Richard P. Morrison

Chlamydial Heat Shock Protein 60 Activates Macrophages and Endothelial Cells Through Toll-Like Receptor 4 and MD2 in a MyD88-Dependent Pathway

Active inflammation and NF-κB activation contribute fundamentally to atherogenesis and plaque disruption. Accumulating evidence has implicated specific infectious agents including Chlamydia pneumoniae in the progression of atherogenesis. Chlamydial heat shock protein 60 (cHSP60) has been implicated in the induction of deleterious immune responses in human chlamydial infections and has been found to colocalize with infiltrating macrophages in atheroma lesions. cHSP60 might stimulate, enhance, and maintain innate immune and inflammatory responses and contribute to atherogenesis. In this study, we investigated the signaling mechanism of cHSP60. Recombinant cHSP60 rapidly activated NF-κB in human microvascular endothelial cells (EC) and in mouse macrophages, and induced human IL-8 promoter activity in EC. The inflammatory effect of cHSP60 was heat labile, thus excluding a role of contaminating LPS, and was blocked by specific anti-chlamydial HSP60 mAb. In human vascular EC which express Toll-like receptor 4 (TLR4) mRNA and protein, nonsignaling TLR4 constructs that act as dominant negative blocked cHSP60-mediated NF-κB activation. Furthermore, an anti-TLR4 Ab abolished cHSP60-induced cellular activation, whereas a control Ab had no effect. In 293 cells, cHSP60-mediated NF-κB activation required both TLR4 and MD2. A dominant-negative MyD88 construct also inhibited cHSP60-induced NF-κB activation. Collectively, our results indicate that cHSP60 is a potent inducer of vascular EC and macrophage inflammatory responses, which are very relevant to atherogenesis. The inflammatory effects are mediated through the innate immune receptor complex TLR4-MD2 and proceeds via the MyD88-dependent signaling pathway. These findings may help elucidate the mechanisms by which chronic asymptomatic chlamydial infection contribute to atherogenesis.

Immunity to Murine Chlamydial Genital Infection

Chlamydia trachomatis sexually transmitted infections cause considerable morbidity and socioeconomic burden worldwide, despite significant advances in our understanding of the biology (29, 31, 57), pathogenesis (11, 83, 117), genomics (94), and epidemiology (91) of this parasite. Chlamydial urogenital tract infections are readily cured with antibiotics, but control measures based on antimicrobial chemotherapy alone are hampered by the frequency of asymptomatic infections and delayed diagnosis (9). Definitive control of C. trachomatis sexually transmitted diseases (STDs) is possible through the development of a safe and efficacious vaccine (24). Progress toward the development of an effective vaccine has been disappointingly modest, as it has been for vaccines to other sexually transmitted pathogens that infect the genital tract mucosae. The strict tropism for mucosal epithelial cells, the complex biology and antigenic structure, and the predilection to cause persistent infection have presented formidable challenges to chlamydial vaccine development. A heightened understanding of protective immunity to C. trachomatis urogenital infection has emerged in the past decade from studies using a mouse model of chlamydial genital tract infection. The insights are of considerable interest because they offer promise for the development of an efficacious chlamydial vaccine. This review focuses on that progress and summarizes the current understanding of protective immune mechanisms that function against murine chlamydial urogenital infection. We also discuss specific requirements for a vaccine to protect against chlamydial STDs and the challenges presently confronting us in achieving that goal.

Immunity to Murine Chlamydia trachomatis Genital Tract Reinfection Involves B Cells and CD4+ T Cells but Not CD8+ T Cells

ABSTRACT CD4+ T-helper type 1 (Th1) responses are essential for the resolution of a primary Chlamydia trachomatis genital tract infection; however, elements of the immune response that function in resistance to reinfection are poorly understood. Defining the mechanisms of immune resistance to reinfection is important because the elements of protective adaptive immunity are distinguished by immunological memory and high-affinity antigen recognition, both of which are crucial to the development of efficacious vaccines. Using in vivo antibody depletion of CD4+ and CD8+ T cells prior to secondary intravaginal challenge, we identified lymphocyte populations that functioned in resistance to secondary chlamydial infection of the genital tract. Depletion of either CD4+ or CD8+ T cells in immune wild-type C57BL/6 mice had a limited effect on resistance to reinfection. However, depletion of CD4+ T cells, but not CD8+ T cells, in immune B-cell-deficient mice profoundly altered the course of secondary infection. CD4-depleted B-cell-deficient mice were unable to resolve a secondary infection, shed high levels of infectious chlamydiae, and did not resolve the infection until 3 to 4 weeks following the discontinuation of anti-CD4 treatment. These findings substantiated a predominant role for CD4+ T cells in host resistance to chlamydial reinfection of the female genital tract and demonstrated that CD8+ T cells are unnecessary for adaptive immune resistance. More importantly, however, this study establishes a previously unrecognized but very significant role for B cells in resistance to chlamydial reinfection and suggests that B cells and CD4+ T cells may function synergistically in providing immunity in this model of chlamydial infection. Whether CD4+ T cells and B cells function independently or dependently is unknown, but definition of those mechanisms is fundamental to understanding optimum protective immunity and to the development of highly efficacious immunotherapies against chlamydial urogenital infections.

Cellular Oxidation of Low-Density Lipoprotein by Chlamydia pneumoniae

A spectrum of clinical and epidemiologic studies implicate infectious agents, including Chlamydia pneumoniae, in the pathogenesis of atherosclerosis. The complexity of atherosclerotic disease necessitates examining the role of infection in the context of defined risk factors, such as high levels of native low-density lipoprotein (LDL). Although native LDL does not have atherogenic properties, cellular oxidation of LDL alters the lipoprotein into a highly atherogenic form. In this report, C. pneumoniae and chlamydial hsp60, an inflammatory antigen that was recently localized to atheromas, were found to induce cellular oxidation of LDL. These data provide initial evidence that an infectious agent can render LDL atherogenic and suggest a mechanism whereby C. pneumoniae may promote atheroma development.

Cross-Reactive B-Cell Epitopes of Microbial and Human Heat Shock Protein 60/65 in Atherosclerosis

Objective—Growing evidence suggests that immune reactions to heat shock protein 60 (HSP60) are involved in atherogenesis. Because of the high phylogenetic conservation between microbial and human HSP60, bacterial infections might be responsible for breaking the tolerance to self-HSP60, which is expressed on the surface of stressed arterial endothelial cells. Methods and Results—We purified serum antibodies to Escherichia coli HSP60 (GroEL), the 60-kD chlamydial HSP, and HSP65 of Mycobacterium tuberculosis by affinity chromatography from clinically healthy subjects with sonographically proven carotid atherosclerosis. Reactivity of the purified antibodies with overlapping human HSP60 peptides was measured, and 8 shared common epitopes, recognized by all anti-bacterial HSP60/65 antibodies, were identified. Antisera specific for these cross-reactive epitopes were produced by immunizing rabbits with peptides derived from human HSP60. By immunohistochemistry, the epitopes were found to be present in the arterial wall of young subjects during the earliest stages of the disease. Conclusions—Antibodies to microbial HSP60/65 recognize specific epitopes on human HSP60. These cross-reactive epitopes were shown to serve as autoimmune targets in incipient atherosclerosis and might provide further insights into the mechanisms of early atherogenesis.

Detection of Chlamydia pneumoniae–Reactive T Lymphocytes in Human Atherosclerotic Plaques of Carotid Artery

Linkage between Chlamydia pneumoniae infection and atherosclerosis has been confirmed in several studies, but the precise role of this organism in the disease process is not known. We investigated the relation and reactivity of T lymphocytes of human carotid plaques to C pneumoniae antigens. Tissue specimens were obtained from 17 patients who underwent carotid endarterectomy. Immunohistological staining and/or in situ hybridization revealed the presence of C pneumoniae in 11 (64%) of the 17 of the cases. Inflammatory infiltration seen in the vessel walls consisted primarily of CD45RO+ T-memory lymphocytes (median 80%, range 50% to 90%), whereas CD20+ B cells and monocytes were in minor proportion. In vivo activated T lymphocytes were propagated from the specimens with interleukin-2, and the antigen specificity of the established T-cell lines (TLLs) was analyzed against C pneumoniae elementary body antigen. TLLs were established from all 17 carotid tissues but none from the control specimens of ascending aorta. C pneumoniae was recognized as a specific T-cell-stimulating antigen in 7 (41%) of 17 cases. Further analyses of the C pneumoniae-reactive TLLs showed that chlamydial 60-kDa heat-shock protein induced specific proliferation in 5 (71%) of 7 cases and revealed 2 haplotype (DRB1*1502 and DQB1*06) binding motifs in human 60-kDa heat-shock protein. C pneumoniae was identified as a specific microbial antigen recognized by 41% of TLLs propagated from in vivo activated plaque T cells. Our results suggests that cell-mediated immunity to C pneumoniae plays a role in the atherosclerotic process and that this response may involve autoimmunity.

Chlamydial virulence determinants in atherogenesis : The role of chlamydial lipopolysaccharide and heat shock protein 60 in macrophage-lipoprotein interactions

Data from a spectrum of epidemiologic, pathologic, and animal model studies show that Chlamydia pneumoniae infection is associated with coronary artery disease, but it is not clear how the organism may initiate or promote atherosclerosis. It is postulated that C. pneumoniae triggers key atherogenic events through specific virulence determinants. C. pneumoniae induces mononuclear phagocyte foam cell formation by chlamydial lipopolysaccharide (cLPS) and low-density lipoprotein oxidation by chlamydial hsp60 (chsp60). Thus, different chlamydial components may promote distinct events implicated in the development of atherosclerosis. Data implicating cLPS and chsp60 in the pathogenesis of atherosclerosis are discussed and novel approaches are presented for attempting to elucidate how these putative virulence determinants signal mononuclear phagocytes to modulate lipoprotein influx and modification.

Resolution of Secondary Chlamydia trachomatis Genital Tract Infection in Immune Mice with Depletion of Both CD4+ and CD8+ T cells

ABSTRACT The essential role of T cells in the resolution of primary murineChlamydia trachomatis genital tract infection is inarguable; however, much less is known about the mechanisms that confer resistance to reinfection. We previously established that CD4+ T cells and B cells contribute importantly to resistance to reinfection. In our current studies, we demonstrate that immune mice concurrently depleted of both CD4+ T cells and CD8+ T cells resisted reinfection as well as immunocompetent wild-type mice. The in vivo depletion of CD4+ and CD8+ T cells resulted in diminished chlamydia-specific delayed-type hypersensitivity responses, but antichlamydial antibody responses were unaffected. Our data indicate that immunity to chlamydial genital tract reinfection does not rely solely upon immune CD4+ or CD8+ T cells and further substantiate a predominant role for additional effector immune responses, such as B cells, in resistance to chlamydial genital tract reinfection.

In Situ Analysis of the Evolution of the Primary Immune Response in Murine Chlamydia trachomatis Genital Tract Infection

ABSTRACT Adaptive immune responses contribute to the resolution ofChlamydia trachomatis genital tract infection and protect against reinfection, but our understanding of the mechanisms of those protective responses is incomplete. In this study, we analyzed by in situ immunohistochemistry the progression of the inflammatory and cytokine responses in the genital tracts of mice vaginally infected with C. trachomatis strain mouse pneumonitis. The cellular inflammatory response was characterized by an initial elevation in myeloid cells in the vagina (day 3) and uterine horns (day 7), followed by a marked rise in the number of T cells, predominantly CD4+ cells. CD8+ T cells and CD45R+B cells were also detected but were much less numerous. Perivascular clusters of CD4+ T cells, which resembled clusters of T cells seen in delayed-type hypersensitivity responses, were evident by 2 weeks postinfection. Following the resolution of infection, few CD8+ T cells and CD45R+ B cells remained, whereas numerous CD4+ T cells and perivascular clusters of CD4+ T cells persisted in genital tract tissues. Interleukin-12 (IL-12)- and tumor necrosis factor alpha (TNF-α)-producing cells were observed in vaginal tissue by day 3 of infection and in uterine tissues by day 7. Cells producing IL-4 or IL-10 were absent from vaginal tissues at day 3 of infection but were present in uterine tissues by day 7 and were consistently more numerous than IL-12- and TNF-α-producing cells. Thus, the evolution of the local inflammatory response was characterized by the accumulation of CD4+ T cells into perivascular clusters and the presence of cells secreting both Th1- and Th2-type cytokines. The persistence of CD4+-T-cell clusters long after infection had resolved (day 70) may provide for a readily mobilizable T-cell response by which previously infected animals can quickly respond to and control a secondary infectious challenge.

The Effect of Doxycycline Treatment on the Development of Protective Immunity in a Murine Model of Chlamydial Genital Infection

Chlamydia trachomatis is a major cause of sexually transmitted disease (STD) worldwide. Antibiotics are effective in treating infection; however, reinfection is common. This observation has led to the conclusion that infection fails to elicit a protective antichlamydial immune response. It was postulated that high reinfection rates might be due to early eradication of organisms from genital tissue after antibiotic intervention, which could negatively influence the development of naturally acquired protective immunity. This hypothesis was tested by use of a murine model of female genital infection. The findings show that doxycycline intervention of infection, although very effective in eradicating chlamydiae from genital tissue and preventing upper genital tract disease, significantly inhibits the development of protective immunity. If antibiotic intervention of human chlamydial genital infection has a similar effect on protective immunity, it could have important implications in the understanding of immunity to infection and future public health efforts to control chlamydial STD.