Differences in virulence for mice among strains of Mycoplasma pulmonis

An attenuated multiple genetic mutant of Mycoplasma pneumoniae imparts good immuno-protection against M. pneumoniae pneumonia in BALB/c mice

Mycoplasma pneumoniae (M. pneumoniae) is the causative agent of both upper and lower respiratory infections that can lead to pneumonia, extrapulmonary complications and devastating sequela. With the increasing rate of macrolide-resistant strains, the severe clinical consequence of refractory mycoplasma pneumonia in children health calls for the need of vaccine research for this pathogen. In this report, the immunomodulatory effectiveness of a live attenuated M. pneumoniae vaccine was evaluated. The vaccine strain was a mutant strain of M. pneumoniae, MUT129, obtained after multiple passages of M129 strain in PPLO broth. The SNP/InDel detection results showed that mutations were present in genes encoding the adhesion organelle-associated proteins and lipoproteins of M. pneumoniae MUT129. Upon intranasal challenge of BALB/c mice with 1 × 10⁷ CFU of MUT129, there were very small amount of Mycoplasma antigens and almost no M. pneumoniae present in the lung tissues of BALB/c mice. Besides, there was almost no inflammatory cell infiltration in the lung tissue. Results of the M. pneumoniae challenge study showed that mice immunized with MUT129 presented with less inflammation, lower detectable number of M. pneumoniae in the lungs when compared with the unimmunized mice. These results indicated that the live attenuated vaccine can efficiently prevent the proliferation of M. pneumonia in the lungs, reduce but not completely prevent the pulmonary inflammatory response.

Profiling of cellular immune responses to Mycoplasma pulmonis infection in C57BL/6 and DBA/2 mice

Mycoplasma infections cause respiratory tract damages and atypical pneumonia, resulting in serious problems in humans and animals worldwide. It is well known that laboratory inbred mouse strains show various susceptibility to Mycoplasma pulmonis (M. pulmonis) infection, which causes murine respiratory mycoplasmosis. In this study, we aimed to demonstrate the difference in cellular immune responses between resistant strain, C57BL/6NCrSlc (B6) and susceptible strain, DBA/2CrSlc (D2) after challenging M. pulmonis infection. D2 mice showed higher amount of bacterial proliferation in lung, higher pulmonary infiltration of immune cells such as neutrophils, macrophages, and lymphocytes, and higher levels of interleukin (IL)-1β, IL-6, IL-17A, and tumor necrosis factor-α in bronchoalveolar lavage fluid than did B6 mice. The results of this study suggest that D2 mice are more susceptible than B6 mice to M. pulmonis infection due to a hyper-immune inflammatory response.

Interleukin-17A Exacerbates Disease Severity in BALB/c Mice Susceptible to Lung Infection with Mycoplasma pulmonis

Mycoplasmas are atypical bacteria that disrupt the immune response to promote respiratory tract infections and secondary complications. However, not every immunologic response that protects or damages the host during mycoplasma infection is known. Interleukin-17A (IL-17A) is elevated in individuals infected with mycoplasmas, but how IL-17A and its cellular sources dictate disease outcome remains unclear. Here, IL-17A is hypothesized to worsen disease in individuals susceptible to mycoplasma infection. Thus, monoclonal anti-IL-17A antibodies were given to disease-susceptible BALB/c mice and disease-resistant C57BL/6 mice infected with Mycoplasma pulmonis Neutralizing the function of IL-17A using anti-IL-17A antibodies reduced disease severity during M. pulmonis infection in BALB/c, but not C57BL/6, mice. Neutralizing IL-17A also reduced the incidence of neutrophilic lung lesions during infection in BALB/c mice. Reduced pathology occurred without impacting the bacterial burden, demonstrating that IL-17A is not required for mycoplasma clearance. The main source of IL-17A throughout infection in BALB/c mice was CD4⁺ T cells, and neutralizing IL-17A after infiltration of the lungs by T cells reduced disease severity, identifying the Th17 response as a herald of late mycoplasma pathology in susceptible mice. Neutralizing IL-17A did not further reduce disease during M. pulmonis infection in BALB/c mice depleted of neutrophils, suggesting that IL-17A requires the presence of pulmonary neutrophils to worsen respiratory pathology. IL-17A is a pathological element of murine respiratory mycoplasma infection. Using monoclonal antibodies to neutralize IL-17A could reduce disease severity during mycoplasma infection in humans and domesticated animals.

Regulatory CD4+CD25+ T Cells Dampen Inflammatory Disease in Murine Mycoplasma Pneumonia and Promote IL-17 and IFN-γ Responses

Mycoplasmas cause respiratory diseases characterized by persistent infection and chronic airway inflammation. Mycoplasma lung disease is immunopathologic, with CD4⁺ Th cells determining both disease severity and resistance to infection. Th2 cell responses promote immunopathology, while Th1 cells confer resistance to infection. However, regulatory CD4⁺ T cells may also have a role in the pathogenesis of mycoplasma respiratory diseases. We hypothesized Treg cells control the severity of the inflammatory lesions and may also promote persistence of infection. To examine this, BALB/c mice were depleted of CD25⁺ cells, and had increased disease severity due to Mycoplasma pulmonis infection. Increases in mycoplasma antibody responses and lymphocyte infiltration into lungs also occurred after CD25⁺ cell depletion. CD4⁺CD25⁺ regulatory T cells promoted IFN-γ and IL-17 mycoplasma-specific CD4⁺ T cell responses in vitro and in vivo, while dampening IL-13⁺ Th responses. Neither IL-10 nor TGF-ß expression was detected in CD4⁺CD25⁺ T cells from lymph nodes. Thus, a regulatory T cell population plays an important role in controlling damaging immune responses in mycoplasma respiratory disease but does not contribute to persistence of infection. It appears that a regulatory T cell population preferentially dampens Th2 cell-mediated inflammatory responses to mycoplasma through a mechanism independent of IL-10 or TGF-ß characteristic of “classic” Treg cells.

Development of an ELISA using a recombinant P46-like lipoprotein for diagnosis of Mycoplasma pulmonis infection in rodents

Mycoplasma pulmonis is one of the most prevalent bacterial pathogens that infects laboratory mice and rats. To develop an M. pulmonis-specific antigen for serological diagnosis, we cloned the cDNA of P46-like lipoprotein (P46L), an M. pulmonis putative periplasmic protein. P46L is a homolog of P46, an M. hyopneumoniae antigen. We produced recombinant P46L fused to glutathione S-transferase (GST) in Escherichia coli. Immunoblot analysis revealed that sera from Mycoplasma-infected mice and rats contained anti-P46L antibodies. We developed an ELISA using the recombinant P46L-GST protein as an antigen. Thirteen of the 14 samples from rats naturally infected with M. pulmonis were determined to be positive according to the commercial ELISA (MONILISA Myco) and positive by our ELISA. Furthermore, 18/19 samples from mice experimentally infected with M. pulmonis were positive using our P46L-GST ELISA. In contrast, only 8/19 samples from infected mice were positive by the commercial ELISA. Our results indicate that P46L-GST was an appropriate antigen for developing a serological test to determine M. pulmonis infection in laboratory mice and rats.

Type 1 and type 2 strains of Mycoplasma pneumoniae form different biofilms

Several mycoplasma species have been shown to form biofilms that confer resistance to antimicrobials and which may affect the host immune system, thus making treatment and eradication of the pathogens difficult. The present study shows that the biofilms formed by two strains of the human pathogen Mycoplasma pneumoniae differ quantitatively and qualitatively. Compared with strain UAB PO1, strain M129 grows well but forms biofilms that are less robust, with towers that are less smooth at the margins. A polysaccharide containing N-acetylglucosamine is secreted by M129 into the culture medium but found in tight association with the cells of UAB PO1. The polysaccharide may have a role in biofilm formation, contributing to differences in virulence, chronicity and treatment outcome between strains of M. pneumoniae. The UAB PO1 genome was found to be that of a type 2 strain of M. pneumoniae, whereas M129 is type 1. Examination of other M. pneumoniae isolates suggests that the robustness of the biofilm correlates with the strain type.

Dendritic cells are the major antigen presenting cells in inflammatory lesions of murine Mycoplasma respiratory disease

Mycoplasmas cause chronic respiratory diseases in animals and humans, and to date, development of vaccines have been problematic. Using a murine model of mycoplasma pneumonia, lymphocyte responses, specifically T cells, were shown to confer protection as well as promote immunopathology in mycoplasma disease. Because T cells play such a critical role, it is important to define the role of antigen presenting cells (APC) as these cells may influence either exacerbation of mycoplasma disease pathogenesis or enhancement of protective immunity. The roles of APC, such as dendritic cells and/or macrophages, and their ability to modulate adaptive immunity in mycoplasma disease are currently unknown. Therefore, the purpose of this study was to identify individual pulmonary APC populations that may contribute to the activation of T cell responses during mycoplasma disease pathogenesis. The present study indeed demonstrates increasing numbers of CD11c⁻ F4/80⁺ cells, which contain macrophages, and more mature/activated CD11c⁺ F4/80⁻ cells, containing DC, in the lungs after infection. CD11c⁻ F4/80⁺ macrophage-enriched cells and CD11c⁺ F4/80⁻ dendritic cell-enriched populations showed different patterns of cytokine mRNA expression, supporting the idea that these cells have different impacts on immunity in response to infection. In fact, DC containing CD11c⁺ F4/80⁻ cell populations from the lungs of infected mice were most capable of stimulating mycoplasma-specific CD4⁺ Th cell responses in vitro. In vivo, these CD11c⁺F4/80⁻ cells were co-localized with CD4⁺ Th cells in inflammatory infiltrates in the lungs of mycoplasma-infected mice. Thus, CD11c⁺F4/80⁻ dendritic cells appear to be the major APC population responsible for pulmonary T cell stimulation in mycoplasma-infected mice, and these dendritic cells likely contribute to responses impacting disease pathogenesis.

Pericyte requirement for anti-leak action of angiopoietin-1 and vascular remodeling in sustained inflammation

Blood vessel leakiness is an early, transient event in acute inflammation but can also persist as vessels undergo remodeling in sustained inflammation. Angiopoietin/Tie2 signaling can reduce the leakiness through changes in endothelial cells. The role of pericytes in this action has been unknown. We used the selective PDGF-B-blocking oligonucleotide aptamer AX102 to determine whether disruption of pericyte-endothelial crosstalk alters vascular leakiness or remodeling in the airways of mice under four different conditions: i) baseline, ii) acute inflammation induced by bradykinin, iii) sustained inflammation after 7-day infection by the respiratory pathogen Mycoplasma pulmonis, or iv) leakage after bradykinin challenge in the presence of vascular stabilization by the angiopoietin-1 (Ang1) mimic COMP-Ang1 for 7 days. AX102 reduced pericyte coverage but did not alter the leakage of microspheres from tracheal blood vessels at baseline or after bradykinin; however, AX102 exaggerated leakage at 7 days after M. pulmonis infection and increased vascular remodeling and disease severity at 14 days. AX102 also abolished the antileakage effect of COMP-Ang1 at 7 days. Together, these findings show that pericyte contributions to endothelial stability have greater dependence on PDGF-B during the development of sustained inflammation, when pericyte dynamics accompany vascular remodeling, than under baseline conditions or in acute inflammation. The findings also show that the antileakage action of Ang1 requires PDGF-dependent actions of pericytes in maintaining endothelial stability.

Angiopoietin-2-driven vascular remodeling in airway inflammation

Vascular remodeling is a feature of chronic inflammation during which capillaries transform into venules that expand the region of the vasculature in which leakage and leukocyte emigration both occur. Recently, we found that angiopoietin/Tie2 receptor signaling drives the transformation of capillaries into venules at an early stage of the sustained inflammatory response in the airways of mice infected with Mycoplasma pulmonis. However, the precise contributions of both angiopoietin-1 (Ang1) and angiopoietin-2 (Ang2) are not clear. In this study, we sought to determine the contribution of Ang2 to this vascular remodeling. Ang2 mRNA expression levels increased and phosphorylated Tie2 immunoreactivity in mucosal blood vessels decreased, indicative of diminished receptor signaling after infection. Selective inhibition of Ang2 throughout the infection by administration of either of two distinct function-blocking antibodies reduced the suppression of Tie2 phosphorylation and decreased the remodeling of mucosal capillaries into venules, the amount of leukocyte influx, and disease severity. These findings are consistent with Ang2 acting as an antagonist of Tie2 receptors and the reduction of Tie2 phosphorylation in endothelial cells rendering the vasculature more responsive to cytokines that promote both vascular remodeling and the consequences of inflammation after M. pulmonis infection. By blocking such changes, Ang2 inhibitors may prove beneficial in the treatment of sustained inflammation in which vascular remodeling, leakage, and leukocyte influx contribute to its pathophysiology.

Identification of compositionally distinct regions in genomes using the centroid method

MOTIVATION

It is known that most genomic regions of special interest, e.g. horizontally acquired sequences, genomic islands, etc. have distinct word (m-mer) compositions. Most of the earlier work along this direction, addressed di- and tri-nucleotide compositions. We present an approach that can be applied to analyze compositions of any given word size. The method, called the centroid approach, can reveal compositionally distinct regions in genomic sequences for any given word size.

RESULTS

We applied our method to 50 bacterial genomes and demonstrated its ability to identify embedded sequences of varying lengths from distantly related organisms. We also investigated the genetic makeup of the regions identified as compositionally distinct by our method, for four organisms from our dataset. Pathogenicity island (PAI) components and genes encoding strain-specific proteins are all frequently seen to be constituents of these regions.

AVAILABILITY

Program is available on request from the authors.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Surfactant dysfunction in SP-A-/- and iNOS-/- mice with mycoplasma infection

Surfactant dysfunction was studied in C57BL/6 (B6), B6.SP-A(-/-), and B6.iNOS(-/-) mice with pulmonary mycoplasma infection (10(7) colony-forming units). Cell-free bronchoalveolar lavage (BAL) from uninfected B6.SP-A(-/-) versus B6 mice had a reduced content of very large aggregates (VLA) and an increase in intermediate large aggregates (ILA), with no difference in total large aggregates (LA = VLA + ILA). However, LA from uninfected B6.SP-A(-/-) versus B6 mice contained less protein and were more sensitive to inhibition by serum albumin and lysophosphatidylcholine in pulsating bubble studies in vitro. Infection with Mycoplasma pulmonis caused significant lung injury and surfactant abnormalities in B6.SP-A(-/-), B6.iNOS(-/-), and B6 mice at 24, 48, 72 h after infection compared with uninfected mice of the same strain. Analyses of time-pooled data indicated that mycoplasma-infected B6.SP-A(-/-) and B6.iNOS(-/-) mice had significantly lower levels of LA and higher protein/phospholipid ratios in BAL compared with infected B6 mice. Infected B6.iNOS(-/-) versus B6 mice also had increased minimum surface tensions on the pulsating bubble and decreased levels of surfactant protein (SP)-B in BAL. These results indicate that pulmonary mycoplasma infection in vivo causes lung injury and surfactant abnormalities that are dependent in part on iNOS and SP-A. In addition, SP-A deficiency modifies surfactant aggregate content and lowers the inhibition resistance of LA surfactant in vitro compared with congenic normal mice.

Reactive species mediate inhibition of alveolar type II sodium transport during mycoplasma infection

RATIONALE

Mycoplasma pneumoniae is a significant cause of pneumonia in humans.

OBJECTIVES

To determine the impact of mycoplasma infection and the host inflammatory response on alveolar type II (ATII) cell ion transport in vivo and in vitro.

METHODS

Mice were infected with M. pulmonis for measurements of alveolar fluid clearance (AFC) in vivo and isolation of ATII cells. ATII cells were infected in vivo for determination of epithelial Na+ channel (ENaC) total and cell surface protein levels by biotinylation and Western blot and in vitro for whole cell patch clamp recording and measurement of nitric oxide (NO) production by chemiluminescence.

RESULTS

Mycoplasma infection significantly inhibited AFC at 24 h and total and amiloride-sensitive AFC by 48 h postinfection (pi). In contrast, infected myeloperoxidase-deficient mice had similar basal and amiloride-sensitive AFC values to uninfected control mice at 48 h pi. Addition of forskolin restored total and amiloride-sensitive AFC to control values at 48 h pi. ATII cells isolated from infected mice demonstrated normal alpha, beta, and gamma ENaC total protein levels; however, infected whole-lung cell-surface levels of gamma ENaC were significantly decreased. Patch-clamp recordings demonstrated a significant decrease in total and amiloride-sensitive Na+ currents at 24 h pi. ATII cells demonstrated a significant increase in the production of NO at 24 h pi and inhibition of NO by ATII cells before infection reversed the decrease in total Na+ currents.

CONCLUSIONS

These data indicate that mycoplasma infection results in decreased AFC and functional ENaC via the production of reactive oxygen nitrogen intermediates.

Avoidance of the host immune system through phase variation in Mycoplasma pulmonis

Phase-variable lipoproteins are commonly found in Mycoplasma species. Mycoplasma pulmonis contains a family of extensively studied phase- and size-variable lipoproteins encoded by the vsa locus. The Vsa surface proteins vary at a high frequency, the in vivo significance of which has yet to be determined. We investigated the role of Vsa phase variation in respect to tissue tropism and avoidance of the immune system in the mouse host. Mycoplasmas were cultured 3, 14, and 21 days postinoculation from the nose, lung, trachea, liver, and spleen of experimentally infected C57BL/6 (wild-type), C57BL/6-RAG-1-/- (RAG-/-), and C57BL/6-inducible nitric oxide synthase (iNOS)-/- (iNOS-/-) mice. In wild-type and iNOS-/- mice, a large number of Vsa variants were seen by 21 days postinoculation. In contrast, little Vsa variation occurred in all tissues of RAG-/- mice. Analysis of isolates from 14 days postinoculation revealed less variation of the Vsa proteins in iNOS-/- mice than in the wild type. Western blot analysis of isolates from each strain of mouse demonstrated that Vsa phase variation occurred independently of size variation, indicating no obvious selection pressure for size variants. Additionally, these experiments provided no evidence that mycoplasmas producing particular Vsa proteins adhered only to specific tissues. The data strongly indicate that Vsa phase variation is a mechanism for avoidance of the immune system with no obvious contribution to tissue tropism.

Resistance of Mycoplasma pulmonis to complement lysis is dependent on the number of Vsa tandem repeats: shield hypothesis

The Vsa proteins are associated with the virulence of the murine respiratory pathogen Mycoplasma pulmonis. The antigens consist of a conserved N-terminal region that is combined with one of several different variable C-terminal regions comprised of tandem repeats. M. pulmonis strains that produce VsaA with about 40 tandem repeats do not adhere to polystyrene or erythrocytes and are highly resistant to complement killing. Strains that produce VsaA with three tandem repeats adhere strongly to polystyrene and erythrocytes and are highly susceptible to complement killing. We report here that the resistance to complement lysis was not due to a lack of activation of the complement cascade. Isolation and analysis of M. pulmonis strains that produced Vsa proteins other than VsaA (VsaG and VsaI) with either long or short repeat regions indicated that adherence to polystyrene and resistance to complement were dependent on the length of the repeat region but not on the Vsa type. Furthermore, M. pulmonis Vsa variants were susceptible to the polypeptide pore-forming molecule gramicidin D, independent of the Vsa type and length. Collectively, the data indicate the Vsa proteins nonspecifically mediate M. pulmonis surface interactions and function to sterically hinder access of complement to the mycoplasma cell membrane while permitting access of smaller molecules.

Role of surfactant protein-A in nitric oxide production and mycoplasma killing in congenic C57BL/6 mice

We generated congenic surfactant protein A (SP-A)-deficient (SP-A[-/-]) mice on the mycoplasma resistant C57BL/6 background (B6.SP-A[-/-]) and characterized their response to mycoplasma infection in comparison to C57BL/6 (B6) mice. B6.SP-A(-/-) mice infected with 10(6) colony-forming units (cfu) of Mycoplasma pulmonis had significantly higher bacterial lung loads than B6 mice at 72 h postinfection (p.i.). At the higher infection dose of 10(7), B6.SP-A(-/-) mice had significantly higher lung cfu at 24 h; however, no difference in mycoplasma cfu was observed between B6 and B6.SP-A(-/-) mice at 48 and 72 h p.i. We found that uninfected B6 mice had lower bronchoalveolar lavage nitrite (NO(2)(-)) and nitrate (NO(3)(-)) levels as compared with B6.SP-A(-/-) mice. On the other hand, infection of B6 mice with mycoplasmas resulted in significantly higher bronchoalveolar lavage NO(2)(-) and NO(3)(-) as compared with B6.SP-A(-/-) mice. These data indicate that SP-A may help regulate NO production in response to a specific stimulus, i.e., suppression of NO in the absence of bacteria and increased NO in the presence of bacteria. These data indicate that the contribution of SP-A to mycoplasma killing may be limited to lower doses of pathogens.

The Vsa proteins modulate susceptibility of Mycoplasma pulmonis to complement killing, hemadsorption, and adherence to polystyrene

The variable surface antigens (Vsa) of the murine respiratory pathogen Mycoplasma pulmonis are associated with the virulence of the microorganism in the lung. In strain UAB CT, the antigens consist of an N-terminal region that is combined with one of seven different C-terminal variable regions comprised of tandem repeats. M. pulmonis producing a VsaA protein with about 40 tandem repeats (R40) does not adhere to red blood cells or polystyrene. Strains that produce VsaH contain a short C-terminal region that lacks tandem repeats and adhere to red blood cells and plastic. We isolated and analyzed M. pulmonis strain CT variants (CT182 and derivatives) that produced a VsaA protein with only three tandem repeats (R3). These variants adhered to plastic and red blood cells similarly to the VsaH-producing strain. When the R3-producing CT182 strain or the VsaH-producing strains were incubated with normal guinea pig serum, they were efficiently killed. Killing was abolished when the serum was heat inactivated. In contrast, the M. pulmonis strains that produced VsaA R40 were highly resistant to complement killing. CT182R3 variants that survived the complement killing reactions all produced the R40 form of VsaA and were resistant to complement killing. VsaA R40 is the first mycoplasmal protein shown to be associated with resistance to complement. As both VsaH and VsaA can mediate adherence to plastic, cytadherence, and susceptibility to complement, we propose that Vsa modulates these phenotypes by nonspecific interactions.

Gene transfer in Mycoplasma pulmonis

Experiments were undertaken to examine gene transfer in Mycoplasma pulmonis. Parent strains containing transposon-based tetracycline and chloramphenicol resistance markers were combined to allow transfer of markers. Two mating protocols were developed. The first consisted of coincubating the strains in broth culture for extended periods of time. The second protocol consisted of a brief incubation of the combined strains in a 50% solution of polyethylene glycol. Using either protocol, progeny that had acquired antibiotic resistance markers from both parents were obtained. Analysis of the progeny indicated that only the transposon and not flanking genomic DNA was transferred to the recipient cell. Gene transfer was DNase resistant and probably the result of conjugation or cell fusion.

Gene rearrangements in the vsa locus of Mycoplasma pulmonis

The vsa genes of Mycoplasma pulmonis encode the V-1 lipoproteins. Most V-1 proteins contain repetitive domains and are thought to be involved in mycoplasma-host cell interactions. Previously, we have reported the isolation and characterization of six vsa genes comprising a 10-kb region of the genome of M. pulmonis strain KD735-15. In the current study, vsa-specific probes were used to clone several fragments from a genomic library of KD735-15 DNA and assemble a single 20-kb contig containing 11 vsa genes. The middle region of the vsa locus contains a large open reading frame (ORF) that is not a vsa gene and has undergone an internal deletion in some strains. The ORF is predicted to encode a membrane protein that may have a role in disease pathogenesis. To examine vsa genes in a strain of M. pulmonis that is unrelated to KD735-15, strain CT was studied. Through Southern hybridization and genomic cloning analyses, CT was found to possess homologs of the KD735-15 vsaA, -C, -E, and -F genes and two unique genes (vsaG and vsaH) that were not found in KD735-15. High-frequency, site-specific DNA inversions serve to regulate the phase-variable production of individual V-1 proteins. As a result of the sequence analysis of vsa recombination products, a model in which DNA inversion arises from strand exchange involving at least six nucleotides of the vrs box is proposed.

Upper respiratory tract disease in the gopher tortoise is caused by Mycoplasma agassizii

Upper respiratory tract disease (URTD) has been observed in a number of tortoise species, including the desert tortoise (Gopherus agassizii) and the gopher tortoise (Gopherus polyphemus). Clinical signs of URTD in gopher tortoises are similar to those in desert tortoises and include serous, mucoid, or purulent discharge from the nares, excessive tearing to purulent ocular discharge, conjunctivitis, and edema of the eyelids and ocular glands. The objectives of the present study were to determine if Mycoplasma agassizii was an etiologic agent of URTD in the gopher tortoise and to determine the clinical course of the experimental infection in a dose-response infection study. Tortoises were inoculated intranasally with 0.5 ml (0.25 ml/nostril) of either sterile SP4 broth (control group; n = 10) or 10(8) color-changing units (CCU) (total dose) of M. agassizii 723 (experimental infection group; n = 9). M. agassizii caused clinical signs compatible with those observed in tortoises with natural infections. Clinical signs of URTD were evident in seven of nine experimentally infected tortoises by 4 weeks postinfection (p.i.) and in eight of nine experimentally infected tortoises by 8 weeks p.i. In the dose-response experiments, tortoises were inoculated intranasally with a low (10(1) CCU; n = 6), medium (10(3) CCU; n = 6), or high (10(5) CCU; n = 5) dose of M. agassizii 723 or with sterile SP4 broth (n = 10). At all time points p.i. in both experiments, M. agassizii could be isolated from the nares of at least 50% of the tortoises. All of the experimentally infected tortoises seroconverted, and levels of antibody were statistically higher in infected animals than in control animals for all time points of >4 weeks p.i. (P < 0.0001). Control tortoises in both experiments did not show clinical signs, did not seroconvert, and did not have detectable M. agassizii by either culture or PCR at any point in the study. Histological lesions were compatible with those observed in tortoises with natural infections. The numbers of M. agassizii 723 did not influence the clinical expression of URTD or the antibody response, suggesting that the strain chosen for these studies was highly virulent. On the basis of the results of the transmission studies, we conclude that M. agassizii is an etiologic agent of URTD in the gopher tortoise.

Surfactant protein A mediates mycoplasmacidal activity of alveolar macrophages by production of peroxynitrite

We have previously shown that surfactant protein A (SP-A) mediates in vitro killing of mycoplasmas by alveolar macrophages (AMs) from resistant C57BL/6 mice through a nitric oxide (.NO)-dependent mechanism. Herein, SP-A-deficient [SP-A(-/-)] and inducible.NO synthase-deficient [iNOS(-/-)] mice were infected intranasally with 10(5) or 10(7) colony-forming units of Mycoplasma pulmonis. SP-A(-/-) mice were as susceptible to mycoplasmal infection as highly susceptible C3H/He mice, and far more susceptible than resistant C57BL/6 mice. iNOS(-/-) mice had significantly greater numbers of mycoplasmas and severity of lung lesions than iNOS(+/+) controls. In vitro, AMs isolated from C57BL/6 mice, activated with IFN-gamma, incubated with SP-A (25 micrograms/ml), and infected with 10(10) colony-forming units of M. pulmonis, killed mycoplasmas within 6 h. Mycoplasmal killing was abrogated by 1,000 units/ml of copper-zinc superoxide dismutase. In the absence of AMs, incubation of M. pulmonis with the peroxynitrite generator 3-morpholinosynodiomine.HCl (SIN-1) effected complete killing of mycoplasmas by 90 min in a dose-dependent manner. Addition of copper-zinc superoxide dismutase (3,000 units/ml), which converts SIN-1 to a.NO donor, prevented this killing. Neither of the reactive oxygen species generated by xanthine oxidase (10 milliunits/ml, plus 500 microM xanthine and 100 microM FeCl3), nor.NO generated by 1-propanamine-3-(2-hydroxy-2-nitroso-1-propylhydrazine (PAPA NONOate) (100 microM) killed mycoplasmas. These data establish that peroxynitrite generation by AMs is necessary for the killing of a pathogen in vitro and in vivo.

Roles of innate and adaptive immunity in respiratory mycoplasmosis

Current evidence suggests that host defense in respiratory mycoplasmosis is dependent on both innate and humoral immunity. To further delineate the roles of innate and adaptive immunity in antimycoplasmal defenses, we intranasally infected C3H/HeSnJ-scid/scid (C3H-SCID), C3H/HeSnJ (C3H), C57BL/6J-scid/scid (C57-SCID), and C57BL/6N (C57BL) mice with Mycoplasma pulmonis and at 14 and 21 days postinfection performed quantitative cultures of lungs and spleens, quantification of lung lesions, and histopathologic assessments of all other major organs. We found that numbers of mycoplasmas in lungs were associated with genetic background (C3H susceptible, C57BL resistant) rather than functional state of adaptive immunity, indicating that innate immunity is the main contributor to antimycoplasmal defense of the lungs. Extrapulmonary dissemination of mycoplasmas with colonization of spleens and histologic lesions in multiple organs was a common occurrence in all mice. The absence of adaptive immune responses in severe combined immunodeficient (SCID) mice resulted in increased mycoplasmal colonization of spleens and lesions in extrapulmonary sites, particularly spleens, hearts, and joints, and also reduced lung lesion severity. The transfer of anti-M. pulmonis serum to infected C3H-SCID mice prevented extrapulmonary infection and disease, while the severity of lung lesions was restored by transfer of naive spleen cells to infected C3H-SCID mice. Collectively, our results strongly support the conclusions that innate immunity provides antimycoplasmal defense of the lungs and humoral immunity has the major role in defense against systemic dissemination of mycoplasmal infection, but cellular immune responses may be important in exacerbation of mycoplasmal lung disease.

Surfactant protein A mediates mycoplasmacidal activity of alveolar macrophages

Mycoplasma pneumoniae is a leading cause of pneumonia and exacerbates other respiratory diseases in humans. We investigated the potential role of surfactant protein (SP) A in antimycoplasmal defense using alveolar macrophages (AMs) from C57BL/6NCr (C57BL) mice, which are highly resistant to infections of Mycoplasma pulmonis. C57BL AMs, activated with interferon (IFN)-gamma and incubated with SP-A (25 micrograms/ml) at 37 degrees C, produced significant amounts of nitric oxide (.NO; nitrate and nitrite production = 1.1 microM.h-1.10(5) AMs-1) and effected an 83% decrease in mycoplasma colony-forming units (CFUs) by 6 h postinfection. Preincubation of AMs with the inducible nitric oxide synthase inhibitor NG-monomethyl-L-arginine abolished .NO production and SP-A-mediated killing of mycoplasmas. No decrease in CFUs was seen when IFN-gamma-activated macrophages were infected with mycoplasmas in the absence of SP-A despite significant .NO production (nitrate and nitrite production = 0.6 microM.h-1.10(5) AMs-1). These results demonstrate that SP-A mediates killing of mycoplasmas by AMs, possibly through an .NO-dependent mechanism.

Pathogenicity of cilia-associated respiratory (CAR) bacillus isolates for F344, LEW, and SD rats

We conducted experiments to test whether rats of F344, LEW, and SD strains differ in susceptibility to mycoplasma-free isolates of cilia-associated respiratory (CAR) bacillus, whether Mycoplasma pulmonis can affect expression of CAR bacillus disease, and whether isolates of CAR bacillus differ in virulence for rats. In the first experiment, 24 rats of each strain were inoculated intranasally with 10(7) bacilli of CAR bacillus X1428D/AS, and 24 rats of each strain were inoculated with sterile medium (controls). Eight weeks later, eight inoculated rats and eight control rats of each strain were euthanatized, eight inoculated and eight control rats were given 10(6.5) colony-forming units of M. pulmonis X1428D, and eight inoculated rats and eight control rats were sham inoculated. Four rats of each group were euthanatized 4 or 8 weeks after the second inoculation. Severity of lesions in nasal passages, middle ear, trachea, and lungs was assessed by scoring. Rats of all three strains given CAR bacillus had typical lesions of similar severity; M. pulmonis X1428D was avirulent and did not exacerbate CAR bacillus disease. In the second experiment, groups of eight rats of F344 and SD strains were given 10(5) or 10(7) CAR bacillus X1328E, X1428D/AS, or X2450D and euthanatized 8 or 16 weeks later. Isolates X1428D/AS and X2450D caused similar lesions in rats of both strains and at both doses, but CAR bacillus X1328E was avirulent. Rats of the tested strains are similarly susceptible to CAR bacillus disease, but CAR bacillus isolates differ in virulence.

Depletion of alveolar macrophages exacerbates respiratory mycoplasmosis in mycoplasma-resistant C57BL mice but not mycoplasma-susceptible C3H mice

Indirect evidence suggests that innate immune mechanisms involving alveolar macrophages (AMs) are of major importance in antimycoplasmal defense. We compared the effects of AM depletion on intrapulmonary killing of Mycoplasma pulmonis during the early phase of infection in mycoplasma-resistant C57BL/6NCr (C57BL) and mycoplasma-susceptible C3H/HeNCr (C3H) mice. More than 80% of AMs were depleted in both strains of mice by intratracheal insufflation of liposome-encapsulated dichloromethylene bisphosphonate (L-Cl2MBP), compared to no significant AM depletion in either strain following insufflation of liposome-encapsulated phosphate-buffered saline (L-PBS), PBS alone, or no treatment. AM-depleted (L-Cl2MBP) and control (L-PBS) mice were infected intranasally with 10(5) CFU of M. pulmonis UAB CT, and their lungs were quantitatively cultured to assess intrapulmonary killing at 0, 8, 12, and 48 h postinfection. AM depletion exacerbated the infection in C57BL mice by reducing killing of the organism to a level comparable to that in C3H mice without AM depletion. In contrast, AM depletion did not alter killing in C3H mice. These results directly identify the AM as the main effector cell in early pulmonary antimycoplasmal defense and suggest that differences in mycoplasmal killing by AMs may explain the resistance of C57BL mice and the susceptibility of C3H mice to mycoplasmal infection.

Resistance to mycoplasmal lung disease in mice is a complex genetic trait

Mouse strains differ markedly in resistance to Mycoplasma pulmonis infection, and investigation of these differences holds much promise for understanding the mechanisms of antimycoplasmal host defenses. To determine the potential genetic diversity of resistance to disease in murine respiratory mycoplasmosis (MRM) and to select disease-resistant and nonresistant mouse strains for further genetic analysis, we screened 17 inbred mouse strains of various Bcg and H-2 genotypes for resistance to M. pulmonis. Mice were inoculated intranasally with 10(4) CFU of M. pulmonis UAB CT and evaluated at 21 days postinfection for severities of the four histologic lung lesions characteristic of MRM: alveolar exudate, airway exudate, airway epithelial hyperplasia, and lymphoid infiltrate. On the basis of these assessments of MRM severity, one group of mouse strains was found to be extremely resistant to disease (C57BR/cdJ, C57BL/6NCr, C57BL/10ScNCr, and C57BL/6J). The remaining strains of mice (C57L/J, SJL/NCr, BALB/cAnNCr, A/JCr, C3H/HeJ, SWR/J, AKR/NCr, CBA/NCr, C58/J, DBA/2NCr, C3H/HeNCr, C3HeB/FeJ, and C3H/HeJCr) developed disease of widely varying severities. Furthermore, strains in the group with more disease varied in pattern of lesion severity. While the severities of all four lesions were correlated in most mouse strains, this was not always true. DBA/2NCr mice had one of the highest scores for alveolar exudate, only a moderate score for airway exudate, and significantly lower scores for both airway epithelial hyperplasia and lymphoid infiltrate than all other strains susceptible to lung disease. DBA/2NCr mice had one of the highest mortality rates. We concluded that resistance to MRM is a complex trait. The observed differences in lung disease severity could not be explained by known differences at the Bcg or H-2 locus in the strains of mice we studied.

Sequence analysis of the chromosomal region around and within the V-1-encoding gene of Mycoplasma pulmonis: evidence for DNA inversion as a mechanism for V-1 variation

Although the variation of V-1 antigens of Mycoplasma pulmonis has been correlated with variable expression of the cytadherence properties of this organism and has been implicated as a virulence determining factor in M. pulmonis-induced murine respiratory disease, the precise function of these antigens remains unknown. We have cloned and characterized genes encoding V-1 from two M. pulmonis UAB CT V-1 variants that differ in hemadsorption properties. A comparison of the nucleotide sequences revealed that these two variant genes were identical in the 5'-most 724 nucleotides. Regions of extensive divergence that contained repeated sequences were found 3' to this conserved region. On the basis of their deduced amino acid sequences, one variant expressed a V-1 protein of 94.2 kDa presumptively containing 40 repeats of 17 amino acids and the other expressed a protein of 27.4 kDa consisting 2 direct, noncontiguous 9-amino-acid repeats. These general properties, as well as the presence of a prokaryotic lipoprotein acylation sequence (L-X-Y-C), indicated that the genes encoding V-1 were similar in structure to genes encoding other mycoplasma surface lipoproteins. Further analysis of sequences flanking these genes revealed that these variants arose via an inversion event which provided an interchange of the two variable regions as well as for the conserved region of these genes and immunoblot analyses using rabbit polyclonal antibodies specific for synthetic peptides derived from the sequences of the different variable regions indicated that DNA inversion acted as a switch which allowed only one of the two different genes to be expressed at any given time. This inversion model clearly provides a mechanism by which M. pulmonis can alter its surface architecture and also strongly suggests that the as-yet-undefined function of V-1 residues in the variable carboxy region of these proteins.

Gene expression and production of tumor necrosis factor alpha, interleukin 1, interleukin 6, and gamma interferon in C3H/HeN and C57BL/6N mice in acute Mycoplasma pulmonis disease

Studies were conducted to determine whether the production of various cytokines is associated with Mycoplasma pulmonis disease expression. Susceptible C3H/HeN and resistant C57BL/6N mice were inoculated intranasally with 10(7) CFU of virulent M. pulmonis UAB CT or avirulent M. pulmonis UAB T. Expression of genes for tumor necrosis factor alpha (TNF-alpha), interleukin 1 alpha (IL-1 alpha), IL-1 beta, IL-6, and gamma interferon (IFN-gamma) in whole lung tissue and TNF-alpha gene expression in bronchoalveolar lavage (BAL) cells was determined by reverse transcription-PCR using specific cytokine primers at various times postinoculation. In addition, concentrations of TNF-alpha, IL-1, IL-6, and IFN-gamma were determined in BAL fluid and serum samples at various times postinoculation. Our results showed that there was a sequential appearance of cytokines in the lungs of infected mice: TNF-alpha, produced primarily by BAL cells, appeared first, followed by IL-1 and IL-6, which were followed by IFN-gamma. Susceptible C3H/HeN mice had higher and more persistent concentrations of TNF-alpha and IL-6 in BAL fluid than did resistant C57BL/6N mice, indicating that TNF-alpha and possibly IL-6 are important factors in pathogenesis of acute M. pulmonis disease in mice. Serum concentrations of IL-6 were elevated in C3H/HeN mice, but not C57BL/6N mice, following infection with M. pulmonis, suggesting that IL-6 has both local and systemic effects in M. pulmonis disease.

Chronic respiratory mycoplasmosis in C3H/HeN and C57BL/6N mice: lesion severity and antibody response

Mycoplasma pneumoniae is a leading, worldwide cause of death and disability due to pneumonia. Mycoplasma pulmonis infection in mice is an invaluable model for the study of host defenses against respiratory mycoplasmas in vivo. C3H/HeN mice are much more susceptible to acute inflammatory lung disease due to M. pulmonis than C57BL/6N mice, but little is known about the chronic disease in these mouse strains. We infected C3H/HeN and C57BL/6N mice with 10(4) CFU of M. pulmonis UAB CT and evaluated them at weekly intervals by quantitative mycoplasma culture of nasal passages, trachea, and lungs, assessment of lesion severity in nasal passages, trachea, and lungs, and determination of serum immunoglobulin classes and subclasses by enzyme-linked immunosorbent assay. We found that C3H/HeN mice had 2 to 5 logs more organisms in their lungs and far more severe lung disease than C57BL/6N mice through 63 days postinfection. Although both strains of mice developed the same classes of antibody, C3H/HeN mice had much greater anti-M. pulmonis immunoglobulin G (IgG) responses in the IgG1 and IgG2a subclasses than C57BL/6N mice. These results suggest that adaptive immunity does not effect resolution of chronic mycoplasma infection and disease in the lungs.

Effects of aging on antibody avidity to Mycoplasma pulmonis

Antibody avidity of serum and lung lavage responses was examined in rats to determine aging effects on functional differences in antibody to Mycoplasma pulmonis. Three age groups of animals (weanling, adult and senescent) were immunized with either of two doses of formalinized M. pulmonis as the antigen, or a placebo control. Total immunoglobulin levels and specific antibody responses were examined in serum and lung lavage fluids and subsequently avidity measurements of the same samples were made for the specific antibody to M. pulmonis. The concentration of NH4SCN that dissociated 50% of the antibody was used to determine the avidity index of the serum and lung lavage samples. Total serum IgG and IgA were decreased in the weanling animals when compared to the other two age groups of animals. In contrast, serum IgA levels were substantially increased in senescent animals. Significant increases in serum IgA levels were noted following immunization that was not observed for IgG levels. Substantial increases in both serum antibody and lung lavage antibody were observed in response to immunization with either dose of antigen, but only the lung lavage samples showed both IgG and IgA isotypes differences that were attributable to age. Serum IgG avidity indices gradually increased over time following immunization with higher indices being observed in the weanling animals immunized with the higher M. pulmonis dose. Serum IgA avidity indices also increased over time with no significant differences noted among the age groups. Lung lavage IgG avidity demonstrated slightly higher indices in the weanling animals, while lung lavage IgA avidity showed higher avidity indices in the senescent animals at the higher antigen dose. These data suggest that senescent animals are capable of producing an apparently functional antibody response and that differences noted in increased disease susceptibility in older animals may be attributed to mechanisms other than a dysfunctional humoral immune response at mucosal surfaces.

Comparison of a lesion-inducing isolate and a non-lesional isolate of Candida albicans in an immunosuppressed rat model of oral candidiasis

Two distinct strain-related patterns of organism-host interaction on dorsal tongue of immunocompetent rats have been identified for Candida albicans: some isolates induce mucosal lesions, while other isolates penetrate the keratin layer but do not produce a lesion. This study examined the behavior of each of the two types of isolates in a cyclosporin-immunosuppressed rat model. Groups B (normal) and D (cyclosporin) were orally inoculated with a lesion-inducing isolate of C. albicans, while a non-lesional isolate was given to Groups A (normal) and C (cyclosporin). A typical dorsal tongue lesion developed in 4/18 rats in Group B and in 13/16 in Group D (P = 0.00267). No significant difference in infection rate between the normal and cyclosporin-treated animals was seen for the non-lesional isolate. The lack of a host inflammatory response associated with the non-lesional isolate may represent an ecologic advantage for the organism.

Membrane-associated nuclease activities in mycoplasmas

Membrane-associated nucleases of various mycoplasmal species were investigated by using two nuclease assays. A lambda DNA assay was developed to measure nuclease activity associated with whole-cell suspensions, activity released from intact cells, and activity associated with detergent-disrupted cells. In most species, nuclease activities were entirely membrane associated, and disruption by a detergent had a stimulatory effect on these activities. All mycoplasmal species contained nuclease activity, but Mycoplasma capricolum was unusual because its activity was dependent upon magnesium and was inhibited by calcium. We developed a sodium dodecyl sulfate-polyacrylamide gel electrophoresis system that produced reproducible nuclease patterns, and this system was used to determine the apparent molecular weights of the nuclease proteins. An examination of 20 mycoplasmal species failed to identify common bands in their nuclease patterns. An examination of 11 Mycoplasma pulmonis strains, however, indicated that nuclease patterns on polyacrylamide gels may provide a means for categorizing strains within a species. Our results suggest that nucleases are important constituents of mycoplasmal membranes and may be involved in the acquisition of host nucleic acids required for growth.

Cultivation of cilia-associated respiratory bacillus in artificial medium and determination of the 16S rRNA gene sequence

Cilia-associated respiratory (CAR) bacillus, an unclassified gliding bacterium associated with respiratory disease in rats, mice, and rabbits, has previously been cultivated only in embryonated chicken eggs, cell culture, or cell culture medium supplemented with conditioned medium from cultured tracheas. A reference strain of CAR bacillus, originally isolated in eggs, grew in cell culture flasks as adherent individual bacilli and ropy, whorled fascicles in cell culture media supplemented only with fetal calf serum. Using Dulbecco's minimal essential medium, we isolated CAR bacillus from naturally infected rats and a naturally infected rabbit and from experimentally inoculated mice and rats. Isolates were maintained for up to 20 passages. Isolates from rats were similar in morphology to the reference strain, but most were more actively motile and formed pincushion-like aggregates. The rabbit bacilli were smaller and formed fewer aggregates. DNAs of rat isolates differed only slightly in restriction fragment patterns from that of the reference strain, whereas that of the rabbit isolate was distinctly different. Cultures of CAR bacilli of all strains from rats contained Mycoplasma fermentans, Mycoplasma pulmonis, or both, and cultures of the CAR bacillus from the rabbit contained an unidentified arginine-utilizing mycoplasma. The sequence of the 16S rRNA gene of the reference strain was determined by amplification by polymerase chain reaction, cloning of the product, and sequencing by the dideoxynucleotide chain termination method. Comparison of the sequence with sequences in the GenBank data base indicated that CAR bacillus is a unique organism most closely related to Flavobacterium ferrugineum and Flexibacter sancti.

Identification and characterization of IS1138, a transposable element from Mycoplasma pulmonis that belongs to the IS3 family

Insertion sequence (IS) elements are mobile genetic elements found in prokaryotes. We have identified a repetitive element from Mycoplasma pulmonis, a murine pathogen, that is similar to eubacterial IS elements. By subcloning a single strain of M. pulmonis, we isolated a variant clone in which the IS element had undergone an apparent transposition event. The nucleotide sequences of the element, designated IS1138, and the target site into which it inserted were determined. IS1138 consists of 1288 bp with 18 bp perfect terminal inverted repeats. Sequence analysis of the target site before and after insertion of IS1138 identified a 3 bp duplication of target DNA flanking the element. The predicted amino acids encoded by the major open reading frame of IS1138 share significant similarity with the transposases of the IS3 family. Southern hybridization analysis indicates that repetitive sequences similar to IS1138 are present in most, if not all, strains of M. pulmonis, but IS1138-like sequences were not detected in other mycoplasmal species.

Effects of aging on exocrine immune responses to Mycoplasma pulmonis

Formalinized Mycoplasma pulmonis was used to immunize 3 different age groups of Fischer 344 rats. A specific antibody to this antigen was detected in both saliva and lung lavage fluids and differences were noted in the elicitation of secretory antibody between the different ages of the animals. Few statistical differences were noted between the three age groups for salivary IgG responses to M. pulmonis, regardless of the dosage given, even though all responses were greater than their respective control groups. The principal differences among the three age groups were noted in the kinetics of the response, that is, the amount of time that was necessary to produce a peak response. The younger group of animals took less time to produce a peak response than the older two groups, even though the magnitude of the response was lower. Salivary IgA responses to M. pulmonis appeared predominantly as a primary response, particularly in the senescent animals. Secondary salivary IgA responses were not significantly greater than their respective primary responses, suggesting that secretory IgA did not display classic anamnestic responses that were observed with salivary IgG. As with IgG responses, the senescent animals took longer to produce a peak salivary IgA response when compared to the other age groups. Lung lavage IgG responses, normalized to total protein, were greatest in the youngest group of animals and appeared to diminish as the age of the animal increased. In contrast, lung lavage IgA responses to M. pulmonis were of a greater magnitude in the senescent animals. These studies suggest that senescent animals are capable of eliciting a humoral immune response in mucosal secretions to Mycoplasma pulmonis. However, differences noted with regard to disease severity and mortality to respiratory mycoplasmosis in senescent animals may result from intrinsic defects in the quality of the humoral response or as a consequence of deficient cellular responses to this pathogen.

Secretory immune responses to Mycoplasma pulmonis

Formalinized Mycoplasma pulmonis, along with aluminum hydroxide as an adjuvant, was used to subcutaneously immunize rats in the vicinity of the salivary gland to examine the characteristics of the secretory immune response to this pathogen. The induction of specific antibody to this microorganism was detected in serum and the exocrine fluids, namely, saliva and lung lavage fluid. Both immunoglobulin G (IgG) and IgA isotype antibodies were detected in each of these fluids after primary and secondary local immunizations. Serum responses from immunized animals were significantly greater than in the control group, but a dose response was not observed in either IgG or IgA antibody at the dosages selected for immunization. Salivary IgG antibody responses peaked early after both the primary and secondary immunizations, exhibiting a clear dose response. Salivary IgA in immunized groups was significantly greater than that in the control group but displayed little dose-dependent kinetics, and, at the termination of the experiment, this response had not yet peaked. Lung lavage IgG and IgA were minimal after the primary immunization when the antibody was normalized to total protein but displayed dose-dependent kinetics after a secondary challenge. IgG peaked immediately after a secondary challenge, while IgA peak responses were observed only after 20 days. A positive correlation was noted between the serum, saliva, and lung lavage fluid IgGs after both primary and secondary immunizations and only after a secondary challenge for IgA. In this study we were able to elicit a secretory immune response, consisting of both IgG and IgA, which exhibited a dose-dependent characteristic in lung lavage fluid to this immunogen. Additionally, a positive correlation of antibody levels between saliva and lung lavage fluid suggests that saliva could be used as an indicator for monitoring specific antibody to M. pulmonis in lung lavage secretions without requiring invasive, deleterious procedures.

Mycoplasma pulmonis infections cause long-lasting potentiation of neurogenic inflammation in the respiratory tract of the rat

These experiments were done to learn whether Mycoplasma pulmonis infections of the respiratory tract of rats can potentiate "neurogenic inflammation" and whether this potentiation is amplified by factors that exacerbate the infections. Pathogen-free F344 rats were inoculated intranasally with M. pulmonis or with sterile culture medium and then lived for 4 wk in an ammonia-free atmosphere or in air containing ammonia (100 parts per million). Neurogenic inflammation was evoked by an intravenous injection of capsaicin, and 5 min later the magnitude of the response was quantified by measuring the amount of extravasation of two tracers, Monastral blue pigment and Evans blue dye. We found that vascular permeability in the tracheas of all rats was normal in the absence of capsaicin. However, a 75-micrograms/kg dose of capsaicin, which caused almost no extravasation of Evans blue in the tracheas of pathogen-free controls (17 +/- 3 ng/mg; mean +/- SE), produced extensive extravasation in the infected rats (135 +/- 18 ng/mg; P less than 0.001). Similarly, this dose of capsaicin produced 30 times as much Monastral blue extravasation in the infected rats (area density = 47 +/- 8% of surface area) as it did in the pathogen-free rats (1.6 +/- 0.5%; P less than 0.001), a difference that resulted from increases in the number of Monastral blue-labeled postcapillary venules and in the amount of labeling per venule. Exposure of the infected rats to ammonia exacerbated the infections, further increased the number of Monastral blue-labeled vessels and the amount of labeling per vessel, and made the rats so sensitive to capsaicin that a normally tolerable dose of 150 micrograms/kg i.v. caused fatal apnea. Ammonia did not have these effects in pathogen-free rats. We conclude that M. pulmonis infections of the airway mucosa cause a potent, long-lasting potentiation of neurogenic inflammation, which results in part from an increase in the number and responsiveness of mediator-sensitive postcapillary venules. These changes can be amplified by environmental factors such as ammonia which exacerbate the infections.

Clearance of different strains of Mycoplasma pulmonis from the respiratory tract of C3H/HeN mice

Pathogen-free C3H/HeN mice were exposed by aerosol to Mycoplasma pulmonis PG34(ASH), UAB 5782C, M1, UAB T, or UAB CT, and clearance of mycoplasmas from the nasal passages, trachea, and lungs was determined during the first 72 h postinoculation (PI). There were differences among strains of mycoplasmas in physical removal of organisms and in killing by nonspecific factors in the nasal passages and trachea. The avirulent strain, PG34(ASH), was quickly removed from the nasal passages and trachea. Physical removal of the other mycoplasmal strains occurred slowly, with 60 to 89% of the radioactive label remaining in the nasal passages and trachea even after 72 h. There were significant differences in killing among mycoplasmal strains by nonspecific host mechanisms in the nasal passages, trachea, and lungs. Strain UAB T was quickly killed at all levels of the respiratory tract. Strains UAB 5782C and M1 were killed at all three sites by 2 to 4 h PI. The most virulent strain, UAB CT, was killed much more slowly than the other strains. However, there was no statistical difference in the relative numbers of mycoplasmas present in the lungs at 72 h PI among strains UAB CT, UAB 5782C, and M1. These studies showed that the different mycoplasmal strains were cleared from the respiratory tract by different mechanisms and suggest that the differences in virulence among the mycoplasma strains can be explained, in part, by the differences in elimination of the organisms from the respiratory tract by nonspecific host defense mechanisms.

Colony opacity, hemadsorption, hemolysis, and mitogenicity are not associated with virulence of Mycoplasma pulmonis

Colony opacity, hemadsorption and hemolysis of erythrocytes, and the ability of whole mycoplasmal cells to induce a blastogenic response when incubated with C3H/HeN or C57BL/6 mouse lymphocytes were examined for 18 strains of Mycoplasma pulmonis to determine if any of these characteristics could be associated with virulence in vivo. Although there were differences among strains in each of these characteristics, none of these parameters were associated with virulence.