Characterization of gamma interferon-mediated cytotoxicity to chlamydia-infected fibroblasts

Refinement of water-filtered infrared A (wIRA) irradiations of in vitro acute and persistent chlamydial infections

Water-filtered infrared A (wIRA) alone or in combination with visible light (VIS) exerts anti-chlamydial effects in vitro and in vivo in acute infection models. However, it has remained unclear whether reduced irradiation duration and irradiance would still maintain anti-chlamydial efficacy. Furthermore, efficacy of this non-chemical treatment option against persistent (chronic) chlamydial infections has not been investigated to date. To address this knowledge gap, we evaluated 1) irradiation durations of 5, 15 or 30 min in genital and ocular Chlamydia trachomatis acute infection models, 2) irradiances of 100, 150 or 200 mW/cm² in the acute genital infection model and 3) anti-chlamydial activity of wIRA and VIS against C. trachomatis serovar B and E with amoxicillin (AMX)- or interferon γ (IFN-γ)-induced persistence. Reduction of irradiation duration reduced anti-chlamydial efficacy. Irradiances of 150 to 200 mW/cm², but not 100 mW/cm², induced anti-chlamydial effects. For persistent infections, wIRA and VIS irradiation showed robust anti-chlamydial activity independent of the infection status (persistent or recovering), persistence inducer (AMX or IFN-γ) or chlamydial strain (serovar B or E). This study clarifies the requirement of 30 min irradiation duration and 150 mW/cm² irradiance to induce significant anti-chlamydial effects in vitro, supports the use of irradiation in the wIRA and VIS spectrum as a promising non-chemical treatment for chlamydial infections and provides important information for follow-up in vivo studies. Notably, wIRA and VIS exert anti-chlamydial effects on persistent chlamydiae which are known to be refractory to antibiotic treatment.

Toll-like receptor-2, but not Toll-like receptor-4, is essential for development of oviduct pathology in chlamydial genital tract infection

The roles of Toll-like receptor (TLR) 2 and TLR4 in the host inflammatory response to infection caused by Chlamydia trachomatis have not been elucidated. We examined production of TNF-alpha and IL-6 in wild-type TLR2 knockout (KO), and TLR4 KO murine peritoneal macrophages infected with the mouse pneumonitis strain of C. trachomatis. Furthermore, we compared the outcomes of genital tract infection in control, TLR2 KO, and TLR4 KO mice. Macrophages lacking TLR2 produced significantly less TNF-alpha and IL6 in response to active infection. In contrast, macrophages from TLR4 KO mice consistently produced higher TNF-alpha and IL-6 responses than those from normal mice on in vitro infection. Infected TLR2-deficient fibroblasts had less mRNA for IL-1, IL-6, and macrophage-inflammatory protein-2, but TLR4-deficient cells had increased mRNA levels for these cytokines compared with controls, suggesting that ligation of TLR4 by whole chlamydiae may down-modulate signaling by other TLRs. In TLR2 KO mice, although the course of genital tract infection was not different from that of controls, significantly lower levels of TNF-alpha and macrophage-inflammatory protein-2 were detected in genital tract secretions during the first week of infection, and there was a significant reduction in oviduct and mesosalpinx pathology at late time points. TLR4 KO mice responded to in vivo infection similarly to wild-type controls and developed similar pathology. TLR2 is an important mediator in the innate immune response to C. trachomatis infection and appears to play a role in both early production of inflammatory mediators and development of chronic inflammatory pathology.

Gamma interferon and interleukin-10 gene expression in synovial tissues from patients with early stages of Chlamydia-associated arthritis and undifferentiated oligoarthritis and from healthy volunteers

Genetically determined differences in interleukin-10 (IL-10) and gamma interferon (IFN-gamma) responses in mice correlate with clearance of Chlamydia pneumonitis infection. We measured the synovial expression of IL-10 and IFN-gamma and additional cytokine genes in patients who had recent-onset Chlamydia-associated arthritis (Chl-AA). IL-10 and IFN-gamma mRNA were relatively abundant in recent-onset Chl-AA.

Differential Sensitivity of Distinct Chlamydia trachomatis Isolates to IFN-γ-Mediated Inhibition

Resistance to the mouse pneumonitis (MoPn) strain of Chlamydia trachomatis has been mapped to MHC class II-restricted, IL-12-dependent CD4+ T cells that secrete a type 1 profile of proinflammatory cytokines, which includes IFN-γ and TNF-α. The relative contribution of IFN-γ is controversial, however, due to variation in results presented by different laboratories. To determine whether C. trachomatis strain differences contributed to this apparent conflict, the relative resistance of IFN-γ-deficient mice to murine and human strains of C. trachomatis was compared. All human serovars were much more sensitive to the direct inhibitory actions of IFN-γ than the MoPn strain. Furthermore, genital clearance of human serovar D in the C57BL/6 mouse was mediated by class II-independent mechanisms that probably involved local production of IFN-γ by cells of the innate immune system. TNF-α also contributed indirectly to host resistance against all strains tested. The differential susceptibility of distinct C. trachomatis strains to effector cytokines such as IFN-γ could not have been predicted by interstrain biologic variation or by the profile of cytokines stimulated during infection. These findings indicate that strain variation should be considered in situations where related isolates of a given parasite produce conflicting data in models of infection and immunity. They also suggest that stimulation of mucosal IFN-γ activity is a relevant goal for a human chlamydial vaccine.

Reactive arthritis

Concepts about reactive arthritis are changing and must embrace consideration of the fact that bacteria or their products are present in the joint, not just at the portal of entry in the gastrointestinal (GI) or genitourinary (GU) tracts. With chlamydia-associated disease, atypical elementary bodies can be seen in synovium by electron microscopy, and nucleic acids, including RNA, can be found. It is not yet clear if bacterial nucleic acids are present in postenteric reactive arthritis and whether disease courses are predictably different after GI or GU infection. How bacteria are disseminated to joints and local factors, including cytokines that influence their persistence, are under study. Treatment with antibiotics may help some chlamydia-associated reactive arthritis but is not invariably effective.

Use of a live chlamydial vaccine to prevent ovine enzootic abortion

A lyophilised chlamydial vaccine was prepared from the 1B temperature-sensitive strain of ovine Chlamydia psittaci. Ewes inoculated with a low titre of the live vaccine four weeks before artificial insemination were challenged on day 70 of gestation with five UK field isolates of C psittaci, including strains A22 and S26/3 previously incorporated into a commercial inactivated vaccine. There was a significantly lower chlamydial abortion rate after challenge in the vaccinated group (7.1 per cent) than in the unvaccinated group (80 per cent). All the lambs born to the vaccinated ewes were viable and of good quality. The vaccine also reduced the number of infected ewes in the group and the severity of the infection. The compatibility of the chlamydial vaccine and a toxoplasma vaccine was also tested. The abortion rate of ewes vaccinated with the two vaccines at separate injection sites (16 per cent) was less than that of ewes vaccinated with both vaccines at one site (32 per cent).

Mucosal immunity in the human female reproductive tract: cytotoxic T lymphocyte function in the cervix and vagina of premenopausal and postmenopausal women

PROBLEM

To investigate the mucosal immune system in the cervix and vagina of premenopausal women in terms of immune cells present and cytolytic capacity of mucosal CD3+ T cells in the lower reproductive tract.

METHODS

Fresh tissue fragments prepared by vibratome sectioning were analyzed for the presence of cells by confocal scanning laser microscopy (CSLM). Isolated reproductive tract cells prepared by enzymatic were analyzed for CD3+ T cell phenotype by FACS analysis and for cytolytic function by an anti-CD3 mAb mediated redirected lysis assay.

RESULTS

As determined by CSLM, CD3+ cells as well as macrophages and dendritic cells are distributed throughout the lower female reproductive tract in both the epithelium and subepithelial mucosa. It was found that cervical and vaginal tissues from pre- and post-menopausal women contain CD3+ T cells (CTL) that have cytolytic activity, when measured in an antigen non-specific anti-CD3 mAb mediated redirected lysis assay.

CONCLUSIONS

These results indicate that the lower reproductive tract of women is immuno-competent as judged by the presence of CD3, CD4, CD8, macrophage, and dendritic cells in the endocervix, ectocervix, and vagina of premenopausal and postmenopausal women. Further, these studies demonstrate that CD3+ T cells with cytolytic activity are present in the cervix and vagina during the proliferative and secretory phases of the menstrual cycle and following menopause.

Cytotoxic-T-lymphocyte-mediated cytolysis of L cells persistently infected with Chlamydia spp

Persistent chlamydial infections have been proposed as a means whereby chlamydiae evade immune resolution of infection. Such a mechanism would require evasion not only of the humoral immune responses but also of cell-mediated immune responses. We hypothesized that if such a mechanism is important, persistently infected cells should not be recognized by cytotoxic T cells. Persistent infections were simulated in vitro by treatment of Chlamydia trachomatis- or Chlamydia psittaci-infected cells with gamma interferon (IFN-gamma), penicillin, or tryptophan depletion. Cultures were examined for induction of a chlamydial stress response (measured by transcription of groesl RNA) and for the effects on viability, infectivity, morphology, and immune recognition. Although both IFN-gamma and penicillin induced aberrant chlamydial morphology and growth, we did not find evidence that these treatments elicited a classical stress response. In addition, T-cell-mediated lysis of Chlamydia-infected target cells treated with IFN-gamma or penicillin or grown in tryptophan-deficient media was examined. The immune cell-mediated lysis of these treated infected cells demonstrated that despite the effects of these compounds on chlamydial growth and development, the infected cells continued to be efficiently recognized and killed by cytotoxic T cells. Thus, it seems unlikely that these in vitro models of persistence represent functional mechanisms to evade immune clearance.

Recombinant ovine interferon gamma inhibits the multiplication of Chlamydia psittaci in ovine cells

The local production of interferon-gamma (IFN-gamma) in sheep in response to Chlamydia psittaci was measured by cannulation of the efferent lymph duct draining the site of challenge inoculation. Peak production of IFN-gamma (256 U/ml) was detected 24 h after challenge. Based on these physiological data, functional studies were carried out in vitro to determine the effect of recombinant ovine (rOv) IFN-gamma on the multiplication of C. psittaci in ovine fibroblasts. IFN-gamma inhibited the multiplication of C. psittaci in ovine cells over a range of concentrations (250 U/ml to 2.5 U/ml) in a dose-dependent manner. The inhibition of chlamydial multiplication was most pronounced when cells were treated with rOvIFN-gamma for 24 h before infection. The addition of exogenous L-tryptophan (500 micrograms/ml) to cultures within 48th of infection abrogated the anti-chlamydial effect of rOvIFN-gamma thus suggesting that tryptophan deprivation is an anti-chlamydial mechanism induced by rOvIFN-gamma in these ovine cells.

Tryptophan depletion as a mechanism of gamma interferon-mediated chlamydial persistence

Previous studies have shown that the immune-regulated cytokine gamma interferon (IFN-gamma) activates host cells to restrict intracellular growth of the bacterial pathogen Chlamydia trachomatis by induction of the tryptophan-catabolizing enzyme indoleamine 2,3-dioxygenase (IDO). Recently, subinhibitory levels of IFN-gamma were used to generate an in vitro persistent chlamydial infection characterized by large aberrant, noninfectious reticulate bodies from which infectious progeny could be recovered following the removal of IFN-gamma. Studies were done to determine if the mechanism functioning to induce chlamydiae to enter a persistent state in the presence of low levels of IFN-gamma was similar to that reported to inhibit chlamydial growth. Host cells treated with levels of IFN-gamma required to induce persistence were assessed for IDO activity by high-performance liquid chromatography analysis of tryptophan and its catabolic products. Substantial tryptophan catabolism was detected in acid-soluble cellular pools, indicating that the intracellular availability of this essential amino acid was limited under these conditions. In addition, a mutant cell line responsive to IFN-gamma but deficient in IDO activity was shown to support C. trachomatis growth, but aberrant organisms were not induced in response to IFN-gamma treatment. Analyses of infected cells cultured in medium with incremental levels of exogenous tryptophan indicated that persistent growth was induced by reducing the amount of this essential amino acid. These studies confirmed that nutrient deprivation by IDO-mediated tryptophan catabolism was the mechanism by which IFN-gamma mediates persistent growth of C. trachomatis.

The importance of interferon-gamma in an early infection of Chlamydia psittaci in mice

Athymic mice (nu/nu) and their hairy littermates (nu/+) were infected experimentally with Chlamydia psittaci and the role of endogenous interferon-gamma (IFN-gamma) on the resolution of the infection was studied. The pathological changes produced in the spleen, liver and lung were exacerbated by administration of a monoclonal antibody (mAb) to IFN-gamma and an increased number of viable chlamydiae were recovered from the tissues of both nu/+ and nu/nu mice treated in this way.

Analysis of cytokine profiles in synovial T cell clones from chlamydial reactive arthritis patients: predominance of the Th1 subset

Subpopulations of human T cells (Th0, Th1 and Th2) can be distinguished by their cytokine-secretion pattern. Evidence is increasing from other studies that the outcome of a human disease may depend on the subpopulation of T cells that predominates at the site of inflammation. Reactive arthritis serves as a useful model of chronic inflammatory diseases, because the triggering antigen can be identified. Using this triggering antigen we raised 33 T cell clones reactive with Chlamydia trachomatis and 25 T cell clones that were not reactive, all from the synovial fluid of two patients suffering from Chlamydia-induced arthritis. Their cytokine secretion patterns for interferon-gamma (IFN-gamma), IL-2 and IL-4 were analysed, as also were mRNAs for IFN-gamma and IL-10 by in situ hybridization. Out of the 33 antigen-reactive clones 23 showed a Th1 pattern with IFN-gamma but not IL-4 secretion, while the remaining 10 exhibited a Th0 pattern. The clones that did not react with Chlamydia expressed all patterns of cytokine secretion, including a Th2 pattern, thus providing a control population that excludes bias in the sampling procedure. CD4 and CD8 clones displayed a similar cytokine-secretion pattern. In addition this study demonstrates for the first time the expression of IL-10 mRNA in T cell clones derived from synovial fluid, and this was not confined to the Th2 subset. The Th1 response that Chlamydia provoke can be regarded as appropriate for such an obligate intracellular pathogen.

Gamma interferon-induced nitric oxide production reduces Chlamydia trachomatis infectivity in McCoy cells

McCoy cells, murine-derived cells commonly used for propagation of chlamydiae, were found to be efficient producers of nitric oxide (NO) when primed with murine gamma interferon (IFN-gamma) and then exposed to the second signals provided by Escherichia coli lipopolysaccharide, human interleukin-1 alpha, murine tumor necrosis factor alpha, or Chlamydia trachomatis type H. Murine recombinant IFN-gamma over a range of 0 to 50 U/ml inhibited infectivity of C. trachomatis type H in a dose-dependent fashion in McCoy cells while simultaneously inducing NO production. Quantitation of infectious chlamydia progeny remaining in McCoy cells 48 or 72 h postinfection revealed that IFN-gamma-primed McCoy cells reduced chlamydial inclusion-forming units (expressed as units per milliliter) by 4 log10 units at higher IFN-gamma concentrations (50 U/ml) compared with control values. The magnitude of this antichlamydial effect was directly related to increased synthesis of NO, the production of which was IFN-gamma dose dependent. The antichlamydial effects of IFN-gamma were blocked in a dose-dependent manner by the addition of N-guanidino-monomethyl L-arginine (MLA), an inhibitor of nitric oxide synthesis. These results suggest that although IFN-gamma priming of McCoy cells is required for antichlamydial activity, nitric oxide is a necessary effector molecule involved in the mechanism(s) of IFN-gamma-induced inhibition of chlamydial proliferation in this murine cell line. The ability to block the potent antichlamydial effects of IFN-gamma by inhibition of a specific enzyme, nitric oxide synthase, may give insights into mechanisms by which IFN-gamma and perhaps other cytokines are able to control proliferation of chlamydiae and other intracellular pathogens.

Effects of immune activation on quinolinic acid and neuroactive kynurenines in the mouse

Accumulation of quinolinic acid and neuroactive kynurenines derived from tryptophan are of potential significance in human neuropathologic diseases because of their neurotoxic and convulsant properties. Clinical studies have established that sustained elevations of quinolinic acid, L-kynurenine and kynurenic acid within the cerebrospinal fluid occur in patients with a broad spectrum of inflammatory diseases and correlate with markers of immune activation and interferon-gamma activity. The present study describes an animal model that replicates these clinical observations and investigates the role of interferon-gamma as a mediator between immune activation and increased kynurenine pathway metabolism. Marked elevations in quinolinic acid, L-kynurenine and 3-hydroxykynurenine as well as an increased ratio of quinolinic acid: kynurenic acid in brain occurred 24 h after systemic pokeweed mitogen administration to C57BL6 mice. In plasma, L-tryptophan and kynurenic acid levels were reduced by pokeweed mitogen, while the concentrations of L-kynurenine, 3-hydroxykynurenine and quinolinic acid were increased. Interferon-gamma, pokeweed mitogen and lipopolysaccharide induced indoleamine-2,3-dioxygenase, the first enzyme of the kynurenine pathway, and increased both L-kynurenine and quinolinic acid concentrations of brain and systemic tissues, particularly in the lung, gastrointestinal tract and spleen. In contrast, hepatic tryptophan-2,3-dioxygenase activity was either reduced or unaffected. Increases in kynurenine pathway metabolism were sustained in mice given daily injections of interferon-gamma for seven days and subsequent responses to interferon-gamma were further enhanced. In contrast, daily administration of lipopolysaccharide was associated with subsequent attenuated responsiveness (tolerance) to lipopolysaccharide, pokeweed mitogen and interferon-gamma. Systemic administration of a monoclonal antibody to mouse interferon-gamma either attenuated or abolished the responses of kynurenine pathway metabolism to pokeweed mitogen and interferon-gamma. We conclude that acute and chronic increases in quinolinic acid and neuroactive kynurenines follow immune stimulation in mice, and result from indoleamine-2,3-dioxygenase induction. The results demonstrate that interferon-gamma is an important mediator between immune stimulation and indoleamine-2,3-dioxygenase induction. These increases in kynurenine pathway metabolism closely parallel the responses documented in patients with a broad spectrum of inflammatory diseases. Mice treated with immune stimuli are a useful model to investigate the relationships between immune activation and kynurenine pathway metabolism.

Protection against Chlamydia psittaci in mice conferred by Lyt-2+ T cells

A murine model was used to study the respective roles of L3T4+ and Lyt-2+ T cells in protection against Chlamydia psittaci. Donor mice were intravenously (i.v.) infected with 1 x 10(5) plaque-forming units (PFU) per mice of live C. psittaci. One month after inoculation, splenic cells from donors were transferred into syngenic recipients (5 x 10(7) cells/mouse). As measured by splenic colonization on Day 6 after i.v. challenge (1 x 10(5) PFU/mouse), transfer with primed (untreated) cells conferred a 3 log protection in this model. In vitro treatment, before transfer, of splenic cells with anti-Lyt-2 monoclonal antibody (mAb) and complement, markedly impaired the protection in comparison with control mice transferred with primed untreated cells, whereas treatment with anti-L3T4 mAb did not reduce the transferred protection. Resistance to a reinfection with C. psittaci was also studied after selective in vivo depletion of L3T4+ and Lyt-2+ T cells. One month after primary infection, mice were treated with anti-L3T4 or anti-Lyt-2 mAb and challenged thereafter (i.v., 1 x 10(5) PFU). The splenic colonization on Day 6 after challenge demonstrated that treatment with anti-Lyt-2 mAb impaired resistance against a subsequent infection with C. psittaci. Treatment with anti-L3T4 mAb in vivo had no effect on protection, as previously described in vitro. The mechanisms by which Lyt-2+ T cells could participate in the elimination of bacteria were discussed.

Interaction of chlamydiae and host cells in vitro

The obligately intracellular bacteria of the genus Chlamydia, which is only remotely related to other eubacterial genera, cause many diseases of humans, nonhuman mammals, and birds. Interaction of chlamydiae with host cells in vitro has been studied as a model of infection in natural hosts and as an example of the adaptation of an organism to an unusual environment, the inside of another living cell. Among the novel adaptations made by chlamydiae have been the substitution of disulfide-bond-cross-linked polypeptides for peptidoglycans and the use of host-generated nucleotide triphosphates as sources of metabolic energy. The effect of contact between chlamydiae and host cells in culture varies from no effect at all to rapid destruction of either chlamydiae or host cells. When successful infection occurs, it is usually followed by production of large numbers of progeny and destruction of host cells. However, host cells containing chlamydiae sometimes continue to divide, with or without overt signs of infection, and chlamydiae may persist indefinitely in cell cultures. Some of the many factors that influence the outcome of chlamydia-host cell interaction are kind of chlamydiae, kind of host cells, mode of chlamydial entry, nutritional adequacy of the culture medium, presence of antimicrobial agents, and presence of immune cells and soluble immune factors. General characteristics of chlamydial multiplication in cells of their natural hosts are reproduced in established cell lines, but reproduction in vitro of the subtle differences in chlamydial behavior responsible for the individuality of the different chlamydial diseases will require better in vitro models.

Interferon-gamma- and rickettsia-induced killing of macrophage-like cells is inhibited by anti-rickettsial antibodies and does not require the respiratory burst

The effects of antibiotics and anti-rickettsial antibodies on the ability of Rickettsia prowazekii to kill interferon-gamma (IFN-gamma)-treated macrophage-like RAW264.7 cells and the possible involvement of the macrophage respiratory burst in this killing were investigated. Rifampicin and chloramphenicol, antibiotics that inhibited rickettsial growth, did not inhibit the ability of the rickettsiae to kill IFN-gamma-treated RAW264.7 cells. However, pretreatment of R. prowazekii with anti-rickettsial IgG (which inhibits rickettsial growth in macrophage-like cells) inhibited the killing. This anti-rickettsial IgG did not inhibit association of the rickettsiae with the cells. Although untreated and IFN-gamma-treated RAW264.7 cells underwent a respiratory burst when exposed to a stimulant such as opsonized zymosan or phorbol myristate acetate (PMA), infection of such cells with R. prowazekii was not associated with a measurable respiratory burst, as determined by monitoring hydrogen peroxide (H2O2) production and hexose monophosphate shunt activity. Furthermore, a variant macrophage-like cell line (J774.C3C) which lacks the ability to undergo a respiratory burst was killed by the combination of IFN-gamma treatment and R. prowazekii infection. These data define three interesting features of the killing of macrophage-like cells by IFN-gamma and R. prowazekii: (i) the macrophage respiratory burst is not required; (ii) anti-rickettsial antibiotics are not inhibitory; and (iii) anti-rickettsial antibodies are inhibitory.