Serum antibody does not account for differences in the severity of chronic respiratory disease caused by Mycoplasma pulmonis in LEW and F344 rats

THE MULTIFACETED ROLE OF T CELL-MEDIATED IMMUNITY IN PATHOGENESIS AND RESISTANCE TO MYCOPLASMA RESPIRATORY DISEASE

Mycoplasma respiratory diseases have a significant impact on the economy, health and wildlife. The hallmark of these diseases is the persistence of the mycoplasma infections and chronic inflammatory responses associated with the airways. There is still much that needs to be understood about the immune mechanisms involved in mycoplasma disease and resistance from infection. It is clear that immune responses can contribute to the generation of inflammatory lesions in mycoplasma respiratory disease, as well as provide protection from infection and extrapulmonary dissemination of the organisms. The evolution of this lung disease is under the control innate immune mechanisms and the contrasting effects of different T cell populations. The mechanisms of immunity involved in mycoplasma diseases are multifaceted, and a fascinating story of its complexity is being uncovered. Research in mycoplasma respiratory diseases have underscored the idea that immunity along the respiratory tract against infectious agents is a dynamic process and involves a network of cellular and cytokine signals that determine the type of responses generated, and ultimately, the outcome of infection. The aim of this article is to present on overview of our work on mycoplasma disease and immunity, focusing on the interactions and regulation of T cell responses that influence disease pathogenesis. We will first provide an overview of immune mechanisms involved in controlling infection and participate in the generation of T cell responses, and the role of T cell populations in generating protection and contributing to lesion development will be discussed.

Depletion of CD8+ T cells exacerbates CD4+ Th cell-associated inflammatory lesions during murine mycoplasma respiratory disease

Mycoplasma infection is a leading cause of pneumonia worldwide and can lead to other respiratory complications. A component of mycoplasma respiratory diseases is immunopathologic, suggesting that lymphocyte activation is a key event in the progression of these chronic inflammatory diseases. The present study delineates the changes in T cell populations and their activation after mycoplasma infection and determines their association with the pathogenesis of murine Mycoplasma respiratory disease, due to Mycoplasma pulmonis infection. Increases in T cell population numbers in lungs and lower respiratory lymph nodes were associated with the development of mycoplasma respiratory disease. Although both pulmonary Th and CD8(+) T cells increased after mycoplasma infection, there was a preferential expansion of Th cells. Mycoplasma-specific Th2 responses were dominant in lower respiratory lymph nodes, while Th1 responses predominated in spleen. However, both mycoplasma-specific Th1 and Th2 cytokine (IL-4 and IFN-gamma) responses were present in the lungs, with Th1 cell activation as a major component of the pulmonary Th cell response. Although a smaller component of the T cell response, mycoplasma-specific CD8(+) T cells were also a significant component of pulmonary lymphoid responses. In vivo depletion of CD8(+) T cells resulted in dramatically more severe pulmonary disease, while depletion of CD4(+) T cells reduced its severity, but there was no change in mycoplasma numbers in lungs after cell depletion. Thus, mycoplasma-specific Th1 and CD8(+) T cell activation in the lung plays a critical regulatory role in development of immunopathologic reactions in Mycoplasma respiratory disease.

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.

Serum and mucosal antibody responses and protection in pigs vaccinated against Mycoplasma hyopneumoniae with vaccines containing a denatured membrane antigen pool and adjuvant

OBJECTIVE

To investigate the protective efficacy of a pool of denatured membrane protein antigens of Mycoplasma hyopneumoniae (J strain) in the molecular size range 70 to 85 kDa (F3 antigen) in combination with adjuvants for pigs challenged with M hyopneumoniae.

DESIGN

A vaccine efficacy experiment with assessment of serum and respiratory tract antibody responses.

PROCEDURE

F3 antigens were emulsified with five different adjuvants. To groups of three pigs per vaccine, four vaccines were given by intramuscular injection, and two vaccines, including one of those given intramuscularly, were given by intraperitoneal injection.

RESULTS

Compared to six unvaccinated pigs, animals vaccinated with F3 antigen displayed significantly reduced pneumonia (54% reduction in mean lung score) following experimental challenge. Analysis of post-vaccination, pre-challenge IgG and IgA ELISA antibody absorbances in serum and respiratory tract washings revealed no correlation with lung score. Six weeks after challenge, pigs previously vaccinated intramuscularly mostly demonstrated greater IgG and IgA responses in respiratory tract washings, and greater IgG serum antibody responses, than those vaccinated by intraperitoneal injection.

CONCLUSION

Pigs vaccinated with M hyponeumoniae antigens in the molecular size range of 70 to 85 kDa showed a significant reduction in lung lesions compared with unvaccinated control animals after experimental challenge. IgG and IgA antibody concentrations in serum and respiratory tract washings after vaccination do not provide a useful prognostic indicator of protection from enzootic pneumonia.

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.

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.

Monoclonal antibodies that inhibit mitogenic activity of Mycoplasma pulmonis

Previous studies have suggested a correlation between mitogenic, polyclonal activation of host lymphocytes and the respiratory tract inflammatory diseases induced by Mycoplasma pulmonis. This study describes the generation of monoclonal antibodies (MAbs) to M. pulmonis membrane antigens with different capacities to inhibit stimulation of cultured rat lymphocytes by mycoplasmal membranes and with variable effects on M. pulmonis growth. We show that the inhibitory effects exerted on mitogenesis by purified MAbs are inversely related to the effects of MAbs on M. pulmonis growth. Immunoblotting of electrophoretically separated membrane proteins, with both growth- and mitogenesis-inhibiting antibodies, revealed significant changes in the reactions obtained with both types of MAb following short exposure of membranes to heat. Growth-inhibiting MAbs strongly react with heat-labile antigenic complexes with molecular weights of 65,000 to 75,000. Inhibition of mitogenesis is mainly associated with recognition of membrane complexes of 84 to 113 kDa that exhibit disperse smears and variable heat sensitivities. Following brief heating of membranes, more distinct bands of 103, 90, and 84 kDa are obtained with MAbs that inhibit mitogenesis. Experiments with other mitogenic mycoplasma species and MAb 3.3.10.2, a potent inhibitor of mitogenesis reveal that whereas the antigenic epitope recognized by this antibody is present on unheated membranes from different mycoplasmas, with heated membranes the MAb yields reactions only with M. pulmonis and M. arthritidis. Our studies suggest that M. pulmonis mitogens are unique membrane complexes of variable molecular weights, highly susceptible to heat and less sensitive to reducing agents.

Impact of experimental genital mycoplasmosis on pregnancy outcome in Sprague-Dawley rats

Specific-pathogen-free (SPF) female Sprague-Dawley rats were infected by intravaginal inoculation with 3 x 10(7) CFU of Mycoplasma pulmonis X1048 in 0.1 ml of Frey's broth or with an equal volume of sterile Frey's broth. A minimum of 10 days postinfection, rats were bred to noninfected males. Rats were necropsied at days 11, 14, and 18 of gestation and within 24 h of parturition. Throughout pregnancy, at least 50% of rats remained infected in the lower genital tract. At parturition, the major site of colonization was the respiratory tract (P = 0.02). M. pulmonis was not isolated from any site of any control rat. Pregnancy outcome was adversely affected by infection with M. pulmonis. Infected rats had significantly smaller litter sizes at day 18 of gestation (P < or = 0.01) and at term (P < or = 0.004). No statistically significant differences among the gestational stages in infected rats were noted for litter size. Total litter weight is a reflection of individual pup weight and of the number of pups born. Therefore, it was obvious that infected rats would have a significantly lower (P < or = 0.008) total litter weight than noninfected controls. However, when individual pup weights were considered, infected pups (n = 49) also had significantly lower (P < or = 0.0001) birth weights than did noninfected controls (n = 68). The incidence of an adverse pregnancy outcome at term (stillbirths, macerated fetuses, or resorptions) was higher (P < or = 0.01) in infected rats than in noninfected control rats. No stillborn pups or macerated fetuses were observed in any control term rats (n = 5). All control rats had live-born pups. Three infected rats had no live-born offspring. Resorptions were more common in infected rats than in control rats (P < or = 0.01). The mean number of resorptions per rat was greater in rats which went to term than in rats necropsied during gestation, indicating that the severity of disease was progressive. The rat is frequently the laboratory animal of choice for a wide variety of reproductive studies, and the experimental parameters that are most often measured (litter size, pup weight, and neonatal survival) were all adversely affected by genital mycoplasmosis. Genital mycoplasmosis is important as an animal model for the interaction of infectious agents and the host during pregnancy as well as in its own right as a confounding variable affecting research projects which use the rat as a model to study reproductive function and physiology.

Linkage map of seven polymorphic markers on rat chromosome 18

A genetic linkage map of seven polymorphic markers was created with F2 intercross progeny of F344/N and LEW/N rats and assigned to rat Chromosome (Chr) 18. Five of the markers described were defined by simple sequence length polymorphisms (SSLPs) associated with five genes: transthyretin (TTR), trypsin inhibitor-like protein (TILP), beta 2 adrenergic receptor (ADRB2), olfactory neuron-specific G protein (OLF), and gap junction protein (GJA1). One marker was defined by a restriction fragment length polymorphism (RFLP) detected with a probe for the human colony stimulating factor 1 receptor (CSF1R) gene. The D18N1R locus was defined by an anonymous DNA fragment amplified by the randomly amplified polymorphic DNA (RAPD) technique with a single short primer. These seven DNA loci formed a single genetic linkage group 30.4 cM in length with the following order: TTR-6.8 cM-D18N1R-9.1 cM-TILP-4.3 cM-CSF1R-0 cM-ADRB2-10.2 cM-OLF-0 cM-GJA1. The five SSLP markers were highly polymorphic. In a total of 13 inbred rat strains analyzed (F344/N, LEW/N, LOU/MN, WBB1/N, WBB2/N, MR/N, MNR/N, ACI/N, SHR/N, WKY/N, BN/SsN, BUF/N, and LER/N), three to six alleles were detected for each marker. Remarkable linkage conservation was detected between the region of rat Chr 18 mapped and a region of mouse Chr 18. However, genes associated with these markers have been mapped to three different human chromosomes (Chrs 5, 6, and 18). The markers described here should be useful for genetic mapping studies and genetic monitoring of inbred rat strains.

Map of seven polymorphic markers on rat chromosome 14: linkage conservation with human chromosome 4

Seven polymorphic markers identified by polymerase chain reaction (PCR) amplification, including markers for six genes--DRD1L (dopamine receptor, D1-like-2), GLUKA (glucokinase), PF4 (platelet factor 4), ALB (albumin), AFP (alpha-fetoprotein), and BSP (bone sialoprotein)--and one anonymous locus (D14N52), were mapped to a single 67-cM linkage group with F2 intercross progeny of F344/N and LEW/N inbred rat strains. Two of these markers, ALB and AFP, have previously been assigned to rat Chromosome (Chr) 14, allowing assignment of this entire linkage group. Five of the markers--DRD1L, PF4, ALB, AFP, and BSP--have been physically mapped to a large region of human Chr 4 encompassing the p arm and the q arm to band q28. Homologs of two of the markers, ALB and AFP, have been mapped to Chr 5 in the mouse. Comparison of human Chr 4 with the homologous regions on Chr 14 of the rat and Chr 5 of the mouse indicated that linkage conservation with human Chr 4 extends over a greater region in the rat than in the mouse. The markers described here were found to be highly polymorphic in twelve inbred strains (F344/N, LEW/N, ACI/N, BUF/N, BN/SsN, LOU/MN, MNR/N, MR/N, SHR/N, WBB1/N, WBB2/N, and WKY/N). These polymorphic markers should be useful in genetic linkage studies of important phenotypes in rats.

Infection-induced airway fibrosis in two rat strains with differential susceptibility

Chronic infections play a significant role in the morbidity and mortality of patients with chronic airflow limitation. By stimulating airway inflammation, persistent infection has the potential to cause airway fibrosis. However, in patient this condition is most typically found in lungs damaged by other factors, such as smoking, abnormal secretions, or barotrauma. We report the characterization of Mycoplasma pulmonis infection-induced lung fibrosis in two immunocompetent rat strains with no preexisting lung disease. The fibrosis was predominantly in the airways, as demonstrated by the findings for infected animals of increased airway inflammation, airway fibrosis, and airway wall thickness, which correlated with the collagen content of the lungs. Also, the physiological alterations were the opposite of those found in interstitial fibrosis, with a positive correlation between lung compliance and collagen content. The airway fibrosis was noted earlier and to a greater extent in Lewis rats than in Fisher rats, and this result apparently was related to regulation of the inflammatory response. Airway wall thickness, airway inflammation, and airway fibrosis are commonly reported in tissue specimens from patients with chronic airway diseases and have been shown to correlate with airflow limitation in patients with chronic obstructive pulmonary disease. Thus, this model may be useful in furthering our understanding of the role of chronic infection and airway inflammation in airflow obstruction.

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.

Specific and nonspecific antibody responses in different segments of the respiratory tract in rats infected with Mycoplasma pulmonis

Murine respiratory mycoplasmosis resulting from Mycoplasma pulmonis infection in rats provides a useful model for the study of immunological and inflammatory mechanisms operative in the respiratory tract. We have previously shown that LEW rats develop more severe disease than do F344 rats. To further study the production of antibody responses in chronic respiratory disease due to M. pulmonis infection, we examined the distribution and development of M. pulmonis-specific antibody-forming cells (AFC) in different segments of the respiratory tracts of infected LEW and F344 rats. In these studies, the upper respiratory nodes were the initial site of antibody production after infection and remained the major site for recovery of AFC. Since infected LEW rats had equal or higher numbers of AFC than did infected F344 rats, these results suggest that the level of local antibody production alone is not responsible for the decreased susceptibility of F344 rats to murine respiratory mycoplasmosis. The differences in total antibody responses appear to be due to the greater numbers of cells recovered from the tissues of infected LEW rats compared with those recovered from F344 rats, suggesting that LEW rats may have greater production of chemotactic factors. Also, we demonstrate that nonspecific activation and/or recruitment of B cells occurs in the respiratory tracts of both LEW and F344 rats after infection with M. pulmonis.

Immunoglobulin class- and subclass-specific responses to Mycoplasma pulmonis in sera and secretions of naturally infected Sprague-Dawley female rats

Mycoplasma pulmonis causes chronic murine respiratory mycoplasmosis and genital disease in rats. Specific immunoglobulin M (IgM), IgA, and IgG and its subclasses present in sera and tracheal and uterine lavage samples from 36 naturally infected Sprague-Dawley female rats were tested for reactivity with M. pulmonis in an enzyme-linked immunosorbent assay. Ten specific-pathogen-free Sprague-Dawley female rats served as the negative controls. Tracheal and uterine lavage samples were cultured quantitatively for M. pulmonis. M. pulmonis was isolated from the trachea (35 of 36) and uterus (17 of 36) of naturally infected rats; all rats were infected in at least one of the two sites cultured. M. pulmonis was not isolated from any control rat. There was a significant difference in levels of specific antibody of all classes except IgG2c between control and naturally infected animals (P less than 0.001 for IgM, IgG, IgG1, and IgG2a; P less than 0.002 for IgG2b; and P less than 0.02 for IgA). There was no correlation between numbers of M. pulmonis cells isolated and the amount or class of antibody measured in serum or tracheal lavage specimens. The predominant antibodies to M. pulmonis found in the sera of naturally infected rats were IgG and IgM. The IgG2a subclass was responsible for the majority of IgG-positive animals. There were no differences between rats which were positive by culture for M. pulmonis in the uterus (U+) and rats which were negative by culture for M. pulmonis in the uterus (U-) with respect to distribution or amount of antibody classes and subclasses in the serum. However, tracheal wash samples from U+ rats had significantly higher (P less than 0.03) levels of specific IgG1 and IgG2a than those from U- rats. Conversely, IgG2a was present in higher levels in pooled uterine lavage specimens from U- rats than in those from U+ rats.