Animal models of chlamydial infection

Cross-Reactive Effects of Vaccines: Heterologous Immunity between Tetanus and Chlamydia

Vaccines can have heterologous effects on the immune system, i.e., effects other than triggering an immune response against the disease targeted by the vaccine. We investigated whether monoclonal antibodies (mAbs) specific for tetanus could cross-react with Chlamydia and confer heterologous protection against chlamydial infection. The capability of two tetanus-specific mAbs, namely mAb26 and mAb51, to prevent chlamydial infection has been assessed: (i) in vitro, by performing a neutralization assay using human conjunctival epithelial (HCjE) cells infected with Chlamydia trachomatis serovar B, and (ii) in vivo, by using a guinea pig model of Chlamydiacaviae-induced inclusion conjunctivitis. The mAb26 has been superior in comparison with mAb51 in the prevention of chlamydial infection in HCjE cells. The mAb26 has conferred ≈40% inhibition of the infection, compared to less than 5% inhibition in the presence of the mAb51. In vivo, mAb26 significantly diminished ocular pathology intensity in guinea pigs infected with C. caviae compared to either the mAb51-treated or sham-treated guinea pigs. Our data provide insights that tetanus immunization generates antibodies which induce heterologous chlamydial immunity and promote protection beyond the intended target pathogen.

Validation of the Chlamydia trachomatis genital challenge pig model for testing recombinant protein vaccines

Chlamydia trachomatis is a Gram-negative obligate intracellular bacterial pathogen that is the leading cause of bacterial sexually transmitted disease in humans in developing countries. A vaccination programme is considered to be the best approach to reduce the prevalence of C. trachomatis infections. However, there are still no commercial C. trachomatis vaccines. In order to develop effective C. trachomatis vaccines, it is important to identify those antigens that elicit a protective immune response, and to develop new and adequate methods and adjuvants for effective vaccine delivery, as conventional methods have failed to induce protective immunity. In order to test different vaccine candidates, animal models are needed. Former studies have used non-primate monkeys, mice or guinea pig infection models. The present study used a pig model for testing recombinant protein vaccines. Two recombinant proteins, polymorphic membrane protein G (PmpG), and secretion and cellular translocation protein C (SctC), were tested for their ability to create protection in a pig C. trachomatis challenge model. The vaccines were administered subcutaneously with GNE adjuvant. Six weeks later, animals were challenged intravaginally with C. trachomatis serovar E. After a further 4 weeks, the pigs were euthanized. PmpG-immunized pigs were better protected than pigs immunized with the less promising SctC candidate vaccine antigen. Interestingly, significant protection was apparently not correlated with a strong humoral immune response upon subcutaneous immunization. In conclusion, the pig model is useful for studying the efficacy of vaccine candidates against genital human C. trachomatis infection.

Genetic profiling of dendritic cells exposed to live- or ultraviolet-irradiated Chlamydia muridarum reveals marked differences in CXC chemokine profiles

Chlamydia trachomatis is a major cause of sexually transmitted disease worldwide for which an effective vaccine is being actively pursued. Current vaccine efforts will be aided by elucidating the interaction between Chlamydia and dendritic cells (DCs). Protective immunity appears to develop slowly following natural infection in humans, and early vaccine trials using inactivated C. trachomatis resulted in partial, short-lived protection with possible enhanced inflammatory pathology during re-infection. Thus, immunity following natural infection with live chlamydia may differ fundamentally from immune responses induced by immunization with inactivated chlamydia. We explored this conjecture by studying the response of DCs exposed to either viable or inactivated [ultraviolet (UV) -irradiated] chlamydia elementary bodies (EBs; designated as Live-EB and UV-EB, respectively) using Affymetrix GeneChip microarrays. Thirty-one immunologically characterized genes were differentially expressed by DCs following exposure to Live-EB or UV-EB, including two glutamic acid-leucine-arginine cysteine-X-cysteine (ELR CXC) neutrophil chemoattractant chemokines, Cxcl1 (KC), and Cxcl2 (MIP-2). Up-regulation of these genes by Live-EB as compared to UV-EB was verified by quantitative reverse transcription-polymerase chain reaction and increased chemokine secretion was confirmed by enzyme-linked immunosorbent assay both in vitro and in vivo. Immunofluorescence and fluorescence-activated cell sorter analysis of chlamydia-infected lung tissue confirmed that Live-EB but not UV-EB induced significant DC and neutrophil infiltration during infection. These observations demonstrate that the development of an antichlamydial immune response is dramatically influenced by chlamydial viability. This has implications as to why early inactivated chlamydial vaccines were ineffective and suggests that new vaccine design efforts may benefit from in vitro DC screening for ELR chemokine expression profiles.

Experimental chlamydial keratitis in rabbits. Correlation with chlamydia infected McCoy tissue culture cells

Rabbit corneas were inoculated three times at weekly intervals with the agent of chlamydia trachomatis using the scratch method. Specimens of the corneal epithelium were obtained using the replica technique on the 1st, 2nd, 3rd and 4th day after each inoculation and at two weeks after the last inoculation. The development of chlamydial inclusions and the inflammatory cell response were monitored using Giemsa stain, acridine orange stain and direct immunofluorescent technique. Primary inoculation produced mild clinical disease associated cytologically with polymorphonuclear leucocytic cellular inflammatory response. Repeated inoculations produced more severe disease associated clinically with pannus formation and cytologically with the presence of lymphocytes and Leber cells in addition to polymorphonuclear leucocytes. Halberstaedter Prowazek inclusion bodies were detected in all the specimens. Additional intracytoplasmic and intranuclear inclusions of different morphological appearances were present. The cytological findings detected in the corneal epithelium of rabbits were correlated with the findings in McCoy tissue culture cells inoculated with chlamydia trachomatis.

Ocular sensitization of mice by live (but not irradiated) Chlamydia trachomatis serovar A

Ocular exposure of mice to live elementary bodies of Chlamydia trachomatis serovar A results in immunological sensitization of the mice. This reactivity is manifested by the development of early (5 h) and delayed-type (24 h) dermal reactivity and serovar-specific antibody formation against either live or irradiated (100 kilorads) elementary bodies. Parallel ocular exposure of mice to irradiated elementary bodies does not result in this sensitization. The early and late dermal immune responses induced by ocular exposure to live organisms can be transferred to unexposed mice by serum and lymphoid cell transfers, respectively. It appears that successful murine ocular sensitization by human C. trachomatis serovar A elementary bodies is an ability manifested by live organisms and not by inactivated but antigenic organisms.

Etiology of cervical inflammation

We studied the relationships of selected microbial, clinical, demographic, and behavioral variables to mucopurulent cervicitis in two clinical settings, a sexually transmitted disease clinic and a student health clinic. From each clinic, we studied a group of women referred for suspected mucopurulent cervicitis and a representative sample of other women attending the clinic. After the women were stratified by patient group and summary odds ratios for all groups were obtained, mucopurulent cervicitis was most strongly associated with the isolation of Chlamydia trachomatis; other variables associated with mucopurulent cervicitis included the isolation of Ureaplasma urealyticum, Gardnerella vaginalis, and Trichomonas vaginalis, the presence of serum antibody to C. trachomatis, the clinical diagnosis of bacterial vaginosis, and oral contraceptive use (positive associations) or isolation of yeast (negative association). After adjustment for cervical culture results for C. trachomatis, mucopurulent cervicitis was positively associated with oral contraceptive use (p = 0.02) and isolation of U. urealyticum (p = 0.02) and negatively associated with isolation of yeast (p = 0.03). Among women with a positive cervical culture for C. trachomatis, isolation of U. urealyticum was significantly associated with mucopurulent cervicitis, while among the subgroup of women with a negative cervical culture for C. trachomatis and positive serum antibody to C. trachomatis, oral contraceptive use was strongly associated with mucopurulent cervicitis. These results confirm that in both clinical settings C. trachomatis is the major cause of mucopurulent cervicitis. The roles of U. urealyticum, T. vaginalis, G. vaginalis, bacterial vaginosis, and oral contraceptive use in the etiology of mucopurulent cervicitis deserve further study.