Polymorphonuclear neutrophils are necessary for the recruitment of CD8(+) T cells in the liver in a pregnant mouse model of Chlamydophila abortus (Chlamydia psittaci serotype 1) infection

The Immune Response in the Uteri and Placentae of Chlamydia abortus-Infected Ewes and Its Association with Pregnancy Outcomes

The enzootic abortion of ewes, caused by the bacterium Chlamydia abortus (C. abortus), is one of the main causes of abortion in sheep. There are multiple contributory factors, including chlamydial growth, host immune response, and hormonal balance, that result in different pregnancy outcomes, such as abortion, the birth of weak lambs that may die, or healthy lambs. This study aimed to determine the relationship between phenotypical patterns of immune cell infiltration and different pregnancy outcomes in twin-bearing sheep (both lambs born dead; one alive and one dead; both alive) when experimentally infected with C. abortus. Both the sheep uteri and placentae were collected after parturition. All samples were analysed for specific immune cell features, including cell surface antigens and the T-regulatory (Treg) cell-associated transcription factor and cytokines, by immunohistochemistry and in situ hybridisation. Some of these immunological antigens were evaluated in ovine reproductive tissues for the first time. Differential patterns of T helper/Treg cells revealed significant group effects in the placentae. It suggests the potential role that the balance of lymphocyte subsets may play in affecting different pregnancy outcomes in C. abortus-infected sheep. The present study provides novel detailed information about the immune responses observed at the maternofoetal interface in sheep at the time of pre-term abortion or lambing.

Recent advances and public health implications for environmental exposure to Chlamydia abortus: from enzootic to zoonotic disease

Environmental transmission of Chlamydia abortus as a result of enzootic disease or disease outbreaks and the threats posed by this pathogen has been previously reported, however a state-of-the-science review of these reports and the identification of future research priorities in this area is still lacking. This study provides an overview of the current knowledge of host–pathogen–environment interactions, addressing public health risks and identifying critical questions and research gaps. We performed a systematic PubMed and Web of Science search for publications related to Chlamydia abortus in the past four decades, and we reviewed and combined the evidence critically discussing and commenting the results. A total of 182 studies, 5 chapters of specific books and the “OIE terrestrial manual” were included in this review. There were substantial variations between the studies in topic addressed and experimental design. Overall, the literature largely supports the crucial role played by environmental exposure on the acquisition of zoonotic disease caused by Chlamydia abortus. We also identify the paucity of information related to interspecies transmission and pathogen adaptation in relation to environmental dissemination and zoonotic risk. This analysis further highlights the need for additional research given that environmental transmission represents a serious risk not only to susceptible patients (pregnant women and immunocompromised individuals), but also for other species including wildlife.

The Spatial Distribution of Immune Cell Subpopulations in Hepatocellular Carcinoma

Infiltrating immune cells in the tumor microenvironment (TME) influence tumor progression and patient prognosis, making them attractive therapeutic targets for immunotherapy research. A deeper understanding of immune cell distributions in the TME in hepatocellular carcinoma (HCC) is needed to identify interactions among different immune cell types that might impact the effectiveness of potential immunotherapies. We performed multiplex immunohistochemistry using a tissue microarray of samples from 302 patients with HCC to elucidate the spatial distributions of immune cell subpopulations (CD3⁺, CD4⁺, CD8⁺, CD66b⁺, and CD68⁺) in HCC and normal liver tissues. We analyzed the associations between different immune subpopulations using Pearson's correlation. G(r) functions, K(r) functions and Euclidean distance were applied to characterize the bivariate distribution patterns among the immune cell types. Cox regression and Kaplan‐Meier analysis were used to evaluate the associations between tumor infiltration by different immune cells and patient outcomes after curative surgery. We also analyzed the relationship between the spatial distribution of different immune cell subpopulations with HCC patient prognosis. We found that the immune cell spatial distribution in the HCC TME is heterogeneous. Our study provides a theoretical basis for HCC immunotherapy.

Effect of progesterone on the vaccination and immune response against Chlamydia abortus in sheep

Chlamydia abortus produces ovine enzootic abortion (OEA). Symptoms are not observed until the organism colonises the placenta, eventually causing abortion. Infected animals become carriers and will shed the organism in the following oestruses. This process suggests that sex hormones might play an important role in the physiopathology of OEA, affecting the success of chlamydial clearance and also jeopardising the effectiveness of vaccination. However, the mechanisms through which sex hormones are involved in chlamydial pathogenicity remain unclear. The aim of this study, therefore, was to determine the effect of progesterone on the immune response against C. abortus and on the protection conferred by an experimental inactivated vaccine in sheep. Eighteen sheep were ovariectomised and divided into four groups: vaccinated and progesterone-treated (V-PG), vaccinated and non-treated (V-NT), non-vaccinated and non-treated (NV-NT) and non-vaccinated and progesterone-treated sheep (NV-PG). Animals from both PG groups were treated with commercial medroxyprogesterone acetate impregnated intravaginal sponges before and during the vaccination (V-PG) or just before challenge (NV-PG). The animals from both V groups were subcutaneously immunised with an experimental inactivated vaccine, which was seen to confer high protection in previous studies. All sheep were challenged intratracheally with C. abortus strain AB7 and were sacrificed on day 8 post-infection. Morbidity was measured as the variation in rectal temperature and samples of sera were collected for antibody and cytokine (IFN-γ and IL-10) analysis by commercial ELISA. In addition, lung and lymph node samples were collected for chlamydial detection by qPCR and for histopathological and immunohistochemical analyses. Sheep from the V-PG group showed less severe or no lesions and lower morbidity than the other groups. They also had the highest abundance of regulatory T-cells. The sheep from V-NT also manifested high antibody levels against C. abortus and less severe lesions than those observed in non-vaccinated sheep, which showed high morbidity, low antibody levels and severe lesions, especially in NV-NT. These results confirm the effectiveness of the experimental vaccine employed and suggest that progesterone could enhance the effect.

Development of an in vivo model of Chlamydia abortus chronic infection in mice overexpressing IL-10

Chlamydia abortus, like other members of the family Chlamydiaceae, have a unique intracellular developmental cycle that is characterized by its chronic nature. Infection of a flock can remain undetected for months, until abortion occurs the following reproductive season but, to date, neither the location nor the mechanisms that maintain this latent phase are fully understood. Studies have shown that IL-10 produced as a response to certain micro-organisms sustains the intracellular survival of pathogens and increases host susceptibility to chlamydial infections. In order to induce a sustained infection C. abortus, transgenic mice that constitutively express IL-10 were infected and the immunological mechanisms that maintain infection in these mice were compared with the mechanisms of a resistant wild-type mouse strain. Viable bacteria could be detected in different tissues of transgenic mice up to 28 days after infection, as analysed by bacterial isolation and immunohistochemistry. Chronic infection in these mice was associated with an impaired recruitment of macrophages, decreased iNOS activity at the site of infection and a more diffuse distribution of inflammatory cells in the liver. This murine model can be of great help for understanding the immunological and bacterial mechanisms that lead to chronic chlamydial infections.

Kinetics of Infection and Effects on the Placenta of Clamydophila abortus in Experimentally Infected Pregnant Ewes

A Chlamydophila abortus-induced abortion model was carried out on the basis of the experimental infection of ewes at day 75 of gestation. The infection induced abortions and the birth of weak lambs during the last 3 weeks of pregnancy. To study the kinetics of the infection in the placenta and in other organs, infected ewes were killed at 105, 120, and 130 days of gestation and also several days after abortion or parturition. Infected ewes developed a systemic infection that caused a mild and transient pneumonia and focal hepatitis. Pathologic changes were observed in placentas at 120 day of gestation, although the lesions varied between animals and even between placentomes of the same placenta. The first placental area infected was the maternal stroma and epithelium next to the intercaruncular areas, where neutrophilic response seemed to control the infection. A substantial degree of multiplication of C. abortus was then observed in the trophoblast cells of the placentome, periplacentomal choriallantoic membranes, and hilius, with an inflammatory exudate composed mainly of neutrophils, some macrophages, and very scarce lymphocytes. After abortion, the lesions affected the intercotyledonary areas of the aborted placentas, whereas in the uterus significant lymphocyte infiltration was observed, together with a rapid decrease of the C. abortus antigen in the degenerated caruncular tissues.

Neutrophil trails guide influenza-specific CD8⁺ T cells in the airways

During viral infections, chemokines guide activated effector T cells to infection sites. However, the cells responsible for producing these chemokines and how such chemokines recruit T cells are unknown. Here, we show that the early recruitment of neutrophils into influenza-infected trachea is essential for CD8(+) T cell-mediated immune protection in mice. We observed that migrating neutrophils leave behind long-lasting trails that are enriched in the chemokine CXCL12. Experiments with granulocyte-specific CXCL12 conditionally depleted mice and a CXCR4 antagonist revealed that CXCL12 derived from neutrophil trails is critical for virus-specific CD8(+) T cell recruitment and effector functions. Collectively, these results suggest that neutrophils deposit long-lasting, chemokine-containing trails, which may provide both chemotactic and haptotactic cues for efficient CD8(+) T cell migration and localization in influenza-infected tissues.

Differential infiltration of neutrophils in T1-T2 versus T3-T4 oral squamous cell carcinomas: a preliminary study

Background

Recent studies have pointed towards a role of tumour-infiltrating neutrophils in cancer biology. Investigations on oral squamous cell carcinoma have indicated a possible association with clinical characteristics. This study aimed to evaluate neutrophil infiltration and the neutrophil/lymphocyte ratio in the central areas and invasive front of oral squamous cell carcinomas at different T stages, and their association with clinicopathological features and patient outcome.

Methods

Clinical information was retrieved from the charts of patients who had undergone surgical treatment. Samples of the excised tumours were subjected to immunohistochemical analysis for CD66b and CD3. Semi-quantitative analysis was performed in the intratumoural region and in the invasive front. Appropriate statistical tests were used for evaluating the data, including Kaplan–Meier survival analysis and the log-rank test. A p value of less than 0.05 was considered significant.

Results

T3–T4 tumours presented higher CD66b infiltration in the intratumoural region and higher CD66b/CD3 ratios in the invasive front than T1–T2 lesions (p < 0.05). There was a strong inverse correlation between CD66b and CD3 in the invasive front of T3–T4 tumours (r = −0.712, p < 0.05). Comparisons of CD66b and the CD66b/CD3 ratio according to N status, tumour location, recurrence, inflammation grade, and histological grade did not reach statistical significance. Survival analysis also did not show any significant differences.

Conclusions

The present study showed different degrees of neutrophil infiltration between T1–T2 and T3–T4 oral cancers, with higher indexes in the advanced lesions. However, there was no association with clinicopathological features or with time to recurrence.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-015-1541-x) contains supplementary material, which is available to authorized users.

Enhanced neutrophil longevity and recruitment contribute to the severity of oviduct pathology during Chlamydia muridarum infection

Our previous studies revealed that intravaginal infection of mice with a plasmid-deficient strain of Chlamydia muridarum, CM3.1, does not induce the development of oviduct pathology. In this study, we determined that infection with CM3.1 resulted in a significantly reduced frequency and absolute number of neutrophils in the oviducts during acute infection. This reduction in neutrophils was associated with significantly lower levels of neutrophil chemokines in the oviducts and decreased production of neutrophil chemokines by oviduct epithelial cells infected with CM3.1 in vitro. Infection with CM3.1 also resulted in an increased frequency of late apoptotic/dead neutrophils in the oviduct. Examination of the ability of Chlamydia trachomatis to prevent neutrophil apoptosis in vitro revealed that C. trachomatis strain D/UW-3/Cx exhibited an enhanced ability to prevent neutrophil apoptosis compared to plasmid-deficient CTD153, and this effect was dependent on the presence of CD14(high) monocytes. The presence of monocytes also resulted in enhanced neutrophil cytokine production and increased production of tissue-damaging molecules in response to D/UW-3/Cx relative to results with CTD153. Attempts to use antibody-mediated depletion to discern the specific role of neutrophils in infection control and pathology in vivo revealed that although Ly6G(high) neutrophils were eliminated from the blood and oviducts with this treatment, immature neutrophils and high levels of tissue-damaging molecules were still detectable in the upper genital tract. These data support the role of neutrophils in chlamydia-induced pathology and reveal that novel methods of depletion must be developed before their role can be specifically determined in vivo.

Neutrophils sustain effective CD8(+) T-cell responses in the respiratory tract following influenza infection

Neutrophils have an important role in early host protection during influenza A virus infection. Their ability to modulate the virus-specific adaptive immune response is less clear. Here, we have used a mouse model to examine the impact of neutrophils on CD8(+) T-cell responses during influenza virus infection. CD8(+) T-cell priming, expansion, migration, cytokine secretion and cytotoxic capacity were investigated in the virus-infected airways and secondary lymphoid organs. To do this, we utilised a Ly6G-specific monoclonal antibody (mAb; 1A8) that specifically depletes neutrophils in vivo. Neutrophil depletion early after infection with influenza virus strain HKx31 (H3N2) did not alter influenza virus-derived antigen presentation or naïve CD8(+) T-cell expansion in the secondary lymphoid organs. Trafficking of virus-specific CD8(+) T cells into the infected pulmonary airways was also unaltered. Instead, early neutropenia reduced both the overall magnitude of influenza virus-specific CD8(+) T cells, together with impaired cytokine production and cytotoxic effector function. Therefore, neutrophils are important participants in anti-viral mechanisms that sustain effective CD8(+) T-cell responses in the respiratory tract of influenza virus-infected mice.

Intratumoral neutrophils: a poor prognostic factor for hepatocellular carcinoma following resection

BACKGROUND & AIMS

Neutrophil infiltration has been linked to clinical outcome of various cancer types. However, its role in hepatocellular carcinoma (HCC) is unclear. In this study, we investigated prognostic values for intratumoral and peritumoral neutrophils in HCC patients undergoing curative resection.

METHODS

The expression of CD66b, CD8, TGF-beta, and CD34 was assessed by immunohistochemistry in tissue microarrays containing paired intratumoral and peritumoral tissues from 197 patients receiving curative resection for HCC. Prognostic values for these and other clinicopathologic factors were evaluated.

RESULTS

Intratumoral CD66b(+) neutrophils significantly correlated with CD8(+) T cells (r=0.240, p=0.004), TGF-beta expression (p=0.012), BCLC stage (p=0.016), and early recurrence (p=0.041). Increased intratumoral neutrophils were significantly associated with decreased RFS/OS (p=0.001 and p<0.001, respectively) in univariate analysis and were identified as an independent prognostic factor (HR=1.845, 95% CI=1.169-2.911, p=0.008 for RFS; HR=2.578, 95% CI=1.618-4.106, p<0.001 for OS) in multivariate analysis. Intratumoral neutrophil-to-CD8(+) T cell ratio (iNTR) better predicted the outcome in terms of minimum p values. Intratumoral neutrophils were also demonstrated to be statistically predictive for RFS/OS in the normal AFP subgroup, small HCC subgroup, and validation cohort. However, peritumoral neutrophils were not associated with the outcome of HCC.

CONCLUSIONS

The presence of intratumoral neutrophils was a poor prognostic factor for HCC after resection. Intratumoral neutrophil-to-CD8(+) T cell ratio was a better predictor of outcome.

Human conjunctival transcriptome analysis reveals the prominence of innate defense in Chlamydia trachomatis infection

Trachoma is the leading infectious cause of blindness and is endemic in 52 countries. There is a critical need to further our understanding of the host response during disease and infection, as millions of individuals are still at risk of developing blinding sequelae. Infection of the conjunctival epithelial cells by the causative bacterium, Chlamydia trachomatis, stimulates an acute host response. The main clinical feature is a follicular conjunctivitis that is incompletely defined at the tissue-specific gene expression and molecular levels. To explore the features of disease and the response to infection, we measured host gene expression in conjunctival samples from Gambian children with active trachoma and healthy controls. Genome-wide expression and transcription network analysis identified signatures characteristic of the expected infiltrating immune cell populations, such as neutrophils and T/B lymphocytes. The expression signatures were also significantly enriched for genes in pathways which regulate NK cell activation and cytotoxicity, antigen processing and presentation, chemokines, cytokines, and cytokine receptors. The data suggest that in addition to polymorph and adaptive cellular responses, NK cells may contribute to a significant component of the conjunctival inflammatory response to chlamydial infection.

Potential role of decoy B7-H4 in the pathogenesis of rheumatoid arthritis: a mouse model informed by clinical data

BACKGROUND

A pathogenic hallmark of rheumatoid arthritis (RA) is persistent inflammatory responses in target tissues and organs. Immune responses mediated by T cells and autoantibodies are known to play pivotal roles. A possible interpretation for this observation is a loss of negative regulation of autoimmune responses. Here we sought to investigate whether B7-H4, a cell surface inhibitory molecule of the B7-CD28 signaling pathway, may play a role in the pathogenesis of RA.

METHODS AND FINDINGS

In a cross-sectional study of a clinical convenience sample using monoclonal antibodies against human B7-H4 molecules, we detected high levels of the soluble form of B7-H4 (sH4) in the sera of 65% of patients with RA (n = 68) versus only 13% of healthy donors (n = 24). Elevated sH4 was associated with an increased disease severity score (DAS28) in a cross-sectional analysis. In a mouse model of RA, transgenic expression of sH4 or genetic deletion of B7-H4 accelerated the progression of collagen-induced arthritis, accompanied by enhanced T and B cell-mediated autoimmune responses as well as increased activity of neutrophils. Expression in vivo of an agonist, a B7-H4-immunoglobulin Fc fusion protein, profoundly suppressed disease progression in the mouse model.

CONCLUSIONS

Our findings in mice indicate that sH4 acts as a decoy molecule to block the inhibitory functions of cell-surface B7-H4, leading to exacerbation of collagen-induced arthritis. If the preliminary correlation between sH4 levels and disease activity in patients with RA can be confirmed to reflect a similar mechanism, these findings suggest a novel target for treatment approaches. Please see later in the article for the Editors' Summary.

Critical role of IL-17RA in immunopathology of influenza infection

Acute lung injury due to influenza infection is associated with high mortality, an increase in neutrophils in the airspace, and increases in tissue myeloperoxidase (MPO). Because IL-17A and IL-17F, ligands for IL-17 receptor antagonist (IL-17RA), have been shown to mediate neutrophil migration into the lung in response to LPS or Gram-negative bacterial pneumonia, we hypothesized that IL-17RA signaling was critical for acute lung injury in response to pulmonary influenza infection. IL-17RA was critical for weight loss and both neutrophil migration and increases in tissue myeloperoxidase (MPO) after influenza infection. However, IL-17RA was dispensable for the recruitment of CD8(+) T cells specific for influenza hemagglutinin or nucleocapsid protein. Consistent with this, IL-17RA was not required for viral clearance. However, in the setting of influenza infection, IL-17RA(-/-) mice showed significantly reduced levels of oxidized phospholipids, which have previously been shown to be an important mediator in several models of acute lung injury, including influenza infection and gastric acid aspiration. Taken together, these data support targeting IL-17 or IL-17RA in acute lung injury due to acute viral infection.

B cells are essential for moderating the inflammatory response and controlling bacterial multiplication in a mouse model of vaccination against Chlamydophila abortus infection

The use of inactivated vaccines associated with suitable adjuvants has been demonstrated to confer a good level of protection against Chlamydophila abortus. However, the basis of the immune protective response induced by these vaccines has been poorly studied. B cells act as an immune regulatory population during primary infection by C. abortus. Thus, it was considered of interest to study the role of B cells in an infection after immunization with a killed vaccine. For this, C57BL/6 and B-cell-deficient mice were immunized with a killed vaccine against C. abortus using QS-21 as the adjuvant. After challenge, the course of infection was established by analysis of morbidity, C. abortus burden in the liver, and histopathological changes. The immune response induced was studied by real-time PCR techniques. Experiments involving transfer of immune serum from vaccinated or previously infected mice were also carried out. The lack of B cells reduced the protection conferred by the QS-21 adjuvant vaccine. Vaccinated B-cell-deficient mice showed a 1,000-fold-greater bacterial burden in the liver than their wild-type counterparts. Obvious differences existed in the liver, where a severe neutrophilic reaction and extended areas of necrosis were observed with vaccinated B-cell-deficient mice. An analysis of the immune response pointed to a significant increase in inflammatory cytokines and chemokines and the deficient production of transforming growth factor beta. The transfer of antibodies restored the level of protection. This study demonstrates that B cells play a crucial role in controlling C. abortus multiplication and prevent an exacerbated inflammatory response.

Chlamydophila abortus infection in the mouse: a useful model of the ovine disease

Chlamydophila (C.) abortus is an obligate intracellular bacterium able to colonize the placenta of several species of mammals, which may induce abortion in the last third of pregnancy. The infection affects mainly small ruminants resulting in major economic losses in farming industries worldwide. Furthermore, its zoonotic risk has been reported in pregnant farmers or abattoir workers. Mouse models have been widely used to study both the pathology of the disease and the role of immune cells in controlling infection. Moreover, this animal experimental model has been considered a useful tool to evaluate new vaccine candidates and adjuvants that could prevent abortion and reduce fetal death. Future studies using these models will provide and reveal information about the precise mechanisms in the immune response against C. abortus and will increase the knowledge about poorly understood issues such as chlamydial persistence.

Role of CD8(+)T cells in the host response to Chlamydia

Chlamydia infections constitute a major public health problem. Although multiple arms of the immune system participate in the control of Chlamydia in infected hosts, T lymphocytes are essential. This review focuses on the roles that CD8(+)T cells may play in immunoprotection and immunopathology following recognition of Chlamydia-infected cells.

The role of neutrophils in the upper and lower respiratory tract during influenza virus infection of mice

Background

Neutrophils have been shown to play a role in host defence against highly virulent and mouse-adapted strains of influenza virus, however it is not clear if an effective neutrophil response is an important factor moderating disease severity during infection with other virus strains. In this study, we have examined the role of neutrophils during infection of mice with influenza virus strain HKx31, a virus strain of the H3N2 subtype and of moderate virulence for mice, to determine the role of neutrophils in the early phase of infection and in clearance of influenza virus from the respiratory tract during the later phase of infection.

Methods

The anti-Gr-1 monoclonal antibody (mAb) RB6-8C5 was used to (i) identify neutrophils in the upper (nasal tissues) and lower (lung) respiratory tract of uninfected and influenza virus-infected mice, and (ii) deplete neutrophils prior to and during influenza virus infection of mice.

Results

Neutrophils were rapidly recruited to the upper and lower airways following influenza virus infection. We demonstrated that use of mAb RB6-8C5 to deplete C57BL/6 (B6) mice of neutrophils is complicated by the ability of this mAb to bind directly to virus-specific CD8⁺ T cells. Thus, we investigated the role of neutrophils in both the early and later phases of infection using CD8⁺ T cell-deficient B6.TAP^-/- mice. Infection of B6.TAP^-/- mice with a low dose of influenza virus did not induce clinical disease in control animals, however RB6-8C5 treatment led to profound weight loss, severe clinical disease and enhanced virus replication throughout the respiratory tract.

Conclusion

Neutrophils play a critical role in limiting influenza virus replication during the early and later phases of infection. Furthermore, a virus strain of moderate virulence can induce severe clinical disease in the absence of an effective neutrophil response.

Neutrophils and intracellular pathogens: beyond phagocytosis and killing

Neutrophils are not simply scavenging phagocytes that clear extracellular spaces of rapidly proliferating microbes; they are also active in the control of infections by intracellular pathogens. Several mechanisms for nonphagocytic roles of neutrophils in protective immunity have been put forth over the years but further evidence has recently been accumulating at an increasing pace. In this review, I present the evidence that suggests neutrophils are involved in pathogen shuttling into the lymphoid tissues, in antigen presentation, and in early T cell recruitment and initiation of granuloma organization. Also, a clearer view on the antimicrobial molecules that can be acquired by macrophages to enhance their antimicrobial activity is now emerging. Finally, neutrophils can adversely affect immunity against certain parasites by causing immune deviation.

Experimental Coxiella burnetii infection in pregnant goats: a histopathological and immunohistochemical study

Pregnant goats were inoculated subcutaneosly with Coxiella burnetii and the course of infection was studied. Abortion in the last third of pregnancy occurred in all infected animals. Tissues from the placenta and other organs were studied before and after abortion by immunohistochemistry and PCR analysis. After infection, mild lesions were observed in several maternal organs, mainly the mammary gland but also the lung and the liver. The trophoblast cells of the choriallantoic membrane were the first target cells of the placenta; there was, however, a substantial delay between initial infection and placental colonization. In the last weeks of pregnancy, just before abortion, massive bacterial multiplication was detected in the placenta. In this stage of infection a necrotic and suppurative placentitis separated the fetal trophoblast cells from maternal syncytial epithelium. Vasculitis was observed in the fetal mesenchyme. A strong maternal T-cell response was detected in the inter-placentomal areas but not in the placentomes, where only neutrophils and smaller numbers of macrophages were associated with the lesions. Neither lesions nor C. burnetii DNA were found in maternal organs in animals maintained until day 120 post-abortion.

Characterization of a murine model of intranasal infection suitable for testing vaccines against C. abortus

Mouse models have been widely used to test candidate vaccines against Chlamydophila abortus infection in mice. Although the induction of a systemic infection by endogenous or intraperitoneal inoculation is a useful tool for understanding the immune mechanism involved in the protection conferred by the vaccination, a different approach is necessary to understand other factors of the infection, such as mucosal immunity or the colonization of target organs. To test whether C. abortus intranasal model of infection in mice is a useful tool for testing vaccines in a first group of experiments mice, were infected intranasally with C. abortus to characterize the model of infection. When this model was used to test vaccines, two inactivated experimental vaccines, one of them adjuvated with QS-21 and another with aluminium hydroxide, and a live attenuated vaccine (strain 1B) were used. Non-vaccinated control mice died within the first 8 days, after displaying substantial loss of weight. Histologically, the mice showed lobar fibrinopurulent bronchointerstitial pneumonia. Prior immunization with QS-21 adjuvated vaccine or 1B vaccine presented mortality and the recipients showed a greater number of T cells in the lesions, especially CD8(+) T cells, than the control mice and mice immunized with vaccine adjuvated with aluminium hydroxide. The results confirm that the C. abortus intranasal model of infection in mice is a useful tool for testing vaccines.

Role of polymorphonuclear neutrophils (PMNs) and NK cells in the protection conferred by different vaccines against Chlamydophila abortus infection

Ovine enzootic abortion (OEA) is caused by Chlamydophila abortus, an intracellular bacterium which acts by infecting the placenta, causing abortion in the last term of gestation. The main prevention strategy against OEA is the vaccination of flocks. An effective vaccine against C. abortus must induce a Th1-like specific immune response, which is characterized by the early production of IFN-gamma and the activation of CD8(+)T cells. Moreover, vaccine effectiveness could be modulated by the functioning of the innate immunity. The purpose of this study was to ascertain how polymorphonuclear neutrophils (PMNs) and NK cells might influence vaccine-induced protection. The live attenuated 1B vaccine and two inactivated experimental vaccines, adjuvated with aluminium hydroxide (AH) or QS-21 (QS), were used in PMN-depleted or NK cell-depleted mice. For PMN depletion, RB6-8C5 monoclonal antibody, which recognizes GR1(+) receptors (Robben, P.M., LaRegina, M., Kuziel, W.A., Sibley, L.D. 2005. Recruitment of Gr-1(+) monocytes is essential for control of acute toxoplasmosis. The Journal of Experimental Medicine 201, 1761-1769.) was used, while for NK cell-depletion the anti-asialo GM1 polyclonal antibody was used. The depletion of PMNs caused 100% mortality in non-vaccinated mice (NV) and 60% mortality in the AH-vaccinated mice by day 10 p.i., while both groups showed a significant increase in their bacterial burden in the liver by day 4 p.i. The depletion of NK cells caused mortality only in the NV group (50% by day 10 p.i.), although this group and the 1B vaccinated mice showed an increased bacterial burden in the liver at day 4 p.i. Our results suggest that the importance of PMNs in inactivated vaccines depends on the adjuvant chosen. The results also demonstrated that the importance of NK cells is greater in live vaccines than in inactivated vaccines.

Both influenza-induced neutrophil dysfunction and neutrophil-independent mechanisms contribute to increased susceptibility to a secondary Streptococcus pneumoniae infection

Since secondary Streptococcus pneumoniae infections greatly increase the mortality of influenza infections, we determined the relative roles of neutrophil-dependent and -independent mechanisms in increased susceptibility to S. pneumoniae during influenza infection. Mice infected with influenza for 6 days, but not 3 days, showed a significant increase in susceptibility to S. pneumoniae infection compared to mice not infected with influenza. There was significant neutrophil accumulation in the lungs of S. pneumoniae-infected mice regardless of whether or not they were infected with influenza for 3 or 6 days. Depletion of neutrophils in these mice resulted in increased susceptibility to S. pneumoniae in both the non-influenza-infected mice and mice infected with influenza for 3 days but not in the mice infected with influenza for 6 days, indicating that a prior influenza infection of 6 days may compromise neutrophil function, resulting in increased susceptibility to a S. pneumoniae infection. Neutrophils from the lungs of mice infected with influenza for 3 or 6 days exhibited functional impairment in the form of decreased phagocytosis and intracellular reactive oxygen species generation in response to S. pneumoniae. In addition, neutrophil-depleted mice infected with influenza for 6 days were more susceptible to S. pneumoniae than neutrophil-depleted mice not infected with influenza, indicating that neutrophil-independent mechanisms also contribute to influenza-induced increased susceptibility to S. pneumoniae. Pulmonary interleukin-10 levels were increased in coinfected mice infected with influenza for 6 days but not 3 days. Thus, an influenza infection of 6 days increases susceptibility to S. pneumoniae by both suppression of neutrophil function and by neutrophil-independent mechanisms such as enhanced cytokine production.

Granulocyte colony-stimulating factor and neutrophils—forgotten mediators of inflammatory disease

Recent studies have highlighted the functional capacity of neutrophils as powerful mediators of tissue inflammation. Granule-packaged proteases and reactive oxygen intermediates, which are important for intracellular digestion during phagocytosis, are released from neutrophils during inflammation. In the extracellular environment, neutrophil-derived proteases can cause local tissue damage, but also regulate the activity of cytokines, cytokine receptors and chemokines. Neutrophils can themselves produce an array of inflammatory mediators, including cytokines, chemokines and complement; these cells also express Fc receptors, which can bind and possibly transport immune complexes into the extravascular compartment, as well as activating neutrophils at opsonised surfaces. Blood-borne neutrophils interact with, and then exit through, the endothelium of blood vessels, after which these cells die and must be removed safely. The balance between neutrophil survival and clearance is crucial to the resolution of inflammation. A major regulator of neutrophil production and survival is the cytokine granulocyte colony-stimulating factor (G-CSF). Treatment with G-CSF can exacerbate underlying inflammatory diseases in humans and mice, and G-CSF deficiency is profoundly protective against collagen-induced arthritis in mice. These findings implicate G-CSF as an important proinflammatory cytokine. This article discusses the roles of neutrophils and G-CSF during chronic inflammatory diseases.

Comparison of Fetal and Maternal Inflammatory Responses in the Ovine Placenta after Experimental Infection with Chlamydophila abortus

Placentae from 13 pregnant ewes infected intravenously with Chlamydophila abortus, together with placentae from nine uninfected control ewes, were examined at 14, 21 or 28 days post-inoculation (p.i.). Chlamydial inclusions were present in the trophoblast at 14 days p.i. and were widespread by 21 days p.i. Chorioallantoic lesions (oedema, arteritis and thrombosis) were severe at 28 days p.i., the changes being particularly marked in the membrane surrounding placentomes. Lymphocytes constituted only a small proportion of the cellular infiltrate in the chorioallantois; neutrophil infiltration of the chorionic surface was evident where the trophoblast layer had sloughed, whereas macrophages represented the predominant cell type in the deeper stroma. In contrast, on the maternal side of the placenta, chlamydial inclusions were sparse at all timepoints, and even at 28 days p.i., lesions were restricted to focal endometritis at the placentomal limbus and occasional foci of septal necrosis. T lymphocytes were numerous within endometrial and septal lesions, the infiltrate consistently containing more CD8(+) than CD4(+) cells. The fetal response to chlamydial invasion of the placenta was innate in character, whereas the maternal response appeared to represent an acquired, chlamydia-specific immune response.

Relative importance of CD4+ and CD8+ T cells in the resolution of Chlamydophila abortus primary infection in mice

The role of the specific cellular immune response is well established in Chlamydiaceae infections, but the importance of each T-cell subset seems to be species-dependent. This study was designed to clarify the role of T-cell subsets in the response to Chlamydophila abortus primary infection. C57BL/6 mice were depleted of CD4+ or CD8+, or both, by monoclonal antibody injections and subsequently infected with C. abortus. Mice were killed at intervals and samples were collected for bacteriological and histopathological analysis. Also carried out were spleen cell culture, cytokine quantification, immunolabelling for C. abortus antigen, and a TUNEL assay for apoptosis. CD8+ T cell-depleted mice all died within 12 days of C. abortus infection, while no mortality was observed in the other groups; surprisingly, CD4+ T cell-depleted mice showed lower morbidity (expressed as weight loss) than did a non-depleted (control) group. CD8+ T cell-depleted mice also differed from the other groups in showing a significantly higher chlamydial burden in the liver. CD8+ T cell-depleted mice also had a higher number of apoptotic cells in hepatic inflammatory foci and showed exacerbated IFN-gamma production by spleen cells after specific stimulation. Simultaneous depletion of both T-cell subpopulations led to a chronic infection, but not to early mortality. It is concluded that CD8+ T cells may play a role in the regulatory control of the CD4+ T-cell response and may have a direct cytotoxic or IFN-gamma-mediated effect on infected cells.

Roles of macrophages and neutrophils in the early host response to Bacillus anthracis spores in a mouse model of infection

The development of new approaches to combat anthrax requires that the pathogenesis and host response to Bacillus anthracis spores be better understood. We investigated the roles that macrophages and neutrophils play in the progression of infection by B. anthracis in a mouse model. Mice were treated with a macrophage depletion agent (liposome-encapsulated clodronate) or with a neutrophil depletion agent (cyclophosphamide or the rat anti-mouse granulocyte monoclonal antibody RB6-8C5), and the animals were then infected intraperitoneally or by aerosol challenge with fully virulent, ungerminated B. anthracis strain Ames spores. The macrophage-depleted mice were significantly more susceptible to the ensuing infection than the saline-pretreated mice, whereas the differences observed between the neutropenic mice and the saline-pretreated controls were generally not significant. We also found that augmenting peritoneal neutrophil populations before spore challenge did not increase resistance of the mice to infection. In addition, the bacterial load in macrophage-depleted mice was significantly greater and appeared significantly sooner than that observed with the saline-pretreated mice. However, the bacterial load in the neutropenic mice was comparable to that of the saline-pretreated mice. These data suggest that, in our model, neutrophils play a relatively minor role in the early host response to spores, whereas macrophages play a more dominant role in early host defenses against infection by B. anthracis spores.

Rechallenge of previously-infected pregnant ewes with Chlamydophila abortus

In an attempt to ascertain the means whereby previous exposure to Chlamydophila (C.) abortus can protect against the re-occurrence of enzootic abortion of ewes (EAE), ten previously-exposed ewes were intravenously rechallenged with a large infective dose of C. abortus during pregnancy. The patterns of development of chlamydial placentitis and its sequelae closely resembled that observed following first-time challenge of previously-naïve ewes, although placentitis appeared to develop more slowly following rechallenge infection and none of the rechallenged ewes aborted. Chorioallantoic and foetal pathology and foetal immune responses were qualitatively similar whilst the local maternal response to C. abortus infection of the endometrium did not appear to differ in rechallenged and first-time challenged sheep. This demonstrates that if C. abortus reaches the foetal side of the placenta, a stereotypical response is elicited, regardless of the status of maternal immunity. Therefore it appears that in natural circumstances, acquired immunity of the dam protects against the re-occurrence of EAE by preventing the causative agent from reaching the susceptible foetal trophoblast.

Neutrophil responses to Mycobacterium tuberculosis infection in genetically susceptible and resistant mice

The role of neutrophils in tuberculosis (TB) resistance and pathology is poorly understood. Neutrophil reactions are meant to target the offending pathogen but may lead to destruction of the host lung tissue, making the defending cells an enemy. Here, we show that mice of the I/St strain which are genetically susceptible to TB show an unusually high and prolonged neutrophil accumulation in their lungs after intratracheal infection. Compared to neutrophils from more resistant A/Sn mice, I/St neutrophils display an increased mobility and tissue influx, prolonged lifespan, low expression of the CD95 (Fas) apoptotic receptor, relative resistance to apoptosis, and an increased phagocytic capacity for mycobacteria. Segregation genetic analysis in (I/St x A/Sn)F2 hybrids indicates that the alleles of I/St origin at the chromosome 3 and 17 quantitative trait loci which are involved in the control of TB severity also determine a high level of neutrophil influx. These features, along with the poor ability of neutrophils to restrict mycobacterial growth compared to that of lung macrophages, indicate that the prevalence of neutrophils in TB inflammation contributes to the development of pathology, rather than protection of the host, and that neutrophils may play the role of a "Trojan horse" for mycobacteria.

Immunopathology of Chlamydophila abortus infection in sheep and mice

Chlamydophila abortus targets the placenta, causing tissue damage, inflammation and abortion (enzootic abortion of ewes). It is one of the main infectious causes of abortion in ewes, resulting in major economic losses to agricultural industries worldwide. Although ruminants and pigs are the principal hosts, humans are also susceptible to infection. Control of disease requires a host inflammatory response, which is likely to contribute to pathology and abortion. Mouse models have been widely used to provide insight into the role of specific immune cells in controlling infection and disease. The use of such model systems for investigating the mechanisms of abortion, latency, persistence, and immunity to reinfection will result in the identification of novel vaccine control strategies for sheep.

Genetic and pharmacological inhibition of poly(ADP-ribose) polymerase-1 interferes in the chlamydial life cycle

Chlamydiaceae are intracellular bacteria responsible for a variety of infections, ranging from asymptomatic to very severe, in humans and animals. We have investigated the role of poly(ADP-ribose) polymerase-1 (PARP-1) in Chlamydophila abortus infection using PARP-1-/- and their littermates PARP-1+/+ mice. Infection was resolved more efficiently by PARP-1-/- than PARP-1+/+ mice. However, the inflammatory response was similar in both strains, suggesting a potential role for PARP-1 in the cross-talk between this microorganism and the host cells. PARP-1-/- fibroblasts showed a 10-fold lower rate of chlamydiae production than PARP-1+/+. Moreover, a strong inhibition of bacterial production was also observed after pharmacological inhibition of PARP-1 activity in McCoy cells. Likewise, PARP-1 inhibition induced a higher level of cell death of infected cells, interfering in this way with the normal bacterial cell cycle. Overall, we identify PARP-1 as a new molecule involved in chlamydial developmental cycle, although the intrinsic mechanisms deserve further studies.

Successful elimination of memory-type CD8+ T cell subsets by the administration of anti-Gr-1 monoclonal antibody in vivo

During investigating the expression of Gr-1 antigen on various subsets of mouse spleen cells, we found that Gr-1 was expressed on memory-type CD8(+)CD44(high)CD62L(high) T cells in addition to granulocytes. Intraperitoneal administration of anti-Gr-1 mAb caused almost complete elimination of Ly-6C(+) memory-type CD8(+) T cells as well as Ly-6G(+) granulocytes. Anti-Gr-1 mAb-treated mouse spleen cells exhibited greatly reduced IFN-gamma production in response to anti-CD3 mAb both in vitro and in vivo. This reduced cytokine production appeared to be derived from elimination of IFN-gamma-producing Gr-1(+)CD8(+) T cells. Indeed, CD8(+) T cells with IFN-gamma-producing activity and cytotoxicity were generated from isolated Gr-1(+)CD8(+) cells but not from Gr-1(-)CD8(+) T cells. We also demonstrated that therapeutic effect of MBL-2 tumor-immunized spleen cells was greatly reduced by anti-Gr-1 mAb-treatment. Thus, we initially demonstrated that anti-Gr-1 mAb might become a good tool to investigate a precise role for memory-type CD8(+) T cells in vivo.

Collagen type II-specific monoclonal antibody-induced arthritis in mice: description of the disease and the influence of age, sex, and genes

Transfer of collagen type II (CII)-specific monoclonal antibodies induces an acute form of arthritis (collagen type II antibody-induced arthritis, CAIA) in naïve mice. Arthritis was induced using a pair of monoclonal antibodies M2139 and CIIC1, binding to J1 and C1(I) epitopes of CII, respectively. Thereafter, lipopolysaccharide injection was used to increase the incidence and severity of the disease. This model was used to investigate the effect of genes, age, and sex as well as effector cells in the end-stage effector phase of arthritis pathogenesis. Injection of a single monoclonal antibody induced arthritis only after lipopolysaccharide stimulation. CAIA showed differences in disease penetration among the susceptible strains indicating the importance of non-major histocompatibility complex genes on the antibody effector pathway. B-cell-deficient mice were susceptible to CAIA and in some genetic backgrounds B-cell deficiency leads to enhanced arthritis. Histology of the affected paws revealed massive infiltrations of neutrophils along with bone and cartilage erosion, pannus formation, and fibrin deposition. Depletion of neutrophils significantly reduced the incidence and severity of the disease. CAIA susceptibility increased with age. Males were more susceptible than females and estrogen treatment decreased the development of arthritis. We conclude that CAIA is an acute arthritis triggered by antibody binding and neutrophils bypassing immune activation but with many characteristics in common with collagen-induced arthritis.

Relationship between the immune response and protection conferred by new designed inactivated vaccines against ovine enzootic abortion in a mouse model

Chlamydophila abortus is a gram-negative obligate intracellular bacterium and the etiological agent of ovine enzootic abortion (OEA), an economically important disease in many countries. Inactivated vaccines have been reported to induce immunity in ewes and they have been used for many years. However, some outbreaks have been reported in correctly vaccinated flocks, so it is clear that new vaccines are necessary to address adequate protection and to avoid the shedding of the microorganism. This idea lead us to design inactivated vaccines, in a previously established mouse model, evaluating different inactivation procedures and new adjuvants. To assess the protection conferred, the results were analyzed on the basis of clinical signs and the isolation of C. abortus from spleen. These findings were correlated with the immune response induced by the vaccines, as determined by the production of C. abortus-specific IFN-gamma and IL-4 from splenocyte cultures and the detection of IgG isotypes in serum. BEI was found to be the best C. abortus-inactivation procedure. The inactivated vaccines adjuvated with QS-21 (QS) or Montanide 773 (M7) induced the best protection both against homologous and heterologous challenge, with an adequate (Th1-like) immune response. Finally, these selected vaccines were evaluated in a pregnant mouse model, in which they were seen to confer good protection and to avoid the C. abortus persistence in uterus after delivery. With these results, this mouse model could be considered as an adequate tool for selecting and optimizing effective vaccines against OEA.

B-cell-deficient mice show an exacerbated inflammatory response in a model of Chlamydophila abortus infection

The resolution of Chlamydophila abortus (Chlamydia psittaci serotype 1) infection is dependent on gamma interferon and CD8(+) T cells, and classically, B cells have been considered to play a minimal role in host defense. The role of B cells in the immune response was studied by using a model of infection in mice with genetically modified immunoglobulin M transmembrane domains ( micro MT). In the absence of B cells, infection with C. abortus leads to an acute severe fatal disease that involves a disseminated intravascular coagulation syndrome. micro MT mice displayed an increased level of proinflammatory cytokines in serum, and an increased number of neutrophils was observed in the lesions. The possible deleterious role of neutrophils in the pathogenesis of disease in micro MT mice was determined by depletion of the neutrophils with the monoclonal antibody RB6-8C5. This led to an enhancement of the bacterial burden and early mortality in both micro MT and wild-type mice, while necrotic lesions remained. Analysis of the presence of immunoregulatory cytokines showed significantly lower levels of transforming growth factor beta in the sera of micro MT mice. However, mice lacking mature B cells were able to establish a specific immune response that protected them from a secondary challenge. Taken together, these data suggest an immunomodulatory role for B cells in the early events of C. abortus primary infection that can protect mice against an exaggerated inflammatory response.

Neutropenia augments experimentally induced Schistosoma japonicum egg granuloma formation in CBA mice, but not in C57BL/6 mice

The present study was designed to investigate the role of neutrophils during the development of Schistosoma japonicum egg granulomas, in C57BL/6 and CBA mice. Laid eggs were implanted into the liver and monoclonal antibody, RB6-8C5, was used to eliminate neutrophils. After daily antibody treatment between days 9 and 13 of egg implantation, both strains of mice showed a marked decrease in neutrophil infiltration and coagulative hepatocyte necrosis at 2 weeks. At 4 weeks, after antibody administration every other day between days 16 and 26, granuloma formation in C57BL/6 mice was not affected by the treatment, whereas CBA mice exhibited a significant increase of reactions. Neutropenia augmented the Th2 cytokine response (IL-4, IL-13 and IL-5), but not for IFN-gamma at any time point examined and in either strain of mice. Higher levels of IL-4 and IL-13 were noted in CBA mice at early and late stages of granuloma formation, compared to C57BL/6 mice. There was also a striking difference in IL-13 production between the two strains. Our results indicate that neutropenia is associated with a significant augmentation of S. japonicum egg-induced granuloma formation in CBA mice, probably through increase in Th2 cytokines, however, the effects differ between early and late stages and between high and low responders.

Previous infection with the nematode Nippostrongylus brasiliensis alters the immune specific response against Chlamydophila abortus infection

An experimental mouse model to analyze the interaction between the immune responses elicited following infection with Nippostrongylus brasiliensis and Chlamydophila abortus has been established. Mice infected with C. abortus 7 days after N. brasiliensis showed an increased bacterial multiplication in spleen and liver compared to bacteria-alone infected mice. However the morbidity of these mice, expressed as weight loss, was significantly lower. Analysis of the immune responses elicited showed that spleen from co-infected mice had reduced IFN-gamma production in response to C. abortus antigen. The bias towards a type 2 response in co-infected mice was confirmed by an increase in the production of IL-4 and in the lower ratio IgG2a/IgG1. In pregnant mice co-infection caused a delay in the time of abortion and an increased systemic susceptibility to C. abortus infection.

Increased expression of the chemokine receptor CXCR3 and its ligand CXCL10 in peripheral airways of smokers with chronic obstructive pulmonary disease

CXCR3 is a chemokine receptor preferentially expressed on lymphocytes, particularly on type-1 T-lymphocytes. Smokers who develop chronic obstructive pulmonary disease (COPD) have a chronic bronchopulmonary inflammation that is characterized by an increased infiltration of T-lymphocytes, particularly CD8(+), in the airways and lung parenchyma. To investigate the expression of CXCR3 and its ligand interferon-induced protein 10/CXCL10 in COPD, we counted the number of CXCR3(+) cells and analyzed the expression of CXCL10 in the peripheral airways of 19 patients undergoing lung resection for localized pulmonary lesions. We examined lung specimens from seven smokers with fixed airflow limitation (COPD), five smokers with normal lung function, and seven nonsmoking subjects with normal lung function. The number of CXCR3(+) cells was immunohistochemically quantified in the epithelium, in the submucosa, and in the adventitia of peripheral airways. The number of CXCR3(+) cells in the epithelium and submucosa was increased in smokers with COPD as compared with nonsmoking subjects, but not as compared with smokers with normal lung function. Immunoreactivity for the CXCR3-ligand CXCL10 was present in the bronchiolar epithelium of smokers with COPD but not in the bronchiolar epithelium of smoking and nonsmoking control subjects. Most CXCR3(+) cells coexpressed CD8 and produced interferon gamma. These findings suggest that the CXCR3/CXCL10 axis may be involved in the T cell recruitment that occurs in peripheral airways of smokers with COPD and that these T cells may have a type-1 profile.

In vivo involvement of polymorphonuclear neutrophils in Leishmania infantum infection

BACKGROUND

The role of lymphocytes in the specific defence against L. infantum has been well established, but the part played by polynuclear neutrophil (PN) cells in controlling visceral leishmaniasis was much less studied. In this report we examine in vivo the participation of PN in early and late phases of infection by L. infantum.

RESULTS

Promastigote phagocytosis and killing occurs very early after infection, as demonstrated by electron microscopy analyses which show in BALB/c mouse spleen, but not in liver, numerous PN harbouring ultrastructurally degraded parasites. It is shown, using mAb RB6-8C5 directed against mature mouse granulocytes, that in chronically infected mice, long-term PN depletion did not enhance parasite counts neither in liver nor in spleen, indicating that these cells are not involved in the late phase of L. infantum infection. In acute stage of infection, in mouse liver, where L. infantum load is initially larger than that in spleen but resolves spontaneously, there was no significant effect of neutrophils depletion. By contrast, early in infection the neutrophil cells crucially contributed to parasite killing in spleen, since PN depletion, performed before and up to 7 days after the parasite inoculation, resulted in a ten-fold increase of parasite burden.

CONCLUSIONS

Taken together these data show that neutrophil cells contribute to the early control of the parasite growth in spleen but not in liver and that these cells have no significant effect late in infection in either of these target organs.

Endogenous interleukin-12 is not required for resolution of Chlamydophila abortus (Chlamydia psittaci serotype 1) infection in mice

A Th1 immune response involving gamma interferon (IFN-gamma) production is required to eliminate Chlamydophila abortus infections. In this study, the role of interleukin-12 (IL-12) in protecting against C. abortus infection was investigated using IL-12(-/-) and wild-type (WT) C57BL/6 mice to determine the role of this Th1-promoting cytokine. IL-12(-/-) mice were able to eliminate the C. abortus infection in a primary infection. However, there was a delay in the clearance of bacteria when IL-12(-/-) mice were infected with a sublethal dose of C. abortus, the delay being associated with a lower production of IFN-gamma. The low level of IFN-gamma was essential for survival of IL-12(-/-) infected mice. Both WT and IL-12(-/-) mice developed a Th1 immune response against C. abortus infection, since they both produced IFN-gamma and immunoglobulin G2a antibody isotype. In addition, when mice were given a secondary infectious challenge with C. abortus, a protective host response which resolved the secondary infection was developed by both WT and IL-12(-/-) mice. The lack of IL-12 resulted in few infiltrating CD4(+) T cells in the liver relative to the number in WT mice, although the number of CD8(+) T cells was slightly higher. The more intense Th1 response presented by WT mice may have a pathogenic effect, as the animals showed higher morbidity after the infection. In conclusion, these results suggest that although IL-12 expedites the clearance of C. abortus infection, this cytokine is not essential for the establishment of a protective host response against the infection.

Essential role of neutrophils in the initiation and progression of a murine model of rheumatoid arthritis

Neutrophils are prominent participants in the joint inflammation of human rheumatoid arthritis (RA) patients, but the extent of their role in the inductive phase of joint inflammation is unknown. In the K/BxN mouse RA model, transfer of autoreactive Ig from the K/BxN mouse into mice induces a rapid and profound joint-specific inflammatory response reminiscent of human RA. We observed that after K/BxN serum transfer, the earliest clinical signs of inflammation in the ankle joint correlated with the presence of neutrophils in the synovial regions of recipient mouse ankle joints. In this study, we investigated the role of neutrophils in the early inflammatory response to transferred arthritogenic serum from the K/BxN transgenic mouse. Mice were treated with a neutrophil-depleting mAb before and following transfer of arthritogenic serum and scored for clinical indications of inflammation and severity of swelling in ankle joints and front paws. In the absence of neutrophils, mice were completely resistant to the inflammatory effects of K/BxN serum. Importantly, depletion of neutrophils in diseased recipient mice up to 5 days after serum transfer reversed the inflammatory reaction in the joints. Transfer of serum into mice deficient in the generation of nitrogen or oxygen radicals (inducible NO synthase 2 or gp91(phox) genes, respectively) gave normal inflammatory responses, indicating that neither pathway is essential for disease induction. These studies have identified a critical role for neutrophils in initiating and maintaining inflammatory processes in the joint.

Neutrophil depletion during Toxoplasma gondii infection leads to impaired immunity and lethal systemic pathology

The immunomodulatory role of neutrophils during infection with Toxoplasma gondii was investigated. Monoclonal antibody-mediated depletion revealed that neutrophils are essential for survival during the first few days of infection. Moreover, neutrophil depletion was associated with a weaker type 1 immune response as measured by decreased levels of gamma interferon, interleukin-12 (IL-12) and tumor necrosis factor alpha. IL-10 was also decreased in depleted animals. Additionally, splenic populations of CD4(+) T cells, CD8(+) T cells, and NK1.1(+) cells were decreased in depleted mice. Neutrophil-depleted mice exhibited lesions of greater severity in tissues examined and a greater parasite burden as determined by histopathology and reverse transcription-PCR. We conclude that neutrophils are critical near the time of infection because they influence the character of the immune response and control tachyzoite replication.

Limited role of polymorphonuclear neutrophils in a pregnant mouse model of secondary infection by Chlamydophila abortus (Chlamydia psittaci serotype 1)

The aim of this work was to study the role of polymorphonuclear neutrophils (PMNs) in the clearance of infection, and in the development of specific immunity against Chlamydophila abortus (Chlamydia psittaci serotype 1) secondary infection. A pregnant mouse model depleted of neutrophils by the RB6-8C5 monoclonal antibody was used. No clinical signs were observed in depleted or non-depleted mice after secondary infection and no significant differences were observed in the litter size between the infected and control groups. In PMN-depleted mice C. abortus was not detected in the materno-fetal unit but merely produced low, persistent levels of infection in spleen and liver. In the non-depleted mice the level of infection was significantly lower, being resolved during the first few days post-reinfection. In both infected mice groups the immune response in the liver was quickly established and was seen to be composed mainly of CD4(+)T lymphocytes and macrophages. A Th1 response characterized by the presence of IFN-gamma and TNF-alpha in serum was observed during early infection, with significantly higher levels in the non-depleted animals. Our results suggest that PMNs have little influence on the control of C. abortus secondary infection, although they are a first line of defense and may influence the early production of TNF-alpha and IFN-gamma.

Chlamydophila abortus (Chlamydia psittaci serotype 1) clearance is associated with the early recruitment of neutrophils and CD8(+)T cells in a mouse model

The immune mechanisms in response to Chlamydophila abortus (Chlamydia psittaci serotype 1) infection were studied in C57BL/6 and CBA mice. The infection was monitored and the following aspects of the immune response were evaluated: the nature of the leucocyte infiltrate in the liver, the percentages of polymorphonuclear neutrophils (PMNs), macrophages and lymphocytes in the spleen, and the concentrations of cytokines in serum. In addition, the serum concentrations of IgG1 and IgG2a were determined. Both mouse strains showed a Th1-like immune response, with high concentrations of IFN-gamma and minimal levels of IL-4; however, C57 mice differed from CBA mice in showing milder clinical signs and earlier resolution of infection. The greater ability of C57 mice than CBA mice to eliminate chlamydophilae was related to the establishment of an earlier innate immunity, based on a more pronounced PMN response, and on a greater presence of CD8(+)T cells.