Differential neutralization of spontaneous and centrifuge-assisted chlamydial infectivity

Lipopolysaccharide-binding alkylpolyamine DS-96 inhibits Chlamydia trachomatis infection by blocking attachment and entry

Vaginally delivered microbicides are being developed to offer women self-initiated protection against transmission of sexually transmitted infections such as Chlamydia trachomatis. A small molecule, DS-96, rationally designed for high affinity to Escherichia coli lipid A, was previously demonstrated to bind and neutralize lipopolysaccharide (LPS) from a wide variety of Gram-negative bacteria (D. Sil et al., Antimicrob. Agents Chemother. 51: 2811-2819, 2007, doi:10.1128/AAC.00200-07). Aside from the lack of the repeating O antigen, chlamydial lipooligosaccharide (LOS) shares general molecular architecture features with E. coli LPS. Importantly, the portion of lipid A where the interaction with DS-96 is expected to take place is well conserved between the two organisms, leading to the hypothesis that DS-96 inhibits Chlamydia infection by binding to LOS and compromising the function. In this study, antichlamydial activity of DS-96 was examined in cell culture. DS-96 inhibited the intercellular growth of Chlamydia in a dose-dependent manner and offered a high level of inhibition at a relatively low concentration (8 μM). The data also revealed that infectious elementary bodies (EBs) were predominantly blocked at the attachment step, as indicated by the reduced number of EBs associated with the host cell surface following pretreatment. Of those EBs that were capable of attachment, the vast majority was unable to gain entry into the host cell. Inhibition of EB attachment and entry by DS-96 suggests that Chlamydia LOS is critical to these processes during the developmental cycle. Importantly, given the low association of host toxicity previously reported by Sil et al., DS-96 is expected to perform well in animal studies as an active antichlamydial compound in a vaginal microbicide.

Interaction of chlamydiae with host cells and mucous surfaces

For chlamydiae, as obligate intracellular parasites, attachment to and ingestion by host cells are essential steps in reproduction. Their attachment site appears to be heat-sensitive; it has not been correlated with any morphological entity. Antibody blocks chlamydial attachment to cells and, for certain chlamydia psittaci and chlamydia trachomatis strains which are highly infective for cell cultures, N-acetylglucosamine appears to contribute to cell receptor specificity. Sialic acid residues have been suggested as receptors for other C. trachomatis strains. The guinea-pig inclusion conjunctivitis strain of C. psittaci becomes associated with the conjunctiva during incubation of inoculated tissue fragments in vitro. However, although antibody from tears neutralizes infectivity of this strain in vivo, association of the organism with tissue fragments is not inhibited, suggesting that antibody neutralization in vivo is not mediated by prevention of attachment to cells. Chlamydial infectivity for cell monolayers is greatly increased by centrifugation. The process is temperature-dependent and involves cooperative interactions between direction force and the pressure generated during centrifugation. Enhanced infectivity appears to result from changes induced in the cell surface. These changes may favour nonspecific interactions in attachment, since antibody inhibition of infectivity on static cell monolayers is overcome by centrifugation.

Protective effect of polyclonal and monoclonal antibodies against abortion in mice infected by Chlamydia psittaci

The role of antibody in preventing placental and fetal infection by Chlamydia psittaci was studied in mice. Pregnant mice were passively immunized with polyclonal sera or monoclonal antibodies (mAbs) at day 11 of gestation. The mice were intravenously challenged the following day with the virulent AB7 ovine abortion strain of C. psittaci. Mice were either killed on day 16 of gestation to determine placental and fetal chlamydial infection levels or were permitted to have and raise their young until 8 days old for comparison of survival rates. Immune sera produced a decrease in both placental and fetal infection and reduced the number of young dying in utero or shortly after birth. Polyclonal sera to the highly invasive AB7 and AB4 strains or to the invasive 1B strain were more effective than serum to the invasive AB13 strain. The B577/F3 and B577/A11 monoclonal antibodies gave almost complete protection, with only low levels of placental infection and no detectable fetal infection or decrease in survival rate. The study demonstrates that immune sera and type-specific mAbs can passively transfer resistance to placental and fetal colonization and to abortion and fetal loss in mice intravenously challenged with P. psittaci.

Localization of Chlamydia trachomatis infection by direct immunofluorescence and culture in pelvic inflammatory disease

Fifty-five women with suspected pelvic inflammatory disease underwent diagnostic laparoscopy and endometrial and tubal biopsy, with specimens for isolation of Chlamydia trachomatis and for staining with a species-specific monoclonal fluorescein-conjugated antibody to C. trachomatis were obtained from the urethra, rectum, endocervix, endometrium, tubes, and cul-de-sac. C. trachomatis was isolated from 21 patients (38%), including 10 (18%) who had positive endometrial or tubal cultures. The fluorescein-conjugated antibody stain was positive for 43 (86%) of 50 culture-positive specimens, for 14 (18%) of 78 culture-negative specimens from 21 patients who had positive cultures from other sites, and for one (0.5%) of 192 specimens from 34 patients who had negative cultures at all sites. Thus the sensitivity of direct fluorescein-conjugated antibody for culture-positive specimens was 86% and the specificity for specimens from culture-negative patients was 99%. Twelve upper genital tract specimens were positive by fluorescein-conjugated antibody only. Fluorescein-conjugated antibody staining of 50 paraffin-embedded endometrial aspirates showed extracellular or intracellular elementary bodies and or cytoplasmic inclusions in all of seven culture-positive specimens, in four of six culture-negative specimens from patients who had positive cultures at other sites, and in none of 34 specimens from patients with negative cultures. Thus fluorescein-conjugated antibody staining is useful for confirming the role of C. trachomatis in endometritis and salpingitis. It is more sensitive than culture for detection of chlamydia in endometrial or tubal specimens and is able to confirm that the organism is actually present in endometrial tissue (rather than simply reflecting contamination from the cervix) in women with clinical evidence of pelvic inflammatory disease.

In vitro neutralization of Chlamydia trachomatis with monoclonal antibody to an epitope on the major outer membrane protein

A murine monoclonal antibody, which binds to an epitope on the major outer membrane protein of Chlamydia trachomatis and with species specificity in the micro-immunofluorescent assay, effectively neutralized in vitro two antigenically distinct serovars of C. trachomatis. Optimal concentrations of both organism and antibody were required to produce maximal neutralization of the organism. Neutralization was less effective and more variable at lower dilutions of antibody than at higher dilutions, suggesting a prozone phenomenon. A radiolabeled attachment assay demonstrated that attachment of elementary bodies was unaffected by earlier treatment with antibody and that neutralization occurred at a step after attachment. The epitope to which this antibody is directed, on the major outer membrane protein of C. trachomatis, may have an important role in determining infectivity of the organism.

Cytotoxic cells induced after Chlamydia psittaci infection in mice

The ability of spleen cells from Chlamydia psittaci-infected mice to lyse C. psittaci-infected and uninfected target cell monolayers was studied. The cytotoxicity assay used was a terminal label method in which the number of adherent target cells surviving the interaction with effector cells was determined by measuring the uptake of [3H]uridine by such cells. It was observed that in the first few days postinfection (3 to 5), spleens contained cells that lysed infected and uninfected targets with equal efficiency. Subsequently, infected targets were killed primarily. The activity of effector spleen cells for infected targets continued, although at a reduced level, beyond 21 days postinfection. Intact effector cells were required since a disruption by sonication resulted in a loss of cytotoxicity. The enhanced killing observed with infected targets was also observed when target cells were sensitized with heat- or UV-inactivated C. psittaci. This study suggests that the induction of cytotoxic cells after C. psittaci infection may contribute to the ability of the host to control multiplication of the microorganism.

Chlamydia trachomatis infection in patients with laparoscopically verified acute salpingitis. Results of isolation and antibody determinations

Culture and serology studies have shown Chlamydia trachomatis (CT) to be one of the causes of acute salpingitis (AS). In the present investigation, results of cervical cultures were correlated with serum antibody titers to CT in patients with laparoscopically verified AS. Serum samples from 206 patients, including paired sera from 80, were assayed. Of 206 patients, 118 had chlamydial IgG antibody titers of 1:64 or more. Patients with negative cultures for CT and an IgG titer of 1:64 or more had a significantly higher geometric mean titer than corresponding patients with positive cultures. In paired sera, a seroconversion or a fourfold or greater rise in IgG titer to CT was demonstrated in 35%, while a further 11% had detectable IgM antibody in a titer of 1:8 or more. The overall isolation frequency of CT was 33%, compared with 19% for Neisseria gonorrhoeae.