Chlamydia trachomatis infection: host immune responses and potential vaccines

Chlamydia trachomatis causes genital tract infections that affect men, women, and children on a global scale. This review focuses on innate and adaptive immune responses in the female reproductive tract (FRT) to genital tract infections with C. trachomatis. It covers C. trachomatis infections and highlights our current knowledge of genital tract infections, serovar distribution, infectious load, and clinical manifestations of these infections in women. The unique features of the immune system of the FRT will be discussed and will include a review of our current knowledge of innate and adaptive immunity to chlamydial infections at this mucosal site. The use of animal models to study the pathogenesis of, and immunity to, Chlamydia infection of the female genital tract will also be discussed and a review of recent immunization and challenge experiments in the murine model of chlamydial FRT infection will be presented.     

Role of gamma-delta T cells in murine Chlamydia trachomatis infection.

The role of gamma-delta T cells in host resistance to Chlamydia trachomatis was characterized by using a murine model of pneumonia caused by the mouse pneumonitis agent (MoPn), murine C. trachomatis. At days 3 and 7 after infection, gamma-delta T-cell-deficient knockout mice had significantly higher levels of MoPn in the lungs than did immunologically intact controls. At day 20, paradoxically, gamma-delta T-cell-deficient mice were more resistant to MoPn than were controls. This increased resistance was not due to an increased production of toxic cytokines or interleukin-10 in controls on that day. Gamma-delta T cells play a role in protection early in MoPn infection, but they may be deleterious later in infection, as has been observed in models of salmonella and trypanosome infection.     

Frequency of antigen-specific B cells during experimental ocular Chlamydia trachomatis infection.

Chlamydia-specific antibody-secreting cells have been identified in conjunctiva and draining cervical lymph nodes by an ELISPOT assay in a cynomolgus monkey model of trachoma. These local sites contained numbers of chlamydia-specific B cells that were higher than those in distant inguinal lymph nodes and peripheral blood. The numbers of chlamydia-specific immunoglobulin G-secreting B cells observed were 5 to 57 per 10(6) cells in conjunctiva and 24 to 996 per 10(6) cells in cervical lymph nodes during conjunctival infection or after challenge of immune monkeys with the chlamydial 57-kDa heat shock protein (hsp60). These studies demonstrate a large chlamydia-specific B-cell component in the conjunctiva during ocular chlamydial infection. These results are similar to our findings for chlamydia-specific T-cell responses.     

Growth of Chlamydia trachomatis in enucleated cells.

Chlamydia trachomatis is an obligate intracellular parasite of eucaryotic cells. Little is known about the role of the host in supporting chlamydial replication beyond the facts that host cells provide ATP and that de novo host protein synthesis is not required for bacterial growth. To further explore potential contributions of host nuclear function to chlamydial development, we questioned whether murine C. trachomatis could grow in mouse L cells that had been enucleated with cytochalasin B. Following enucleation, cells were infected with chlamydiae and analyzed morphologically and biochemically. Late in infection, substantial numbers of chlamydiae of all developmental stages were seen within large cytoplasmic inclusions that were indistinguishable from those seen in infected intact cells. Normal numbers of infectious progeny particles were produced from enucleated cultures. We conclude that active host cell nuclear function is not required to support the growth of chlamydiae.     

Growth of host cells and Chlamydia trachomatis in medium containing serum from 16-week-old calves.

We compared fetal bovine serum with five batches of serum from calves of various ages. HeLa and McCoy cells grown in only one batch of calf serum (from 16-week-old calves) had morphology, growth kinetics, and cloning efficiency similar to those of cells grown in fetal bovine serum. Cells maintained in calf serum from this batch supported the growth of two laboratory strains of Chlamydia trachomatis, a genital strain (E/UW-5/Cx) in McCoy cells and a lymphogranuloma venereum strain (440L) in HeLa cells. McCoy cells maintained in calf serum also supported the growth of C. trachomatis from clinical specimens. The batch of serum from 16-week-old calves was an effective alternative to fetal bovine serum for the growth of cells and of C. trachomatis. Other laboratories may be able to use calf serum for the maintenance of cells and for the isolation of Chlamydia spp. Before use, however, each batch of calf serum will have to be carefully evaluated to ensure that it is equivalent to fetal bovine serum.     

Reactivation of persistent Chlamydia trachomatis infection in cell culture.

Gamma interferon induces persistent chlamydial infections in cell culture. These infections are characterized by altered morphologic and biochemical features of the pathogen. These persistent forms are abnormally large and noninfectious and undergo unusual structural and functional changes, including production of a paucity of outer envelope constituents and normal levels of the chlamydial hsp60, an immunopathological antigen. The current investigation evaluates the events that occur during reactivation of infectious Chlamydia trachomatis from persistently infected cell cultures. Transfer of persistent chlamydial organisms to gamma interferon-free medium resulted in recovery of infectivity accompanied by an increase in levels of structural membrane proteins and reorganization of aberrant organisms to morphologically typical elementary bodies. In addition, reactivation of infectious organisms from persistent chlamydiae that were maintained in culture for several weeks was demonstrated. These studies show that persistent C. trachomatis maintains viability for extended periods, illustrate the reversibility of immunologically mediated persistent infections, and characterize reactivation at the ultrastructural and biochemical levels.     

Value of screening for oro-pharyngeal Chlamydia trachomatis infection.

AIMS--To determine whether oro-pharyngeal colonisation by Chlamydia trachomatis occurs in patients at risk of genital chlamydia infection; to determine whether screening pharyngeal specimens by polymerase chain reaction (PCR) increases detection of C trachomatis compared with isolation and the immune dot blot test; and to correlate the detection of C trachomatis and Neisseria gonorrhoeae in the pharynx with a history of oro-genital contact. METHODS--Thirteen homosexuals and 11 heterosexuals were included in the study. Urogenital and pharyngeal specimens were tested for C trachomatis and N gonorrhoeae using standard clinical diagnostic procedures. Two different PCR methodologies were also used to detect C trachomatis in the pharyngeal specimens. Results were correlated with the mode of sexual practice. RESULTS--Oro-genital sexual contact was practised by 64.9% (72/111) of heterosexuals in addition to penetrative penovaginal intercourse. Additionally, 62.1% (77/124) of all patients did not use any form of barrier protection. Of those who admitted to oro-genital sexual contact, 17.6% of patients with a genital chlamydial infection and 36.4% of those with genital gonorrhoea also had asymptomatic pharyngeal colonisation. C trachomatis was detected in three of 124 (2.4%) pharyngeal specimens by PCR which were reported as negative by chlamydial culture; one was positive by the immune dot blot test. CONCLUSION--The majority of patients practised unprotected oro-genital contact and significant pharyngeal colonisation by C trachomatis and N gonorrhoeae occurred if genital infection was present. Despite the use of PCR in a population at high risk of sexually transmitted disease, the prevalence of chlamydia in the pharynx was very low. This indicates that transmission of C trachomatis to the oro-pharynx does not pose a serious health risk and that screening of patients for oro-pharyngeal C trachomatis is not worthwhile.     

沙眼衣原体感染诱导精子凋亡

目的:研究精液沙眼衣原体(CT)感染对男性生殖的影响.方法:选择精液CT阳性的男性不育者57例作为CT阳性组,另选择正常对照组15例.检测精液常规,免疫层析法检测CT感染情况,末端脱氧核苷酸转移酶(TdT)介导的TUNEL法检测凋亡精子.结果: CT阳性组精子凋亡率为33.03%±14.98%,正常对照组为9.68%±2.78%,CT阳性组精子凋亡率明显增高.结论:精液CT感染诱导精子凋亡率增加,精液沙眼衣原体感染是引起男性不育的原因之一.     

Cultivation of Chlamydia trachomatis in cycloheximide-treated mccoy cells.

An isolation technique for Chlamydia trachomatis using McCoy cells is described. In contrast to earlier techniques employing such cells, no pretreatment of the cells was used. The glutarimide antibiotic cycloheximide was added to the culture medium used for incubating the cells after infection. Cycloheximide was used at concentrations that depressed, but did not completely inhibit, the metabolism of the eucaryotic host cells. In studies on different immunotypes of C. trachomatis cultured in the yolk sac of embryonated hen eggs, the cycloheximide technique was compared with a method using pretreatment of cells with 5-iodo-2-deoxyuridine. The cycloheximide method gave greater numbers of inclusion-forming units per cover slip for all the immunotypes of trachoma-inclusion conjunctivitis agents tested, i.e., A through I. In a study of 194 cervical and urethral specimens from women, cycloheximide treatment of McCoy cells was found to be more efficient than 5-iodo-2-deoxyuridine treatment for the isolation of C. trachomatis.     

Protegrins: structural requirements for inactivating elementary bodies of Chlamydia trachomatis.

We tested 20 protegrins against Chlamydia trachomatis serovar L2 (L2/434/Bu). Five of the protegrins had native structures; the others included nonamidated, enantiomeric, and truncated variants and peptides with <2 disulfide bonds. Antichlamydial activity resided principally in residues 5 to 15 of native protegrin PG-1, and optimal activity required both intramolecular disulfide bonds.     

Role of endogenous gamma interferon in host defense against Chlamydia trachomatis infections.

BALB/c mice (6 to 8 weeks old) infected with Chlamydia trachomatis serovar L1 were sacrificed, and the yield of Chlamydia inclusion-forming units from the liver and lungs was measured in HeLa 229 cells. The yield of inclusion-forming units reached a peak at 3 days postinfection and then progressively declined. The mice infected with C. trachomatis had no detectable levels of gamma interferon (IFN-gamma) in their sera. However, stimulation of their spleen cells with either concanavalin A or heat-killed C. trachomatis resulted in the release of high levels of IFN-gamma (600 to 900 IU/ml) at 5 to 8 days postinfection. The increased release of IFN-gamma from the spleen cells paralleled the clearance of chlamydia from the liver and lungs. Sera and spleen cells from animals immunized with live C. trachomatis were transferred to recipient mice that were subsequently challenged with C. trachomatis. Transfer of spleen cells resulted in a reduction of the infection in the recipient animal as measured by the yield of chlamydia from the spleen, but transfer of the sera did not confer protective immunity. In addition, mice infected with C. trachomatis serovar L1 were treated with a hamster neutralizing monoclonal antibody to recombinant murine IFN-gamma (MAb-MuIFN-gamma). In the animals receiving the MAb-MuIFN-gamma, the yield of chlamydia from the lungs, spleen, and liver was significantly higher than from the control groups of mice. Histopathological analysis of tissues from the chlamydia-infected mice showed that the animals treated with the MAb-MuIFN-gamma had a significantly more extensive inflammatory reaction in their lungs, liver, and spleen.     

Reactivation of Chlamydia trachomatis lung infection in mice by cortisone.

To study the latency, chronicity, and recurrent nature of chlamydial infection, we attempted to reactivate Chlamydia trachomatis lung infection in mice by immunosuppressive therapy with cortisone. Mice were treated with subcutaneous injections of cortisone acetate (125 mg/kg) every other day, starting on day 14 after intranasal inoculation of C. trachomatis serotype B (TW-5). C. trachomatis was recovered from the lungs beginning day 6 after the start of cortisone treatment until the end of the observation period on day 12 of treatment. Overall, the reactivation was successful in 8 of 55 mice treated with cortisone, in contrast to 0 of 41 inoculated, untreated mice (P = 0.009) and 0 of 35 uninoculated, treated mice. Cortisone treatment affected the ability of peritoneal exudate cells to respond to migratory inhibition after exposure to purified whole organisms of C. trachomatis serotype B (TW-5) but had little effect on serum antibody titers, indicating a possible role for cellular immunity in resistance against C. trachomatis infection in the lung.     

Characterization of host cell death induced by Chlamydia trachomatis

Chlamydia are obligate intracellular bacteria that modulate apoptosis of the host cell. Strikingly, chlamydial infection has been reported both to inhibit and to induce apoptosis. Although the ability to inhibit apoptosis has been corroborated by the identification of cellular targets, confirmation of cell death induction has been complicated by a mixture of apoptotic features and atypical cell death during infection, as well as by differences in the experimental techniques used to measure cell death. Here we use a panel of well-established approaches in the study of apoptosis to define the form of cell death induced by Chlamydia trachomatis infection. Infected cells displayed apoptotic features such as nuclear condensation and fragmentation, as well as positive TUNEL (terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling) staining. Fragmentation of genomic DNA occurred, but was atypical. Clear evidence against the activation of effector caspases was found. Nuclear changes were measured in fibroblasts lacking one or both of the effectors of mitochondrial apoptosis, Bax and Bak. A slight reduction in nuclear changes was observed in Bax-deficient cells and in Bax/Bak double-deficient cells. Most surprisingly, this reduction was almost complete in Bak-deficient cells. Finally, dying infected cells were efficiently taken up by professional phagocytes, suggesting that Chlamydia-induced host-cell death could play a role in the immune response. In conclusion, chlamydial infection can induce cell death. Although Chlamydia-induced cell death has certain morphological features of apoptosis, it does not result from activation of the apoptotic pathway.     

Amino acid requirements of a Chlamydia trachomatis genital strain in McCoy cell cultures.

Amino acid requirements of a Chlamydia trachomatis were defined in McCoy cell monolayer cultures, depleted of their nutrient reserves by maintenance in Earle balanced salt solution for at least 2 days, and then treated at infection with 1 microgram of cycloheximide per ml, an inhibitor of host cell protein and deoxyribonucleic acid synthesis. Serum-free Waymouth MB 752/1 medium lacking one amino acid or a group of related amino acids was added to depleted cultures before infection. Eight of the amino acids normally present in MB 752/1 were essential for chlamydial growth, six were advantageous for growth, and five were nonessential.     

Plasma cell endometritis is associated with Chlamydia trachomatis infection.

The presence of plasma cells in endometrial tissue has been linked to Chlamydia trachomatis infection. The aim of our work was to determine the strength of the association between C trachomatis infection and plasma cell endometritis. C trachomatis infection was detected by polymerase chain reaction (PCR) or immunohistochemistry in 5 (24%) of 21 endometrial tissue samples with plasma cell endometritis and in 1 (4%) of 28 tissue samples with no evidence of plasma cell endometritis (P < .02). Patients with plasma cell endometritis were also more likely to have symptoms and signs consistent with upper genital tract chlamydial infection; thus there is an association between endometrial C trachomatis infection and the presence of plasma cells in the endometrium. The histopathologic finding of plasma cell endometritis should encourage further examination of the tissue sample for simultaneous chlamydial infection. Plasmid-based polymerase chain reaction and immunohistochemical staining of paraffin-embedded samples are useful methods for detecting C trachomatis in endometrial tissue.     

Gamma interferon-mediated cytotoxicity related to murine Chlamydia trachomatis infection.

After infection with the mouse pneumonitis agent (MoPn; murine Chlamydia trachomatis), heterozygous (nu/+) but not nude athymic (nu/nu) mice produced enhanced amounts of gamma interferon (IFN-gamma) in vitro in response to MoPn antigen that exhibited cytotoxic activity when added to host cells already infected with chlamydiae. Antibody-complement lysis showed the cytotoxic activity to be dependent, at least in part, on L3T4+ T cells for production. The cytotoxic responses were directed primarily against Chlamydia-infected target cells, but a second type of toxicity was demonstrable against uninfected target cells after treatment of the generating cell population with anti-Lyt-2 antibody plus complement at certain time points after infection. This additional nonspecific cytotoxic activity was presumably due to a second factor (factor X) acting in concert with IFN-gamma. Lyt-2+ cells, however, also were shown to play a role in IFN-gamma production and cytotoxicity directed against infected targets at later time points after infection. Neutralization of IFN-gamma in the samples containing cytotoxic activity abrogated the cytotoxicity against both infected and uninfected targets, but cloned murine IFN-gamma exhibited toxicity in a dose-dependent manner only against infected target cells. The data provides evidence that cytotoxicity against infected targets is due to antigen-specific induction of IFN-gamma, but other cytokine activity, most demonstrable after removal of Lyt-2.2+ cells and cytotoxic to uninfected targets, also is present.     

Characteristics of Chlamydia trachomatis infection in hospitalized infants with lower respiratory tract infection.

BACKGROUND AND PURPOSE: To study the epidemiology, presentation and laboratory findings of Chlamydia trachomatis pneumonia in hospitalized infants younger than 6 months. METHODS: Between January 2001 and December 2005, infants younger than 6 months admitted to the children's medical center of Taipei Veterans General Hospital with the diagnosis of acute bronchiolitis, bronchopneumonia or pneumonia were prospectively studied. Chest radiograph findings were reviewed in all patients. Basic laboratory examinations performed included white blood cell count and eosinophil count. C. trachomatis was detected via enzyme-linked immunosorbent assay antigen test and the titers of immunoglobulin G and immunoglobulin M by indirect immunoperoxidase assay. RESULTS: A total of 60 infants, 32 males and 28 females, were included. C. trachomatis infection was detected in 30% of patients (18/60). The median age was 2.5 months (range, birth to 6 months). Fever was not detected in 72% of patients (13/18). Only 22% (4/18) of these patients had the characteristic staccato cough. The mean duration of symptoms before admission was 8 days (range, 1 day to 2 months). Rhinorrhea was a prodromal symptom in 67% (12/18) of patients, with a mean pre-onset duration of 7 days (range, 1 to 14 days). Eighty three percent (15/18) of the patients had tachypnea, with a mean duration of 3.2 days (range, 1 to 7 days). Conjunctivitis was noted before admission in 6 patients (33%). Only peripheral eosinophils showed statistically significant difference between Chlamydia-positive and -negative disease (p=0.046), and may be clinically useful in cases of suspected C. trachomatis infection. Mixed infection with other pathogens including adenovirus, respiratory syncytial virus, Mycoplasma pneumoniae, cytomegalovirus and Streptococcus pneumoniae was found in 27% (5/18) of patients. CONCLUSIONS: C. trachomatis is not infrequent and plays an important role in infants younger than 6 months old hospitalized due to lower respiratory tract infection.