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

Chlamydia and Its Many Ways of Escaping the Host Immune System

The increasing number of new cases of Chlamydia infection worldwide may be attributed to the pathogen's ability to evade various host immune responses. Summarized here are means of evasion utilized by Chlamydia enabling survival in a hostile host environment. The pathogen's persistence involves a myriad of molecular interactions manifested in a variety of ways, e.g., formation of membranous intracytoplasmic inclusions and cytokine-induced amino acid synthesis, paralysis of phagocytic neutrophils, evasion of phagocytosis, inhibition of host cell apoptosis, suppression of antigen presentation, and induced expression of a check point inhibitor of programmed host cell death. Future studies could focus on the targeting of these molecules associated with immune evasion, thus limiting the spread and tissue damage caused by this pathogen.

Essential role for neutrophils in pathogenesis and adaptive immunity in Chlamydia caviae ocular infections

Trachoma, the world's leading cause of preventable blindness, is produced by chronic ocular infection with Chlamydia trachomatis, an obligate intracellular bacterium. While many studies have focused on immune mechanisms for trachoma during chronic stages of infection, less research has targeted immune mechanisms in primary ocular infections, events that could impact chronic responses. The goal of this study was to investigate the function of neutrophils during primary chlamydial ocular infection by using the guinea pig model of Chlamydia caviae inclusion conjunctivitis. We hypothesized that neutrophils help modulate the adaptive response and promote host tissue damage. To test these hypotheses, guinea pigs with primary C. caviae ocular infections were depleted of neutrophils by using rabbit antineutrophil antiserum, and immune responses and immunopathology were evaluated during the first 7 days of infection. Results showed that neutrophil depletion dramatically decreased ocular pathology, both clinically and histologically. The adaptive response was also altered, with increased C. caviae-specific IgA titers in tears and serum and decreased numbers of CD4(+) and CD8(+) T cells in infected conjunctivae. Additionally, there were changes in conjunctival chemokines and cytokines, such as increased expression of IgA-promoting interleukin-5 and anti-inflammatory transforming growth factor β, along with decreased expression of T cell-recruiting CCL5 (RANTES). This study, the first to investigate the role of neutrophils in primary chlamydial ocular infection, indicates a previously unappreciated role for neutrophils in modulating the adaptive response and suggests a prominent role for neutrophils in chlamydia-associated ocular pathology.

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.

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.

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.

Essential Role for Neutrophil Recruitment to the Liver in Concanavalin A-Induced Hepatitis

Leukocyte infiltration into the liver is paramount to the development of liver injury in hepatitis. Hepatitis occurring after the administration of Con A in mice is felt to be a T lymphocyte-mediated disease. In this study, we report that neutrophils are the key initiators of lymphocyte recruitment and liver injury caused by Con A. The objectives of this study were to investigate the involvement of neutrophils in Con A-induced hepatitis in vivo via intravital microscopy. After Con A administration, we observed a significant increase in leukocyte rolling flux, a decrease in rolling velocity, and an increase in leukocyte adhesion to the hepatic microvasculature. Fluorescence microscopy identified that within 4 h of Con A administration only a minority of the recruited leukocytes were T lymphocytes. Furthermore, immunohistochemistry showed a significant increase in neutrophils recruited to the liver post-Con A treatment in association with liver cell damage, as reflected by elevated serum alanine aminotransferase levels. Using flow cytometry, we observed that Con A could bind directly to neutrophils, which resulted in a shedding of L-selectin, an increase in beta(2)-integrin expression, and the production of reactive oxidants. Following neutrophil depletion, a significant inhibition of Con A-induced CD4+ T lymphocyte recruitment to the liver resulted and complete reduction in hepatic injury, as assessed by serum alanine aminotransferase levels. In summary, the present data support the concept that neutrophils play an important and previously unrecognized role in governing Con A-induced CD4+ T cell recruitment to the liver and the subsequent development of hepatitis.

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.