Identification of phagocytosed Pneumocystis carinii in human pulmonary alveolar macrophages

Examination of Papanicolaou-stained bronchoalveolar lavage samples from cases with Pneumocystis carinii pneumonitis under ultra-violet light reveals alveolar macrophages packed with fluorescent inclusions. Immunoenzymatic staining of the alveolar macrophages with a monoclonal antibody specific for P. carinii (3F6) showed that these inclusions contain intact pneumocysts or their degradation products. Fluorescence microscopy of Papanicolaou-stained smears is advocated as a sensitive and specific method of diagnosing P. carinii infection.

Subgenomic RNAs of Lelystad virus contain a conserved leader-body junction sequence

During the replication of Lelystad virus in alveolar lung macrophages, a 3'-coterminal nested set of six subgenomic RNAs (RNA2 to RNA7) is formed. These contain a common leader sequence derived from the 5' non-coding region of the genomic RNA. In this study, the sequence of the junction sites, i.e. the sites where the leader sequence joins to the body of the subgenomic RNA, was determined for all six subgenomic RNAs. For each subgenomic RNA, six to nine cDNA clones were isolated by means of reverse transcription and PCR. The nucleotide sequence at the junction site was identical for all eight cDNA clones derived from subgenomic RNA4. However, heterogeneity was observed in the nucleotide sequence surrounding the junction sites of the cDNA clones derived from subgenomic RNAs 2, 3, 5, 6 and 7. This heterogeneity suggests that the fusion of the leader to the body of the subgenomic RNA may be imprecise. The junction sites of the six subgenomic RNAs had a conserved sequence motif of six nucleotides (UCAACC or a highly similar sequence). The distance between the junction site and the translation initiation codon of the downstream open reading frame varied from nine to 83 nucleotides.

Influence of methylprednisolone on the intracellular antimicrobial activity of erythromycin and clindamycin against Legionella pneumophila

We have investigated the effect of methylprednisolone on the intracellular activity of erythromycin and clindamycin in vitro. An assay system was developed for the determination of intracellular activity of antibiotics against Legionella pneumophila using guinea pig resident alveolar macrophages. Erythromycin at a concentration of 0.625 mg/L (5 x MIC) and clindamycin at a concentration of 8 mg/L (MIC) inhibited the growth of a single strain of L. pneumophila in macrophages, whilst ceftizoxime at a concentration of 0.625 mg/L (5 x MIC) did not. Methylprednisolone at therapeutic concentrations did not affect the intracellular antibacterial activity of either erythromycin or clindamycin against L. pneumophila. We found no direct effect of methylprednisolone on the intracellular antibacterial activity of either erythromycin or clindamycin.

Uniform detection of HIV-1 in alveolar macrophages of pediatric but not adult AIDS patients

Manifestations of pulmonary disease in pediatric AIDS patients differ from those in adults. To evaluate whether differences in the frequency of alveolar macrophage (AM) infection with human immunodeficiency virus type 1 (HIV-1) could account for these clinical distinctions, we undertook a comparative analysis of HIV-1 DNA in AMs from pediatric and adult AIDS patients by enzymatic amplification. A higher frequency of viral DNA detection in pediatric cases (100%) compared with adults (67%) was observed. The sensitivity of detection was 1 viral DNA copy per 4000 AMs; matched peripheral blood mononuclear cells from six of seven pediatric and eight of nine adult patients tested HIV-1 DNA positive. Adult but not pediatric patients exhibited a marked alveolar lymphocytosis, 32% mean lymphocyte count compared with 7.0%, respectively. These results suggest that the burden of HIV-1 in the lungs of pediatric AIDS patients is greater than that in adults.

[Experimental reproduction of the respiratory form of infection with the agent of epidemic late abortion of swine]

Porcine reproductive and respiratory syndrome has been observed in a large swine-farm. Diagnostic investigations were undertaken. Piglets infected with homogenate from the lung of a sick gilt developed biphasic fever up to 42 degrees C, inappetence and apathy. A few piglets showed red-blue discolored parts of the ears and of the skin in the abdominal region. A cytopathogenic agent has been isolated on cultivated alveolar-macrophages. Infection of another group of piglets with macrophages-propagated agent resulted in similar clinical signs too. Organs of euthanatized piglets have been examined anatomical, histological and with the fluorescent antibody technique. Specific fluorescence could be seen in tonsils, bronchial lymph nodes, spleen and in pathological-changed parts of the lungs. Antibodies against PRRS-virus were detected in blood samples of experimentally infected pigs.

Resistance to nitric oxide in Mycobacterium avium complex and its implication in pathogenesis

Susceptibility of three different strains of Mycobacterium avium complex (MAC), i.e., one strain of M. avium (Mino) and two strains of M. intracellulare (31F093T and KUMS 9007), to nitric oxide (NO) generated by rat alveolar macrophages (M phi) or NO generated chemically by acidification of NO2- was examined in vitro. We also investigated the effects of NO on phagocytosis and superoxide anion (O2-) generation by M phi. The intracellular growth of M. avium Mino was significantly suppressed by NO generated by gamma interferon (IFN-gamma)-stimulated M phi, whereas that of two strains of M. intracellulare (31F093T and KUMS 9007) was not. M. avium Mino was also more susceptible to NO generated chemically by acidification of NO2- than the two M. intracellulare strains. In L-arginine (1 mM)-containing medium, NO release from the M phi assessed by measuring NO2- increased as the concentration of IFN-gamma increased. The enhancing potential of IFN-gamma for NO release became more pronounced when M phi were infected with 31F093T, an NO-resistant strain. A large amount of NO generated by IFN-gamma-stimulated M phi suppressed both phagocytosis and O2- generation by the M phi, especially after infection of the M phi with strain 31F093T. These results indicate that the intracellular growth of MAC is not always inhibited by NO generated by immunologically activated M phi; rather, NO generation induced by infection with an NO-resistant MAC strain suppresses phagocytosis of the M phi, which may allow extracellular spreading of such NO-resistant mycobacteria. Therefore, the pathogenic potential of MAC may be partly attributed to its resistance to NO.

In vitro activity of RP 74501-RP 74502, a novel streptogramin antimicrobial mixture, against clinical isolates of Legionella species

Agar and broth microdilution MICs of RP 74501-RP 74502, a mixture of streptogramin antimicrobial agents that inhibited 90% of 22 Legionella strains tested, were 0.64 and 0.08 microgram/ml, respectively; respective erythromycin values were 1.0 and 0.12 microgram/ml. RP 74501-RP 74502 at 1 microgram/ml was more active than the same erythromycin concentration in a macrophage system for both L. pneumophila strains studied but at a lower concentration (0.25 microgram/ml) was much less active than erythromycin.

Comparison of porcine alveolar macrophages and CL 2621 for the detection of porcine reproductive and respiratory syndrome (PRRS) virus and anti-PRRS antibody

The American and European strains of porcine reproductive and respiratory syndrome (PRRS) virus were initially isolated in an established cell line (CL 2621) and porcine alveolar macrophages (PAM), respectively. Subsequent isolation of American strains of this virus in PAM has also been reported. To determine their relative sensitivity for virus isolation, both PAM and CL 2621 cells were inoculated with 98 tissue specimens and 73 serum samples from animals suspected of having PRRS. Four of the 98 tissue samples yielded virus in both cell types, whereas 7 samples were positive only in PAM and 4 samples only in CL 2621. Of the 73 serum samples tested, 18 were positive in PAM of which only 2 were positive in CL 2621. Additionally, 82 isolates obtained initially in CL 2621 were inoculated in PAM cells, and 18 strains isolated originally in PAM were inoculated in CL 2621. Of the 82 CL 2621 isolates, 25 could not be propagated on PAM. Of the 57 that replicated in PAM, as detected by a positive test on indirect fluorescent antibody test, only 28 produced cytopathic effects and 29 did not. Of the 18 PAM isolates, 5 did not grow on CL 2621. Although PAM were relatively more sensitive for virus isolation, their failure to support the growth of certain strains of PRRS virus indicates the existence of variants among PRRS virus strains, and both PAM and CL 2621 should be used for virus isolation from clinical samples. In addition, the sensitivity of these 2 cell types was compared for the detection of fluorescent antibodies to PRRS virus using 179 serum samples from PRRS-infected animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Pneumocystis carinii induction of tumor necrosis factor-alpha by alveolar macrophages: modulation by pentamidine isethionate

Pneumocystis carinii, and the inflammatory response it provokes, together contribute to irreversible lung damage in immunocompromised patients. P. carinii cysts were found to be capable of inducing tumor necrosis factor-alpha (TNF) release from alveolar macrophages in a concentration-dependent manner. At physiologically achievable concentrations, pentamidine isethionate (pentamidine) substantially reduces such production. Pretreatment of alveolar macrophages (AM phi) with interferon-gamma (IFN-gamma) synergizes with P. carinii to produce increased levels of TNF, a condition which pentamidine was also able to antagonize. Pentamidine treatment did not interfere with the phagocytic ability of AM phi. Considering clinical reduction of TNF could lessen P. carinii pneumonia (PCP) induced inflammation, the efficacy of pentamidine in the treatment of PCP may be partially associated with its ability to inhibit the release of inflammatory mediators such as TNF.

Porcine epidemic abortion and respiratory syndrome (mystery swine disease). Isolation in Spain of the causative agent and experimental reproduction of the disease

In March of 1991, a disease that affected pregnant sows and caused a high mortality in unweaned piglets was detected in Spain. Based on the clinical signs observed, mystery swine disease, which had been described recently in Germany, Holland and Belgium, was suspected. From the samples obtained from the affected farm, a filtrable agent (0.22 micron) was isolated on cell culture. It produced cytopathic effects, its replication was intracytoplasmic, it was sensitive to chloroform, and cross-reacted with a Lelystad reference serum. When inoculated into pregnant sows, the agent produced inappetence for 2-4 days, without hyperthermia. One of the sows aborted at 100 days of gestation; the two others had delayed parturitions (days 115 and 116). There was a mixture of healthy piglets, mummified fetuses, stillbirths and weak piglets. Microscopic examination of the lungs of healthy piglets killed at 8 and 12 days of life revealed the presence of interstitial pneumonia. The sera from the three sows at 39 days after infection cross-reacted with the Lelystad virus (titres > or = 1/640), whereas pre-inoculation sera did not recognize it (titres < or = 1/10). This is the first report from Spain of the isolation of an agent (antigenically related to the Lelystad virus), capable of reproducing the disease previously designated as mystery swine disease.

Isolation of a Lelystad virus-like agent from British pigs and scanning electron microscopy of infected macrophages

Six, one-week-old gnotobiotic piglets were inoculated with tissues or sera collected from field cases of porcine reproductive and respiratory syndrome. The piglets showed little or no illness, and two that were necropsied at 8 and 9 days post infection appeared grossly normal. However, a Lelystad virus-like agent was isolated from most of the inoculated pigs using porcine alveolar macrophage cultures. Seroconversion to the Lelystad virus was observed and some animals developed microscopically detectable interstitial pneumonias. Scanning electron microscopy was used to study the in vitro cytopathic effect of the Lelystad virus on porcine alveolar macrophages.

In vitro activities of fleroxacin against clinical isolates of Legionella spp., its pharmacokinetics in guinea pigs, and use to treat guinea pigs with L. pneumophila pneumonia

The activities of fleroxacin against 22 clinical Legionella isolates were determined by agar and broth microdilution susceptibility testing. The fleroxacin MIC required to inhibit 90% of strains tested on buffered charcoal yeast extract agar medium supplemented with 0.1% alpha-ketoglutarate was 0.64 micrograms/ml and was 0.04 microgram/ml when testing was done with buffered yeast extract broth supplemented with 0.1% alpha-ketoglutarate. Fleroxacin (0.25 microgram/ml) reduced the bacterial counts of two L. pneumophila strains grown in guinea pig alveolar macrophages by 1 log10 CFU/ml, but regrowth occurred over a 3-day period; fleroxacin was significantly more active than erythromycin in this assay. Single-dose (10 mg/kg of body weight given intraperitoneally) pharmacokinetic studies performed in guinea pigs with L. pneumophila pneumonia revealed peak levels in plasma and lungs to be 3.3 micrograms/ml and 3.5 micrograms/g, respectively, at 0.5 h and 0.8 microgram/ml and 0.8 microgram/g, respectively, at 1 h. The half-life of the terminal phase of elimination from plasma and lung was approximately 2 h. All 17 infected guinea pigs treated with fleroxacin (10 mg/kg/day) for 2 days survived for 14 days post-antimicrobial therapy, as did all 16 guinea pigs treated with the same dose of fleroxacin for 5 days. Only 1 of 16 animals treated with saline survived. The animals treated with fleroxacin for 2 days lost more weight and had higher temperatures than those treated with the antibiotic for 5 days. Fleroxacin is effective against L. pneumophila in vitro and in a guinea pig model of Legionnaires' disease. Fleroxacin should be evaluated as a treatment for human Legionnaires' disease.

In vitro activity of Ro 23-9424 against clinical isolates of Legionella species

Agar and broth microdilution MICs of Ro 23-9424 that inhibited 90% of 22 Legionella clinical isolates tested were 0.64 and 0.08 micrograms/ml, respectively; respective erythromycin values were 1.0 and 0.12 micrograms/ml. Ro 23-9424 (1 microgram/ml) was slightly more active than the same erythromycin concentration in a macrophage system, for both Legionella pneumophila strains studied.

Binding of unopsonized Cryptococcus neoformans by human bronchoalveolar macrophages: inhibition by a large-molecular-size serum component

Infection with Cryptococcus neoformans usually begins after inhalation of airborne organisms. Since levels of opsonins in the alveolar space may be low, the ability of human bronchoalveolar macrophages to bind C. neoformans in the presence and absence of opsonins was studied. Bronchoalveolar macrophages bound unopsonized C. neoformans. Surprisingly, component(s) in pooled human serum (PHS) inhibited binding, as evidenced by 26% and 71% inhibition of binding when 20% PHS and heat-inactivated PHS (HI-PHS), respectively, were added to the system. Separation of PHS by molecular size revealed that the inhibitory component had an apparent molecular weight greater than 10(6) and was inhibitory at nanomolar concentrations. PHS stimulated and HI-PHS had no effect on binding of acapsular C. neoformans and zymosan particles to bronchoalveolar macrophages. These data demonstrate that bronchoalveolar macrophages can bind unopsonized, encapsulated C. neoformans, but that serum component(s) inhibits binding.

Effects of pseudorabies virus infection upon cytotoxicity and antiviral activities of porcine alveolar macrophages

Alveolar macrophages (AM) infected with Pseudorabies virus (PRV) were compared to noninfected AM for cytotoxicity against foreign or transformed cells and production of interferon (IFN). Five PRV strains were used to infect AM including strains that are known to be highly virulent for pigs, i.e. strain 4892 and strain S-62 as well as strains that are regarded as mild or nonvirulent, i.e. BUK and Bartha. The multiplicity of infection ranged from 0.005 to 0.05 TCID50/cell. The target cells in the cytotoxicity assays were either chicken red blood cells, PRV-infected vero cells, or human myeloblastoma cells (K562 cell line). For the production of IFN, AM cultures were treated with polyinosinic:polycytidylic acid (Poly I:C) diluted in tissue culture media at a concentration of 5 micrograms/10(6) cells. Culture supernatants were collected at various times poststimulation and tested for antiviral activity using the Vesicular Stomatitis Virus replication inhibition test. Swine AM were able to lyse chicken red blood cells in an antibody-independent way but not in an antibody-dependent way, whereas lysis of PRV-infected vero cells was accomplished both ways. The cytotoxicity against chicken red blood cells was reduced in the PRV-infected AM as compared to noninfected cells, particularly in AM infected with virulent PRV strains. Specific 51Cr release values for AM infected with S-62 and 4892 strains were 14 and 19, while the noninfected AM had values of 36. Similarly, in the antibody-dependent cytotoxicity assay against PRV-infected vero cells there was no activity of AM against K562 cells. The production of IFN was readily stimulated with Poly I:C. The optimal time for supernatant collection was between 12 and 16 h poststimulation. The antiviral activity was abrogated by treatment of the supernatant with antiserum against human leukocyte IFN; it was therefore considered to be due to interferon-alpha (IFN alpha) released from the macrophages. The antiviral activity present in supernatants of PRV-infected AM was reduced compared to noninfected AM. The difference between AM cultures infected with virulent strains of PRV and noninfected AM cultures was statistically significant at P < or = 0.025. The results provide support to the premise that the role of AM in lung defense can be compromised by PRV infection.

Markers of human immunodeficiency virus infection in pediatric bronchoalveolar lavage samples

Pulmonary cells and fluid obtained by bronchoalveolar lavage (BAL) from 19 pediatric acquired immunodeficiency syndrome (AIDS) patients with pneumonia were examined for markers of human immunodeficiency virus (HIV-1) infection. The HIV-1 DNA was detected in BAL cells by polymerase chain reaction (PCR) in 14 of 15 patients (93.3 percent). Immunostaining of cytocentrifuged cell preparations of six specimens revealed that HIV-1 antigen was associated with from five percent to 95 percent of the alveolar macrophages. Analysis of the 22 cell-free BAL fluids by enzyme immunoassay (EIA) showed that samples from three patients (15.8 percent) contained HIV-1 p24 antigen. One sample, with a dilution factor of 15.1 relative to serum, contained a markedly elevated antigen concentration (106 pg per ml) compared to the serum concentration (41.6 pg per ml). Antibodies to HIV-1 were present in the BAL fluids of six patients (31.6 percent) at levels detectable by EIA. By Western blot analysis, three samples yielded more intense gp120 bands compared to bands observed with matched serum samples. Our results suggest that HIV-1 and antibodies to this virus are frequently present in the lungs of children with AIDS and that the serum antigen and antibody profile of some patients does not reflect local pulmonary levels.

Stimulation and suppression of the oxygenation activity of porcine pulmonary alveolar macrophages by Actinobacillus pleuropneumoniae and its metabolites

The effects of Actinobacillus (Haemophilus) pleuropneumoniae and its metabolites on the oxygenation activity of porcine pulmonary alveolar macrophages (PAM) were studied, using a chemiluminescence technique. Actinobacillus pleuropneumoniae strains of serotypes 2, 3, and 9 in a dose of 1, 10, and 100 colony-forming units/macrophage first stimulated the oxygen radical production of PAM. After having reached a peak value, oxygenation activity decreased, finally resulting in total suppression of PAM. All these effects were neutralized by homologous convalescent pig sera that had been adsorbed onto inactivated A pleuropneumoniae strains. Moreover, cross-neutralization was shown between serotypes 2 and 3. Inactivated A pleuropneumoniae strains did not influence the oxidative activity of PAM. Undiluted and lower dilutions of sterile A pleuropneumoniae culture supernatants were toxic for PAM, whereas higher dilutions of the supernatants stimulated oxygen radical production of the macrophages. These effects were heat-sensitive and were neutralized by homologous convalescent pig sera. Cross-neutralization was shown between serotypes 2 and 3. These findings indicated that stimulation and inhibition of the oxygenation activity of PAM are attributable to heat-sensitive metabolites produced by A pleuropneumoniae.

Interaction of Mycoplasma dispar with bovine alveolar macrophages

The capacity to avoid phagocytosis and the activation of bovine alveolar macrophages (BAM) by encapsulated Mycoplasma dispar or purified M. dispar capsule was investigated. Encapsulated and unencapsulated M. dispar were cocultured with BAM in the presence or absence of antisera prepared against unencapsulated M. dispar or purified capsule antiserum. Unopsonized mycoplasmas resisted phagocytosis, while only anti-capsule antibodies enhanced the phagocytosis of encapsulated mycoplasmas. BAM were cultured in the presence of purified M. dispar capsule or either live or heat-killed encapsulated or unencapsulated M. dispar. These BAM were then activated with Escherichia coli endotoxin or left without further activation. The supernatants of these cultures were assayed for tumor necrosis factor, interleukin 1, and glucose consumption as indicators of macrophage activation. Tumor necrosis factor and interleukin 1 were produced by BAM stimulated with unencapsulated M. dispar but not when encapsulated M. dispar or its purified capsule was used. Similarly, glucose consumption was increased in the presence of unencapsulated M. dispar, but not when BAM were cocultured with encapsulated M. dispar or purified capsule. When BAM were treated with purified capsule or encapsulated mycoplasmas, they could not be subsequently activated by endotoxin. These results indicate that encapsulated M. dispar or purified capsule exerts an inhibitory effect on the activity of BAM and prevents the activation of these cells.

Anti-HIV-1 activity of 3'-azido-3'-deoxythymidine (AZT) in primary mononuclear phagocytes

Conflicting data have been reported on ability of 3'-azido-3'-deoxythymidine (AZT) to protect mononuclear phagocytes from HIV-1 infection. We compared the antiviral potency of AZT in three types of primary human mononuclear phagocytes: peripheral blood monocytes, monocyte-derived macrophages (in vitro differentiated) and alveolar macrophages (in vivo differentiated). To establish highly-productive virus infection, purified cells (greater than 99%) from healthy donors were challenged with the macrophage-tropic HTLV-IIIBa-L strain at input multiplicities ranging from 0.05 to 20 TCID50 per cell. AZT (0.1 nM-10 microM) was added immediately after infection and either continued for the duration of the experiment or stopped 1-7 days after infection. The kinetics of HIV-1Ba-L replication were assessed by measuring p24 antigen production on days 4-28 post-infection. Continuous treatment with AZT reproducibly inhibited viral replication in a concentration-dependent manner in all three cell types. The IC90 of AZT was 0.04 microM in blood monocytes, 0.009 microM in monocyte-derived macrophages, and 0.0001 microM in alveolar macrophages (mean of 3-4 donors for each cell type). AZT was not cytotoxic at less than 10 microM as assessed by cell viability, cell protein, and interferon-gamma-activated H2O2-release. In experiments in which AZT treatment was stopped after infection, viral replication resumed after a lag of 7-14 days and increased exponentially toward control levels. This occurred despite initial inhibition of virus production to below the limit of p24 detection (approximately 50 pg/ml). These results indicate that AZT is a potent inhibitor of HIV-1 replication in primary mononuclear phagocytes regardless of the stage of cell differentiation, and that AZT is most active in tissue (alveolar) macrophages. AZT does not irreversibly block infection of mononuclear phagocytes, however, as viral replication resumes after removal of AZT.

[The interaction of the causative agent of melioidosis with the host's alveolar macrophages]

Studies were carried out on guinea pigs and albino rats, intranasally infected with P. pseudomallei C-141. The cells of bronchovesicular exudate were obtained from animals 1, 4 and 24 hours after infection. Electron microscopy was applied to study the process of interaction of the agent and alveolar macrophages. Bacteria were shown to form a capsule which permitted avoiding phagocytosis, when entering the host respiratory system. Microbes that failed to form a capsule were absorbed by macrophages and enclosed in a phagosome. Then some bacteria were destroyed by the lysosomal enzymes, the other synthesized a capsule, which protected them against the effect of phagolysosome content. There were also such microbes which escaped from a phagosome prior to fusion with lysosomes and parasitized in phagocytic cytoplasma forming a capsule there. By the end of the first 24 hours of observation the intact encapsulated microbe species were found to prevail in the host cells.

Effects of two adenoviruses (type 1 and type 8) on functional properties of bovine alveolar macrophages in vitro

Cultures of bovine alveolar macrophages were inoculated with type-1 and type-8 adenoviruses, initially isolated from calves with respiratory tract disease, and functional properties of the cells were observed over a period of 10 to 11 days. Both viruses replicated in macrophages; viral titers were low (less than 3.75 log10 TCID50/0.1 ml), and intranuclear inclusions were detected by indirect immunofluorescence in 5 to 10% of the cells from 3 days after inoculation. Highest titers were induced by type-1 adenovirus, which also induced the greatest functional changes. Expression of Fc and complement receptors was reduced by both viruses, although the greatest effects were seen with type 1. Phagocytosis of Candida krusei cells was reduced following type 1 infection, whereas phagocytosis in type-8-infected cells was not different from that of noninfected macrophages. Ability to kill ingested Candida cells also was reduced following type-1 infection, whereas type-8-infected macrophages had lower killing ability only at 2 to 4 days after inoculation. Neither virus had substantial effects on the production of neutrophil chemotactic factors by the macrophages.

Persistent infection of human adenovirus type 5 in human monocyte cell lines

Adenovirus infection of human monocyte hybridoma cell lines and the fusion partner U937 was investigated. Adenovirus adsorbed poorly to these cells as well as primary human alveolar macrophages. The virus-binding experiments showed a 100-fold reduction in apparent viral binding to these cells compared to the permissive HeLa cells. Adsorption of adenovirus to these cells could be enhanced by preincubation of adenovirus with its antiserum. Following entry into the cells amplification of adenovirus DNA was detected starting at 2 days postinfection but few mature virus particles were produced. The infected cultures survived the infection and continued to grow for more than a year. In these chronically infected cultures, linear adenovirus DNA persisted up to 200 copies per cell and a small amount of mature virus was produced. Infectious center assay and cell cloning experiments showed that the majority of the cells in the chronically infected cultures harbor adenovirus genome. These results indicate that restriction of replication of human adenovirus type 5 at the late phase results in persistent infection of U937 and the human monocyte hybridoma cell lines.

Immunohistochemical observations on pneumonic lesions caused by Rhodococcus equi in foals

An immunohistochemical analysis of Rhodococcus equi-induced pneumonia in 10 foals was performed by biotin-streptavidin system. The detection of R. equi was more sensitive in immuno-stain using anti-R. equi serum than in Gram's stain. This bacteria also reacted to anti-BCG serum. Lysozyme and alpha 1-antitrypsin were detectable in macrophages. A particularly intense staining was observed in association with intracellular bacteria. Though a degree of reaction for alpha 1-antichymotrypsin was very low in comparison with lysozyme and alpha 1-antitrypsin, it was also demonstrated in macrophages ingesting R. equi. These bacteria were almost intact under an electron microscope. Therefore, the surface components of R. equi may play important roles of protection from intracellular enzymes of macrophages. The cells containing intracytoplasmic IgM, IgG or IgA were a few in number and scattered predominantly around the pneumonic lesion. It is considered that the bactericidal activity by immunoglobulins may be weak in comparison with phagocytosis by macrophages.

Role of the host cell nucleus in the replication of African swine fever virus DNA

An examination by autoradiography of African swine fever virus-infected alveolar macrophages pulse labeled with [3H]thymidine showed that, at early times of viral DNA replication, the grains were localized exclusively in the nucleus in 20% of the cells, while in 45% the label was found in the cytoplasm. In the remaining 35%, newly synthesized DNA was detected in both the nucleus and the cytoplasm. At later times, the percentage of cells with grains in the nucleus decreased considerably. Pulse-chase experiments indicated that the DNA synthesized in the nucleus is then transported to the cytoplasm. The presence of virus-specific DNA sequences in the nucleus was confirmed by in situ hybridization of infected macrophages. Similar hybridization experiments with African swine fever virus-infected VERO cells followed by confocal microscopy also indicated the existence of a nuclear stage in the localization of the viral DNA. These results suggest a mechanism for African swine fever virus DNA replication with an initial stage in the nucleus followed by a cytoplasmic phase. Specific nuclear forms associated with the hybridization signal have been observed in African swine fever virus-infected macrophages and VERO cells. The nuclear forms seen in macrophages are consistent with a mechanism for the egress of the viral DNA from the nucleus that involves initial budding at the nuclear membrane.