Effects of corticosteroids and cyclophosphamide on a mouse model of Chlamydia trachomatis pneumonitis

Anthrax toxin component, Protective Antigen, protects insects from bacterial infections

Anthrax is a major zoonotic disease of wildlife, and in places like West Africa, it can be caused by Bacillus anthracis in arid nonsylvatic savannahs, and by B. cereus biovar anthracis (Bcbva) in sylvatic rainforests. Bcbva-caused anthrax has been implicated in as much as 38% of mortality in rainforest ecosystems, where insects can enhance the transmission of anthrax-causing bacteria. While anthrax is well-characterized in mammals, its transmission by insects points to an unidentified anthrax-resistance mechanism in its vectors. In mammals, a secreted anthrax toxin component, 83 kDa Protective Antigen (PA83), binds to cell-surface receptors and is cleaved by furin into an evolutionary-conserved PA20 and a pore-forming PA63 subunits. We show that PA20 increases the resistance of Drosophila flies and Culex mosquitoes to bacterial challenges, without directly affecting the bacterial growth. We further show that the PA83 loop known to be cleaved by furin to release PA20 from PA63 is, in part, responsible for the PA20-mediated protection. We found that PA20 binds directly to the Toll activating peptidoglycan-recognition protein-SA (PGRP-SA) and that the Toll/NF-κB pathway is necessary for the PA20-mediated protection of infected flies. This effect of PA20 on innate immunity may also exist in mammals: we show that PA20 binds to human PGRP-SA ortholog. Moreover, the constitutive activity of Imd/NF-κB pathway in MAPKK Dsor1 mutant flies is sufficient to confer the protection from bacterial infections in a manner that is independent of PA20 treatment. Lastly, Clostridium septicum alpha toxin protects flies from anthrax-causing bacteria, showing that other pathogens may help insects resist anthrax. The mechanism of anthrax resistance in insects has direct implications on insect-mediated anthrax transmission for wildlife management, and with potential for applications, such as reducing the sensitivity of pollinating insects to bacterial pathogens.

Steroids alone or as adjunctive therapy with doxycycline fail to improve oviduct damage in mice infected with Chlamydia muridarum

In women, Chlamydia trachomatis can ascend from the cervix to the fallopian tubes, where an overly aggressive host inflammatory response can cause scarring that leads to chronic pelvic pain, infertility, or ectopic pregnancy. Although screening and treatment programs for women have resulted in decreased rates of sequelae, morbidities associated with oviduct scarring continue to occur. Since corticosteroids have anti-inflammatory and antifibrotic effects, we tested the ability of dexamethasone to inhibit inflammation and prevent oviduct scarring in mice genitally infected with Chlamydia muridarum. The administration of 1 or 2.5 mg/kg of body weight of dexamethasone on days 7 to 21 of infection resulted in reduced accumulation of inflammatory cells in the oviducts compared to that in controls. However, a concomitant increase in bacterial burden was observed, and chronic oviduct disease was not reduced. Adjunctive administration of a prolonged (21-day) or short (3-day) course of dexamethasone in combination with the antibiotic doxycycline also failed to reduce chronic oviduct pathology compared to antibiotic treatment alone. Steroids administered alone or adjunctively with antibiotics failed to prevent oviduct damage in this murine model of C. trachomatis infection.

Reactivation of chlamydial genital tract infection in mice

A model was developed to study chlamydial quiescence in C3H/HeN (C3H) and C57BL/6N (C57) mice following genital tract infection by Chlamydia trachomatis MoPn. Reactivation of chlamydial shedding following immunosuppression indicated that viable MoPn remained in the genital tract for up to 4 or 5 weeks after the apparent clearance of a primary infection. Either cyclophosphamide or cortisone acetate treatment could cause reactivation, but cyclophosphamide was more effective. However, the frequency of reactivation by either drug diminished with time in both mouse strains. Progesterone treatment prior to infection of C57 mice greatly reduced the frequency of reactivation by cyclophosphamide and also correlated with the development of marked fluid accumulation and distension of the uterine horns in the vast majority of those animals. This pathology was apparent by 5 to 7 weeks postinfection and was consistently seen through 110 days postinfection. Neither of these phenomena was observed in C57 mice that had not been treated with progesterone or in C3H mice under any conditions tested. The infecting dose of MoPn did not clearly influence the frequency of reactivation in either inbred strain as defined by this model.

Effect of hydrocortisone succinate on growth of Chlamydia pneumoniae in vitro

We examined the effect of hydrocortisone succinate on the growth of three isolates of Chlamydia pneumoniae in vitro. There was a significant increase in the number of inclusions seen in two of the C. pneumoniae strains in the presence of hydrocortisone. There was no significant increase in the number of inclusions with various concentrations of hydrocortisone over time. The addition of hydrocortisone did not affect the in vitro activities of azithromycin, erythromycin, and doxycycline against C. pneumoniae.

Experimental Chlamydia psittaci infection of Japanese quail

Japanese quail were used for the infection model of avian chlamydiosis. One-day-old Japanese quail were highly susceptible to lethal infection by a Chlamydia psittaci strain of budgerigar origin upon inoculation via the air sac route with 10(4.1) FFU of the organism, showing an acute and lethal course with chlamydial propagation. In contrast, 7-day-old quail developed resistance to the infection as shown by the lack of lethal effect with the same dose. The resistance of 7-day-old birds was abolished by immunosuppressive treatment with cyclophosphamide. Upon inoculation with a sublethal dose of 10(2.1) FFU, latent infection was established in 1-day-old birds with a minimum number of the organism. The latent infection in the birds was converted to the lethal form by treatment with cyclophosphamide along with chlamydial propagation and suppression of antibody production.

Reactivation of Chlamydia pneumoniae infection in mice by cortisone treatment

Reactivation of Chlamydia pneumoniae infection was studied by inducing immunosuppression by cortisone acetate treatment given every other day for 14 days in intranasally infected NIH/s mice. The treatment started 2 or 4 weeks after primary infection, when no C. pneumoniae was detected. C. pneumoniae could be recovered from the lung cultures on days 7 and 9 in 10 and 60% of the mice, respectively, when cortisone treatment was begun 30 days after infection. These results confirm the persistent nature of C. pneumoniae infection.

Identification of Chlamydia trachomatis antigens by use of murine T-cell lines

Chlamydia-specific short-term T-cell lines were used in conjunction with immunoblot techniques to examine Chlamydia trachomatis proteins for T-cell-stimulatory activity. This study was undertaken because of the known role of T cells in the resolution and pathogenesis of chlamydial infections. Therefore, determination of which chlamydial proteins are T-cell antigens and whether they evoke protective immunity or contribute to immunopathology is crucial. Immune lymph node cells were stimulated with whole chlamydial organism (elementary body) to derive predominantly CD4+ T-cell lines. Proteins from the elementary body and the outer membrane and cloned proteins were examined for antigenicity with these T-cell lines in a proliferation assay. Although a majority of the elementary body protein fractions were positive in this assay, only four of the outer membrane fractions were stimulatory. The cloned major outer membrane protein and outer membrane protein 2 were stimulatory in the assay and may account for the reactivity in three of the four positive outer membrane fractions. The C. trachomatis heat shock protein 60, examined because of its putative role in causing delayed-type hypersensitivity, was found to stimulate the CD4+ T cells. This approach with short-term T-cell lines with polyclonal reactivity was sensitive and specific in identifying chlamydial proteins as T-cell antigens.

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.