Effect of Haemophilus somnus on nitric oxide production and chemiluminescence response of bovine blood monocytes and alveolar macrophages

Haemophilus somnus is able to survive and multiply in bovine blood monocytes (BBM) and alveolar macrophages (BAM), but the mechanisms used by H. somnus to evade killing mechanisms of bovine mononuclear phagocytes are not completely understood. To study the bactericidal ability of bovine mononuclear phagocytes following interaction with H. somnus, in vitro assay systems were developed to detect the luminol-dependent chemiluminescence response (LDCL) and nitric oxide (NO) production of BBM and BAM. Live logarithmically growing or stationary phase H. somnus inhibited the LDCL of BBM and BAM costimulated with opsonized Staphylococcus aureus. Inhibition of the LDCL response of BBM and BAM was not mediated by live H. somnus opsonized with hyperimmune serum, or by killed bacteria. H. somnus stimulated both BBM and BAM to produce NO at levels comparable with Escherichia coli lipopolysaccharide. While NO was being produced, viable H. somnus could still be isolated from the cell cultures. The ability of H. somnus to inhibit LDCL of both BBM and BAM, and resistance to NO killing may be an important mechanism that contributes to survival of the organism following ingestion by bovine mononuclear phagocytes.

Reaction of human alveolar macrophages to exposure to Aspergillus fumigatus and inert particles

In vitro interaction of human alveolar macrophages (AM) with heat-killed conidia from Aspergillus fumigatus and inert silica particles of similar size, about 3 microns, was studied. The conidia were phagocytized significantly faster by AM than were the control particles partly due to the faster rate of attachment but especially due to the faster rate of ingestion. Quantitative nitroblue tetrazolium (NBT) reduction by AM, reflecting their release of oxygen radicals, was increased by a factor of 2 to 3 in response to the conidia during phagocytosis. The silica particles induced a moderate but significant increase in NBT reduction. Conidia, but not silica particles, showed a considerable percentage (around 8%) of phagolysosomes with neutral pH after 3 h and a smaller percentage (around 1%) after 24 h of incubation. The pH of phagolysosomes with conidia tended to be higher after 3 h, but was significantly lower after 24 h than the pH of phagolysosomes with silica particles. Despite the markedly increased oxidative metabolism there was no increase in cytokine production [interleukins (IL) 6 and 8 and tumor necrosis factor alpha (TNF-alpha)] after exposure to conidia. The silica particles induced a significant decrease in IL-6 and IL-8 production and a tendency toward decreased production of TNF-alpha. The occurrence of phagolysosomes with neutral pH suggests unsealed phagolysosomes from which not only oxygen metabolites but also enzymes might escape from the cell. Lung damage may thus be the result of repeated or long-term exposure to Aspergillus conidia.

Expression of functions by normal sheep alveolar macrophages and their alteration by interaction with Mycoplasma ovipneumoniae

Normal sheep alveolar macrophages collected by bronchial lavage were exposed to live or heat-killed Mycoplasma ovipneumoniae organisms, and their capability to ingest Staphylococcus aureus and to elicit antibody-dependent cellular cytotoxicity against sensitized chicken red blood cells was tested. Controls consisted of non-infected macrophages in M199 medium. In addition, the effect of M. ovipneumoniae on expression of surface molecules on these sheep alveolar macrophages was determined. The percentage of S. aureus ingested by nontreated sheep alveolar macrophages was significantly higher than that of infected macrophages. Live mycoplasmas were more effective in suppressing the ingestion of S. aureus by these macrophages than killed mycoplasmas. Both live and killed mycoplasmas suppressed the cytolytic effect of the sheep alveolar macrophages to a similar degree. About 78% and 45% of the normal sheep alveolar macrophages had IgG and complement receptors, respectively. Infection of these macrophages with M. ovipneumoniae decreased significantly the expression of IgG receptors but had no effects on complement receptors. There were substantial increases in the expression of both MHC class I and class II by the mycoplasma-induced macrophages as compared with unstimulated macrophages. Live mycoplasmas were more effective in inducing expression of both classes than killed mycoplasmas. The results, taken together, suggest that M. ovipneumoniae induced alterations in macrophage activities and this may be a contributing factor in the pathogenesis of respiratory disease induced by the organism.

Activity of KRM 1648 or rifabutin alone or in combination with clarithromycin against Mycobacterium avium complex in human alveolar macrophages

SETTING

The activity of KRM 1648 (KRM), a new benzoxazinorifamycin, and rifabutin (RBT), alone or in combination with clarithromycin (CLA), was evaluated against Mycobacterium avium complex (MAC) that multiplied in human alveolar macrophages (AM).

DESIGN

AM were recovered by bronchoalveolar lavage, incubated in RPMI 1640 medium with 10% human AB serum, infected with four strains of MAC (of non-acquired immune deficiency syndrome [AIDS] origin), and then treated with each drug alone or in combination. After incubation for 7 days, colony forming units in each well were counted on 7H10 agar.

RESULTS

Although concentrations between 0.2 microgram/ml and 20 micrograms/ml of both rifamycins showed clear dose-dependent activities against all MAC strains tested, only 20 micrograms/ml of each drug had modest bactericidal effect. In combination with 2.0 micrograms/ml of CLA, however, 0.2 microgram/ml of both drugs caused a bactericidal response against two of the four MAC strains examined.

CONCLUSION

According to this human alveolar macrophage model of MAC infection, KRM and RBT in combination with CLA was found to be a promising candidate against human pulmonary MAC infection, and deserves clinical evaluation.

Antibody-mediated depletion of tumor necrosis factor-alpha impairs pulmonary host defenses to Legionella pneumophila

Tumor necrosis factor-alpha (TNF-alpha) has been shown to stimulate the resistance of alveolar macrophages and neutrophils to Legionella pneumophila in vitro. To determine whether endogenous TNF-alpha is necessary for host defense against legionellosis in vivo, anti-TNF-alpha IgG or control IgG was administered to rats exposed to aerosolized L. pneumophila. Treatment with anti-TNF-alpha neutralized >90% of the intrapulmonary TNF-alpha response to infection, resulting in persistent pneumonitis and failure to clear L. pneumophila from the lungs. Depletion of TNF-alpha limited the recruitment of mononuclear cells to the lungs and resulted in a progressive increase in the proportion of alveolar macrophages that were infected; neutrophil recruitment and phagocytosis were not impaired. Both systemic and intrapulmonary IFN-gamma levels were significantly higher in rats depleted of TNF-alpha. These observations indicate that TNF-alpha is required for the prompt resolution of pneumonic legionellosis and point to a direct role for TNF-alpha in the activation of phagocytes.

Induction of interleukin-6 mRNA in rat alveolar macrophages by in vitro exposure to both Cryptococcus neoformans and anti-C. neoformans antiserum

Lewis rat alveolar macrophages (AM) were harvested and exposed in vitro to Cryptococcus neoformans to investigate the induction of inflammatory cytokines. AM in tissue culture wells were incubated with viable yeast cells of C. neoformans or the capsular polysaccharide, glucuronoxylomannan (GXM), with or without rabbit anti-C. neoformans antiserum. At 3, 6, 12 and 24 h, AM were washed, lyzed and total RNA was isolated. Using reverse transcription-PCR, the transcripts of cytokine genes were semi-quantified by comparison with constitutive transcripts. Incubation of AM with lipopolysaccharide, as positive control, induced elevated levels of the three transcripts measured: interleukin (IL)-1 alpha, IL-6 and tumour necrosis factor (TNF)-alpha. Under the same conditions, no obvious changes were observed in the levels of transcription of these cytokines by AM after exposure to several strains of C. neoformans. However, AM that were incubated with both the yeast cells and rabbit polyclonal antisera to C. neoformans manifested significantly increased levels of mRNA for IL-6, but not IL-1 alpha or TNF-alpha. This increased level of IL-6 mRNA was detectable after incubation for 6 or 12 h. Levels of transcription in AM were unaffected by exposure to normal rabbit serum, specific antiserum alone. GXM at concentrations of 10, 100 or 500 micrograms ml-1, or GXM and antiserum. Adsorption of the antiserum with heat-killed yeast cells of C. neoformans diminished its ability to induce IL-6 mRNA in combination with fresh, viable yeast cells. The induction of IL-6 mRNA by yeast cells and antiserum does not require intact complement. In the absence of complement, the rabbit antiserum served as a potent opsonin and markedly increased phagocytosis of C. neoformans by AM. These results indicate that antibody-opsonized C. neoformans are readily phagocytosed by rat AM, and that antibody-mediated phagocytosis may differ from complement-mediated phagocytosis in the subsequent stimulation of IL-6.

Activation of latent HIV-1 by Mycobacterium tuberculosis and its purified protein derivative in alveolar macrophages from HIV-infected individuals in vitro

Although Mycobacterium tuberculosis (MTB) and its purified protein derivative (PPD) induce HIV in cell lines that harbor latent HIV infection, it is not known whether similar activation of HIV in primary macrophages infected with HIV occurs. This possibility was examined using alveolar macrophages (AM) obtained by bronchoalveolar lavage of HIV-infected subjects with CD4 counts <200/microl. PPD induced transcription of HIV in AM from HIV-infected subjects by reverse transcription-polymerase chain reaction (RT-PCR). PPD and MTB infection also induced HIV production in AM from these HIV-infected patients, determined by HIV p24 enzyme-linked immunosorbent assay (ELISA). Viral production in AM required short periods of cell contact with allogeneic lymphocytes. HIV was only inducible, however, in AM from subjects with detectable HIV load (one to three copies of HIV DNA/1000 cells). Thus, MTB and its PPD can induce HIV in latently infected AM.

Surfactant protein A (SP-A) mediates attachment of Mycobacterium tuberculosis to murine alveolar macrophages

Attachment of Mycobacterium tuberculosis organisms to alveolar macrophages (AMs) is an essential early event in primary pulmonary tuberculosis. Surfactant protein A (SP-A) is a nonimmune opsonin present in the alveolar spaces that binds carbohydrate residues such as mannose. It was hypothesized that SP-A attaches to M. tuberculosis and serves as a ligand between M. tuberculosis and AMs. [125I]SP-A was found to bind to M. tuberculosis in a time- and [Ca2+]-dependent manner with a Kd of 1.9 x 10(-9) M and an apparent number of 6.3 x 10(2) SP-A binding sites/organism. Further, deglycosylated SP-A had minimal binding to M. tuberculosis, indicating that sugar moieties are important in this interaction. SP-A specifically binds to a 60-kD cell-wall protein from M. tuberculosis. SP-A-mediated attachment of 51Cr-labeled M. tuberculosis organisms to AMs is dependent on time, SP-A concentration, and Ca2+. M. tuberculosis attachment to murine AMs in the absence of SP-A was 12.8 +/- 0.9%; however, in the presence of 5 microg/ml SP-A the attachment increased to 38.6 +/- 2.9% (P < 0.001). SP-A-mediated attachment was significantly decreased from 38.6 +/- 2.9% to 18.7 +/- 3.3% (P < 0.05) in the presence of antihuman SP-A antibodies. When the attachment assay was repeated in the presence of alpha-methylene-D-mannosepyranosidase (mannosyl-BSA) and type V collagen, SP-A-mediated attachment decreased from 38.6 +/- 2.9% to 16.6 +/- 1.5% (P < 0.001) and 19.1 +/- 1.4% (P < 0.05), respectively. Further, deglycosylated SP-A had only a minimal effect on M. tuberculosis attachment to AMs. These data indicate that SP-A can mediate M. tuberculosis attachment to AMs, and suggest possible underlying mechanisms for this.

Murine macrophage elastolytic activity induced by Aspergillus fumigatusstrains in vitro: evidence of the expression of two macrophage-induced protease genes

The interaction between Aspergillus fumigatus conidia and murine macrophages of various origins was investigated. Cocultures were carried out between A. fumigatus strains and freshly isolated murine pulmonary alveolar macrophages or two murine macrophage cell-lines: murine alveolar cell-line MALU and murine astrocytoma cell-line J774. By measuring the variation of elastolytic activity in the coculture supernatants with two elastin substrates, we demonstrated that either viable or fixed A. fumigatus or C. albicans yeasts or nonspecific particles induced significant macrophage elastolytic activity. The effect of A. fumigatus supernatant or the purified A. fumigatus galactomannan suggested also the possible involvement of this polysaccharide in macrophage-protease gene expression, release, and activity in invasive aspergillosis. The effect of inhibitory compounds demonstrated the potential implication of a macrophagic metalloprotease and a macrophagic cysteine protease. RNA analysis allowed us to demonstrate the induction of expression of two macrophagic protease genes in stimulated macrophages. Two distinctive mechanisms appeared to be implicated in macrophage protease induction: nonspecific phagocytosis in the earliest times of the coculture and (or) specific galactomannan recognition after its gradual release by the mycelium.

Interaction between Cryptococcus neoformans and alveolar macrophages

Phagocytosis, oxidative metabolism and phagolysosomal pH of rat alveolar macrophages (AM) were studied at different points of time after challenge with Cryptococcus neoformans. Phagocytosis was evaluated using a fluorescent quenching technique which distinguishes between attached and ingested organisms. The nitroblue tetrazolium (NBT) test was used as an indirect measurement of the oxidative metabolism of the phagocytes. The pH of the phagolysosomes was measured using a cytofluorometric technique. Both the attachment and ingestion of serum opsonized C. neoformans by AM were slow during the first hours of incubation, but were considerable after 24 h. The oxidative metabolism of Am challenged with the yeast was insignificant during the first hour, but reached high levels after 24 h. Most phagolysosomes in AM with ingested cryptococci had a pH < 5.5. Our results indicate that these AM defence mechanisms, although poor during the first hours after exposure to the yeast, are of significance after 24 h. Thus, in the immunocompetent host the AM should prevent the dissemination of C. neoformans from the lungs.

Steady-state effects of vitronectin and fibronectin on the binding, uptake, and degradation of Pneumocystis carinii in rat alveolar macrophages

Pneumocystis carinii pneumonia remains a serious complication of immunodeficiency. Vitronectin (VN) and fibronectin (FN) accumulate in the lung during P. carinii infection and bind to the organism, thereby enhancing macrophage release of TNF alpha. It is not known whether VN and FN also regulate uptake and degradation of P. carinii by macrophage when present in concentrations similar to those in the lung during pneumonia. To address this, macrophages were cultured with 35S-radiolabeled P. carinii and organism binding, phagocytosis, and degradation determined in media alone (control), or in the presence of VN or FN (100 micrograms/ml each). Soluble VN and FN, in concentrations similar to those in the host, did not significantly affect binding uptake or degradation of P. carinii by alveolar macrophages. Thus, although VN and FN enhance macrophage activation during P. carinii pneumonia, phagocytosis of the organism is not increased by these host glycoproteins under steady-state conditions.

Epidemiology and virulence assessment of Salmonella dublin

Six strains of Salmonella dublin with distinct antimicrobial susceptibility patterns and/or plasmid profiles were repeatedly isolated from calves in a calf rearing facility. Three of the six strains were isolated from numerous calves during outbreaks of clinical salmonellosis while the other three were not. These strains were compared for their ability to adhere to and internalize in human intestinal epithelial cells (Caco-2) and in bovine alveolar macrophages (BAM), to survive in BAM, and to cause lethal infection in female BALB/c mice. All six strains of S. dublin demonstrated an ability to adhere to and internalize in both Caco-2 cells and in BAM. However, strain differences in the level of adhesion and/or internalization in Caco-2 cells and BAM were demonstrated. Most strains were able to persist but not proliferate in BAM. One outbreak-associated strain which readily attached and internalized in eukaryotic cells in vitro was avirulent to mice at the dose tested. The remaining five strains were virulent to mice. In vitro measures of virulence attributes were not clearly correlated with virulence among S. dublin strains measured either as prevalence in calves during outbreaks of disease or as mouse lethality. Also, there was no association between prevalence of strains in calves during outbreaks of clinical salmonellosis and lethality in mice.

Modulation of macrophage function for defence of the lung against Pseudomonas aeruginosa

Pseudomonas aeruginosa is a common respiratory tract pathogen in certain groups of compromised hosts, most notably those with cystic fibrosis. The pathogenicity of P. aeruginosa may depend in part upon its capacity to resist normal phagocytic cell clearance. We have recently shown that phagocytosis of P. aeruginosa by macrophages is a unique two-step process; binding is glucose-independent but ingestion occurs only in the presence of D-glucose or D-mannose. P. aeruginosa is the only particle we have found which is ingested by macrophages in a glucose-dependent manner. Since glucose is present in only negligible quantities in the endobronchial space, P. aeruginosa may be pathogenic by virtue of its capacity to exploit the opportunity presented in the lower airway to resist normal nonspecific phagocytic defences. The purpose of the studies reported here is to better understand the glucose-dependent phagocytosis of P. aeruginosa and to design novel therapies to facilitate phagocytic cell clearance of it from the lower respiratory tract. We have shown that phagocytosis of unopsonized P. aeruginosa depends upon facilitated transport of glucose into macrophages via the GLUT1 isoform. After transport into the macrophage, the glucose must be metabolized to trigger phagocytosis of P. aeruginosa; pretreatment with 2-deoxyglucose or 5-thioglucose abrogates glucose-dependent ingestion. We have recently demonstrated that pulmonary alveolar macrophages (as opposed to all other macrophage phenotypes studied) lack the capacity to transport glucose and to phagocytose unopsonized P. aeruginosa; however, after the cells have been cultured in vitro for 48 hours, they are able to perform both functions. Whereas most macrophages (such as peritoneal cells) primarily depend upon glycolysis for metabolic energy, pulmonary alveolar macrophages reside in a high oxygen tension environment and appear to utilize oxidative phosphorylation. Treatment of freshly explanted pulmonary alveolar macrophages with sodium azide (to poison oxidative respiration) dramatically enhances both glucose transport and glucose-dependent phagocytosis of P. aeruginosa. We are currently investigating the compromised phagocytic function of pulmonary alveolar macrophages and the mechanism by which azide enhances glucose transport and phagocytosis of P. aeruginosa. Although physiological measurements have indicated that glucose is removed from the endobronchial space by an active transport process of the lung epithelium, the types of glucose transporters that are expressed in the lung are as yet unknown. Using RT-PCR, we have amplified a product from human and murine lung RNA which has a high degree of homology with members of the sodium-dependent glucose transporter (SGLT) family. The ultimate goal of these studies is to design novel agents for enhancing the phagocytic function of pulmonary alveolar macrophages. Delivery of simple glucose by aerosol would not be effective because (i) it would be exported by sodium-dependent active transport and (ii) pulmonary alveolar macrophages lack the capacity to transport glucose. Various approaches for targeting glucose to alveolar macrophages by receptor-mediated endocytosis are under investigation.

Sequestration of Mycobacterium tuberculosis in tight vacuoles in vivo in lung macrophages of mice infected by the respiratory route

Following aerosol infection of mice with Mycobacterium tuberculosis, single mycobacteria or pairs of bacilli were observed within individual phagocytic vacuoles bound by tightly apposed vacuolar membranes. The virulent organism was not observed free in the cytoplasm of the parasitized cells or in the extracellular space of the lung granulomata. This study indicates that in vivo, virulent mycobacteria survive and probably replicate within a unique tight vacuole in the infected phagocyte within the lung.

Modulation of phagocytic function of bovine mononuclear phagocytes by Haemophilus somnus

The interactions between bovine mononuclear cells and Haemophilus somnus are known to be complex. To study this interaction, a flow cytometric assay was developed to assess the effect of H. somnus on phagocytosis of killed opsonized Staphylococcus aureus by bovine alveolar macrophages and blood monocytes. Using this in vitro system, it was found that log phase H. somnus significantly inhibited the phagocytosis of killed opsonized S. aureus by bovine alveolar macrophages obtained both from healthy calves and from cattle experimentally infected with H. somnus. However, killed log-phase H. somnus, in vitro passaged and stationary phase H. somnus had no effect on the phagocytic activity of these cells. In contrast to bovine alveolar macrophages, blood monocytes showed a significant increase in their phagocytic activity following in vitro exposure to either log or stationary phase H. somnus. Using a lypophilic, non-toxic fluorophore PKH2 to label live H. somnus, it was possible to simultaneously measure the uptake of both S. aureus and H. somnus. Stationary and log phase H. somnus were taken up by macrophages equally well, even though phagocytosis of S. aureus was inhibited by only log phase H. somnus. These results demonstrate the ability of H. somnus to modulate bovine mononuclear phagocytic function which might contribute towards the pathogenesis of bovine hemophilosis.

Infection by Mycobacterium tuberculosis promotes human alveolar macrophage apoptosis

The effect of Mycobacterium tuberculosis infection on the viability of healthy (control) human alveolar macrophages was evaluated by staining with ethidium homodimer and calcein to discriminate live from dead cells. Infection with M. tuberculosis H37Ra or H37Rv increased macrophage mortality at 6 days from the control level of 3.8% +/- 0.7% to 28.7% +/- 6.9% or 12.6% +/- 3.1%, respectively (P < 0.001 for comparisons of all conditions). A role for tumor necrosis factor alpha (TNF-alpha) in the M. tuberculosis-induced cytolysis of alveolar macrophages was demonstrated by increased cytotoxicity following the addition of exogenous TNF-alpha to the cultures and by enhancement of macrophage survival when M. tuberculosis-infected alveolar macrophages were treated with pentoxifylline or anti-TNF-alpha antibody. The cytolytic mechanism was determined to be apoptosis by the demonstration of a characteristic internucleosomal ladder of genomic DNA by agarose gel electrophoresis, by finding nuclear fragmentation and condensation by electron microscopy, and by in situ terminal transferase-mediated nick end labeling of fragmented DNA in alveolar macrophages infected with M. tuberculosis in vitro. The latter technique was employed to reveal extensive apoptosis within caseating granulomas from lung tissue samples from clinical tuberculosis cases. The induction of apoptosis in alveolar macrophages by M. tuberculosis may play a role in the macrophage-pathogen interaction of tuberculosis in vivo.

An oxaloacetate decarboxylase homologue protein influences the intracellular survival of Legionella pneumophila

Legionella pneumophila is a facultative intracellular parasite which is able to survive in various eukaryotic cells. We characterised a Tn5-mutant of the L. pneumophila Corby strain and were able to identify the insertion site of the transposon. It is localised within an open reading frame which shows high homology to the alpha-subunit of the oxaloacetate decarboxylase (OadA) of Klebsiella pneumoniae. The OadA homologous protein of L. pneumophila was detected in the wild-type strain by Western blotting. Since the intracellular multiplication of the oadA- mutant strain is reduced in guinea pig alveolar macrophages and human monocytes, it is concluded that the oadA gene product has an effect on the intracellular survival of L. pneumophila.

Differential and strain-specific triggering of bovine alveolar macrophage effector functions by mycoplasmas

Mycoplasma strains being considered as pathogenic or non-pathogenic for cattle were tested on their capacity to activate bovine alveolar macrophages in vitro. Of particular interest was the behaviour of Mycoplasma mycoides ssp. mycoides small colony type (M.m.m. SC), the causative agent of contagious bovine pleuropneumonia (CBPP). Increases in procoagulant activity (PCA), tumor necrosis factor-alpha- (TNF-alpha) and nitrogen monoxide (NO) generation were tested. To minimize an influence of macrophage activation by mycoplasma growth media, mycoplasmas were cultured on embryonic calf nose epithelial cells. The three macrophage functions tested were not correlated, but were differentially induced in strain-specific manner. Four out of seven strains induced PCA, regardless of pathogenicity, and all strains promoted moderate NO generation at high concentrations. All tested M.m.m. SC strains (Afadé, L2 and PG1), and the pathogenic M. bovis, induced TNF-alpha production at low concentrations (10(6) colony forming units per ml). M.sp. serogroup 7 and the non-pathogenic M. bovirhinis and Acholeplasma laidlawii did not induce TNF-alpha up to 10(8) cfu/ml. Thus, strain-specific differences are reflected in differential macrophage activation patterns. The findings are consistent with an important role for TNF-alpha in pathogenesis of CBPP.

Cavitary tuberculosis produced in rabbits by aerosolized virulent tubercle bacilli

Liquefaction of solid caseous tuberculous lesions and the subsequent cavity formation are probably the most dangerous processes in the pathogenesis of human pulmonary tuberculosis. In liquefied caseum, the tubercle bacilli grow extracellularly for the first time since the onset of the disease and can reach such large numbers that mutants with antimicrobial resistance may develop. From a cavity, the bacilli enter the bronchial tree and spread to other parts of the lung and also to other people. Of the commonly used laboratory animals, the rabbit is the only one in which cavitary tuberculosis can be readily produced. This report is the first to describe and analyze the complete course of cavitary tuberculosis, produced by aerosolized virulent bovine-type tubercle bacilli in commercially available New Zealand white rabbits. After the inhalation of 220 to 880 bacillary units, all of the rabbits were overtly well until they were sacrificed at 33 weeks. After the inhalation of 3,900 to 5,800 bacillary units, half of the rabbits died of progressive tuberculosis between 5 and 9 weeks and the other half lived until they were sacrificed at 18 weeks. Pulmonary cavities developed in both low- and high-dose groups, some beginning as early as 6 weeks. Bacilli from primary cavities sometimes caused nearby secondary cavities, but more frequently, they ascended the bronchial escalator, were swallowed, and caused secondary tubercles in the lymphoid tissue of the appendix and ileocecal junction. Histologically, and by culture, the number of bacilli found in the liquefied caseum varied from many to comparatively few. Strong tuberculin reactions at 4 weeks after infection were associated with fewer primary lesions, while strong tuberculin reactions at 33 weeks were associated with more cavitary lesions. In the tuberculous granulation tissue surrounding caseous and liquefied pulmonary foci and cavities, we found many mature epithelioid macrophages that contained high levels of the proteinase cathepsin D. Therefore, cathepsin D probably plays a major role in the liquefaction of solid caseous material and in the subsequent cavity formation.

Candida albicans adherence to a human oesophageal cell line

The oesophageal epithelium appears to be one of the primary cell targets of Candida albicans in AIDS patients. To study this interaction, we have established an in vitro adherence assay using a human epithelial oesophageal cell line (HET1-A). When yeast cells were grown in 500 mM D-galactose, adherence increased significantly over cultures prepared in 500 mM D-glucose. In addition to HET1-A cells, adherence of the organism grown in D-galactose to human buccal epithelial cells and a murine alveolar macrophage cell line was also higher. Adherence of yeast cells to HET1-A cells was partially inhibited in the presence of D-glucosamine or N-acetyl-D-glucosamine, but not with D-mannose, D-glucose, L-fucose or D-galactose. Attachment to HET1-A cells was studied using scanning and transmission electron microscopy. Partial phagocytosis of adhering yeast cells was observed occasionally within the first 90 min following infection, as evidenced by the formation of HET1-A pseudopodia in instances of close contact with yeast cells. The influence of D-galactose on cell surface proteins was studied by analysing beta-mercaptoethanol-extracted proteins from yeast cells grown in either 500 mM D-galactose or D-glucose. From D-galactose-grown cells only, a glycoprotein of approximately 190 kDa was observed in Aurodye-stained SDS-PAGE gels and in Western blots using an immunoglobulin fraction (IgG) prepared from sera of rabbits infected with the organism. These studies demonstrate that C. albicans adheres to human oesophageal cells and may utilize cell surface proteins whose synthesis is nutritionally regulated.

IL-10 enhances the growth of Legionella pneumophila in human mononuclear phagocytes and reverses the protective effect of IFN-gamma: differential responses of blood monocytes and alveolar macrophages

Legionella pneumophila is a facultative intracellular pathogen that parasitizes human alveolar macrophages and blood monocytes recruited to the lungs. The inhibitory cytokines IL-10, TGF-beta, and IL-4 generally deactivate macrophages and permit enhanced microbial growth in some models of intracellular infection, but their effects on human alveolar macrophages are unknown. We hypothesized that inhibitory cytokines could facilitate the infection of human alveolar macrophages and monocytes by virulent intracellular lung pathogens. Therefore, we tested the effects of IL-10, TGF-beta, and IL-4 in an in vitro model of human alveolar macrophage and monocyte infection with L. pneumophila. We found that unstimulated alveolar macrophages supported over 100-fold greater L. pneumophila growth than did unstimulated monocytes. IL-10 treatment significantly enhanced L. pneumophila growth in monocytes, and completely reversed the protective effect of IFN-gamma against intracellular L. pneumophila replication. IL-10 had similar but less potent effects on alveolar macrophages. In contrast, TGF-beta and IL-4 had no significant effects on L. pneumophila growth in resting or IFN-gamma-activated monocytes or alveolar macrophages. IL-10 blocked TNF-alpha production by infected cells, but exogenous TNF-alpha did not reverse the activating defect in cells cocultured with IFN-gamma and IL-10. Finally, L. pneumophila-infected monocytes produced substantially more IL-10 than did infected alveolar macrophages. In summary, IL-10 significantly enhances the growth of L. pneumophila in human monocytes, reverses the protective effect of IFN-gamma, blocks TNF-alpha secretion, and is secreted by infected monocytes and alveolar macrophages. Induction of IL-10 may be a virulence mechanism that promotes intracellular bacterial replication in human legionellosis.

Adherence of Mycoplasma pneumoniae to human alveolar macrophages

The human pathogen Mycoplasma pneumoniac causes primary atypical-cold agglutinin-positive pneumonia. Since alveolar macrophages internalize mycoplasma as part of their immune defense, we studied characteristics of the human macrophage receptor for opsonized and nonopsonized M. pneumoniae. The glass-adhering subpopulation of M. pneumoniae attached more than the non-adherent subpopulation. The attachment was dose-dependent and enhanced by opsonization in the presence of human serum. It is inhibited by sulfated compounds such as dextran-sulfate and polyanetholsulfonic acid, but not by dextran or several monosaccharides, suggesting that sulfated glycolipids on the macrophage surface may act as receptors for M. pneumoniae binding. In addition, sialylated compounds, such as fetuin and alpha 1-acid glycoprotein, were found to be potent inhibitors of the attachment, also indicating the role of sialic acid residue in recognition and attachment of M. pneumoniae to human alveolar macrophages.

Differential infection of porcine alveolar macrophage subpopulations by nonopsonized Mycobacterium bovis involves CD14 receptors

The resurgence in mycobacterial infection worldwide has led to renewed attention to the pathogenesis of Mycobacterium species. The purpose of this study was to characterize the infection of alveolar macrophages (AMs) by nonopsonized Mycobacterium bovis, and to elucidate the mechanism by which a differential infection of subpopulations of AM may occur. A difference in susceptibility to Mycobacterium bovis infection of subpopulations of AMs was observed, such that the least dense cells were the least susceptible (21.4 +/- 10.7%) and the most dense cells were the most readily infected (61.8 +/- 5.6%). The percentage of AMs staining for CD14 receptors showed a similar differential distribution, with fewer of the least dense cells expressing CD14 and a greater percentage of the most dense cells staining for CD14 receptor expression. To investigate the role of CD14 receptors in the infection of AMs, anti-CD14 antibody was added to the cell cultures. Infection of AM by Mycobacterium bovis was blocked by up to 60.2% by anti-CD14 antibody but not by isotype control antibody. The results of this study suggest that Mycobacterium bovis selectively infects AM subpopulations, specifically those with the greatest expression of CD14, a putative receptor mechanism for Mycobacterium bovis infection of porcine AM.

The Salmonella virulence plasmid enhances Salmonella-induced lysis of macrophages and influences inflammatory responses

The Salmonella dublin virulence plasmid mediates systemic infection in mice and cattle. Here, we analyze the interaction between wild-type and plasmid-cured Salmonella strains with phagocytes in vitro and in vivo. The intracellular recovery of S. dublin from murine peritoneal and bovine alveolar macrophages cultured in the presence of gentamicin in vitro was not related to virulence plasmid carriage. However, the virulence plasmid increased the lytic activity of S. dublin, Salmonella typhimurium, and Salmonella choleraesuis for resident or activated mouse peritoneal macrophages. Lysis was not mediated by spv genes and was abolished by cytochalasin D treatment. Peritoneal and splenic macrophages were isolated from mice 4 days after intraperitoneal infection with wild-type or plasmid-cured S. dublin strains. The wild-type strain was recovered in significantly higher numbers than the plasmid-cured strain. However, the intracellular killing rates of such cells cultured in vitro for both S. dublin strains were not significantly different. Four days after infection, there was a lower increase of phagocyte numbers in the peritoneal cavities and spleens of mice infected with the wild-type strain compared with the plasmid-cured strain. The virulence plasmid influenced the survival of macrophages in vitro following infection in vivo as assessed by microscopy. Cells from mice infected with the plasmid-cured strain survived better than those from mice infected with the wild-type strain. This is the first report demonstrating an effect of the virulence plasmid on the interaction of Salmonella strains with macrophages. Plasmid-mediated macrophage dysfunction could influence the recruitment and/or the activation of phagocytic cells and consequently the net growth of Salmonella strains during infection.