Chlamydia trachomatis is an obligate intracellular bacterium that infects the oculogenital mucosae. C. trachomatis infection of the eye causes trachoma, the leading cause of preventable blindness. Infections of the genital mucosae are a leading cause of sexually transmitted diseases. A vaccine to prevent chlamydial infection is needed but has proven difficult to produce by using conventional vaccination approaches. Potent immunity to vaginal rechallenge in a murine model of chlamydial genital infection has been achieved only by infection or by immunization with dendritic cells (DC) pulsed ex vivo with whole inactivated organisms. Immunity generated by infection or ex vivo antigen-pulsed DC correlates with a chlamydia-specific interleukin 12 (IL-12)-dependent CD4 ؉ Th1 immune response. Because of the potent antichlamydial immunizing properties of DC, we hypothesized that DC could be a powerful vehicle for the delivery of individual chlamydial antigens that are thought to be targets for more conventional vaccine approaches. Here, we investigated the recombinant chlamydial major outer membrane protein (rMOMP) as a target antigen. The results demonstrate that DC pulsed with rMOMP secrete IL-12 and stimulate infection-sensitized CD4 ؉ T cells to proliferate and secrete gamma interferon. These immunological properties implied that rMOMP-pulsed DC would be potent inducers of MOMP-specific CD4 ؉ Th1 immunity in vivo; however, we observed the opposite result. DC pulsed ex vivo with rMOMP and adoptively transferred to naive mice generated a Th2 rather than a Th1 anti-MOMP immune response, and immunized mice were not protected following infectious challenge. We conclude from these studies that the immunological properties of ex vivo pulsed DC are not necessarily predictive of the immune response generated in vivo following adoptive transfer. These findings suggest that the nature of the antigen used to pulse DC ex vivo influences the Th1-Th2 balance of the immune response in vivo.

Chlamydia pneumoniae is an obligate intracellular pathogen that causes respiratory infections and has been associated with cardiovascular disease. We compared respiratory and cardiovascular isolates to find genetic differences associated with pathogenicity. A polymorphic region encoding a tyrosine/tryptophan permease was found to differ between disease isolates. Respiratory strains contained multiple copies of the tyrP gene, and vascular strains contained a single copy. Single-nucleotide polymorphism analysis revealed the duplication to be a phylogenetically old event. Gene amplification was associated with higher mRNA levels and higher uptake of the substrate tyrosine, indicating an amino-acid transport-related phenotype associated with the tyrP genotype. Vascular strains, despite their reduced ability to transport tyrosine, do not appear to have a reduced growth rate in vitro. We hypothesize that the important difference between strains of vascular and respiratory origin may lie in the increased tendency of vascular strains to elicit persistent infection that is triggered by amino-acid starvation.

We studied the expression of cytokines, chemokines, and chemokine receptors by the RNase protection assay in chlamydia-pulsed dendritic cells to better understand their potent anti-chlamydial immunizing properties. We found that chlamydia-pulsed dendritic cells express a complex profile of inflammatory and immunomodulatory molecules. These include CCR-7, interleukin-12, and interferon-induced protein 10, molecules that might influence the homing of pulsed dendritic cells to the site of chlamydial infection and the induction of a local protective CD4 ؉ Th1 cellular immunity.Chlamydia trachomatis is an obligatory intracellular bacterial parasite that infects the oculogenital mucosal epithelium, causing trachoma, the world's leading cause of preventable blindness, and sexually transmitted diseases. Pelvic inflammatory disease is a serious sequalae of C. trachomatis infection of the female genital tract that can result in tubal blockage, infertility, or ectopic pregnancy (2,4,8,13). The development of an efficacious vaccine against C. trachomatis oculogenital infection is likely to be key to the control of both trachoma and chlamydial sexually transmitted diseases. Despite considerable effort, however, there has been little favorable progress toward this end. Conventional vaccination approaches have produced disappointing results in their abilities to prevent infection of the mouse female genital tract (12,14,19), despite a modicum of success in controlling chlamydial infection of the respiratory tract (20). Solid protective immunity to genital rechallenge has been achieved only by infection or adoptive immunization with dendritic cells (DC) pulsed ex vivo with inactivated whole chlamydial organisms (6, 18). Interestingly, mice immunized with chlamydia-pulsed DC exhibit equivalent levels of protective immunity to that in mice that have spontaneously resolved a primary genital infection (18). Both infection-mediated protective immunity and immunity elicited following adoptive transfer of antigen-pulsed DC correlate with a chlamydia-specific CD4ϩ Th1-biased immune response characterized by the secretion of high levels of gamma interferon from local and splenic CD4ϩ T cells (6,18). Recent studies have also indicated an important cooperative role for both CD4 ϩ T cells and B cells in recall immunity in the murine model; however the mechanism(s) that mediates this cooperative effector function has not been described (11). Clearly, the use of ex vivo antigenpulsed DC as a practical chlamydial vaccine is unsuited for use in humans. Nevertheless, the ability of ex vivo antigen-pulsed DC to elicit solid antichlamydial protective immunity at the genital mucosae is gratifying because it demonstrates that a more complete understanding of chlamydia-DC interactions may provide important information applicable to the development of a conventional antichlamydial vaccine.In this work we have investigated cytokine, chemokine, and chemokine receptor gene expression in chlamydia-pulsed DC by the RNase protection assay (RPA). Our findin...