermore, analysis of intracellular virus shows that LF-associated virus is not completely degraded by the enzymatic process expressed by cellular proteases and RNAses and can be potentially useful for genetic expression. Data suggest that: i) only a part of LF-associated virus replicates; ii) the remaining LF-associated virus may be a reservoir of potentially active virus.

Cellular antibiotic pharmacology

Many perinatal pathogens are able to survive and in some cases replicate intracellularly. With the exception of viruses and toxoplasma, these pathogens principally infect phagocytic cells of the reticuloendothelial system. Such intracellular organisms, by evading the effects of antibiotics that act only extracellularly, may respond poorly to conventional therapy. Of currently available antibiotics, rifampin, chloramphenicol and trimethoprim are the most active intracellularly. Other antibiotics are either taken up by cells but appear to be inactive intracellularly (lincomycin) or are excluded from cells (penicillins, cephalosporins, aminoglycosides). The clinical role of antibiotics that are active intracellularly is not clear; anecdotal human experience and limited controlled animal experience suggests that they may be useful in the treatment of some infections. Because of the decreased microbicidal activity of newborn phagocytes, intracellular activity of antibiotics may be of greater importance than in older patients. Further study is needed to answer these questions. Methods of enhancing intracellular activity of antibiotics are available should this property prove to be desirable.

[Abortive influenza virus infection of Ehrlich cells. Virion and subcellular fraction proteins]

Ehrlich ascitic carcinoma cells infected with the WSN strain of influenza virus produced noninfectious virus particles containing no M protein. Polypeptides P1, NP, and NS were synthesized in the infected ascites cells to the same concentration was in permissive cells (chick fibroblasts and MDCK cells); the synthesis of HA and M proteins was markedly disturbed, however. In the permissive cells, M protein was found in the fraction of the perinuclear martial and plasma membranes whereas in the ascitic cells M protein was detected only in perinuclear material but not in plasma membrane. Thus, nonpermissiveness of the ascitic cells appears to be due to disturbance of both synthesis and transport of M protein to the plasma membrane.

Role of endogenous murine leukemia virus in immunologically triggered lymphoreticular tumors. I. Development and use of oncogenic cellfree preparations serially passaged in vivo

Cellfree extracts (CFEs) prepared from (BALB/cJ X A/J)F1 (CAF1) and (BALB/cJ X C57BL/6J)F1 (CB6F1) mice in which a graft-versus-host reaction (GVHR) has been induced are known to be oncogenic, but only after a protracted latent period (mean, 16 mo). Serial passage of such CFEs in successive generations of syngeneic mice inoculated at birth led to the development of two separate oncogenic preparations, the CA serioes in CAF, mice and the CB series in CB6F, mice, in which the mean latent period was reduced to 6 and 12 months, respectively. Both oncogenic preparations contained infectious B-tropic murine leukemia virus (MuLV) and particles with the ultrastructural characteristics of MuLV. No other kind of virus particle was seen. When these preparations were injected into infant syngeneic mice, B-tropic MuLV could be detected in the reticular tissues as early as 2 weeks thereafter. The virus persisted in the reticular tissues and was present in the lymphoreticular tumors that subsequently developed. However, if the same preparation was injected into young adult recipients, there may have been transient MuLV replication, but the virus subsequently disappeared from the reticular tissues and no lymphoreticular tumors developed. Previous experiments showed that MuLV was present in CFEs prepared from CAF, animals with the GVHR but absent in those of normal control mice. Since the lymphoreticular tumors arising in mice with the GVHR were the same as those induced by the CA and CB MuLV preparations, it was concluded that tumorigenesis in mice with the GVHR was caused by endogenous B-tropic MuLV activated by the immunologic disturbance.

Infection at the subcellular level. I. Localization of intravenously injected brucellae in the vacuolar apparatus of cells of guinea pig liver

The distribution of Brucella melitensis in various tissues and in subcellular fractions obtained from liver was investigated to evaluate the initial phases of brucellosis in the guinea pig. Fifty minutes after intravenous infection, brucellae were found principally in the blood and liver, with a substantial number recovered from spleen. Fractionation of liver established that most bacteria were found in the mitochondrial plus lysosomal (M + L) fraction; a significant number, however, sedimented in the nuclear (N) fraction. With time, there was a progressive shift of bacteria from the M + L to the N fraction, accompanied by a similar shift in acid phosphatase activities. Isopycnic centrifugation of mixtures of M + L fractions and brucellae permitted complete separation of acid phosphatase-bearing particles from bacteria. Similar experiments with fractions from infected animals showed that viable bacteria were found in both the acid phosphatase and free brucellae regions of the gradient. At 10 min postinfection, 52% of the recovered organisms were in the acid phosphatase region; at 30 min, 65%; at 60 min, 85%; and at 315 min, 79%. Detergent plus sonic treatment of an M + L fraction from the liver of an animal killed 50 min after infection caused most of the bacteria in the acid phosphatase region to shift to the region where free bacteria were found. These data suggested that brucellae sequestered in the liver were located primarily in the vacuolar apparatus of the cells which phagocytized them.