Prior genital tract infection with a murine or human biovar of Chlamydia trachomatis protects mice against heterotypic challenge infection

Abstract

We sought to assess the degree of cross-protective immunity in a mouse model of chlamydial genital tract infection. Following resolution of genital infection with the mouse pneumonitis (MoPn) biovar of Chlamydia trachomatis, mice were challenged intravaginally with either MoPn or human serovar E or L2. The majority of animals previously infected with MoPn were solidly immune to challenge with either of the two human biovars. Surprisingly, approximately 50% of animals became reinfected when homologously challenged with MoPn, although the secondary infection yielded significantly lower numbers of the organism isolated over a shorter duration than in the primary infection. Primary infection with serovar E also protected against challenge with MoPn or serovar L2, although the degree of immune protection was lower than that resulting from primary infection with MoPn. Blast transformation and assessment of delayed-type hypersensitivity indicated that mice previously infected with either human or murine biovars produced broadly cross-reactive T cells that recognized epitopes of either murine or human biovars of C. trachomatis. Immunoblotting demonstrated that primary MoPn infection produced immunoglobulin G (IgG) antibody to antigens of MoPn as well as at least three distinct antigenic components of human serovar E, one of which was identical in molecular weight to the major outer membrane protein (MOMP). Primary infection with serovar E produced IgG antibody reactive against serovar E but not MoPn MOMP and against at least one ca. 60-kDa protein of both chlamydial strains. Our results indicate that primary genital infection of mice with murine C. trachomatis induces immunity against challenge with either of two human biovars.

FIG. 1

Primary murine genital tract infection with MoPn C. trachomatis protects against homotypic and heterotypic challenge. The course of infection is shown by solid lines, with each point representing mean IFU from cervical-vaginal swabs of culture-positive mice collected at the time points indicated. Above each point is the ratio of the number of culture-positive animals to the total number of animals in each group. Symbols: ●, previously uninfected controls; ■, mice previously infected with MoPn. (A) Mice challenged with human serovar E (total of two experiments). (B) Mice challenged with human serovar L2 (total of one experiment). (C) Mice challenged with MoPn (total of three experiments).

FIG. 2

Primary murine genital infection with C. trachomatis serovar E protects against homotypic and heterotypic challenge. The course of infection is shown by solid lines, with each point representing mean IFU from cervical-vaginal swabs of culture-positive mice collected at the time points indicated. Above each point is the ratio of the number of culture-positive animals to the total number of animals in each group. Symbols: ●, previously uninfected controls; ■, mice previously infected with serovar E. (A) Mice challenged with MoPn (total of two experiments). (B) Mice challenged with human serovar L2 (total of one experiment). (C) Mice challenged with serovar E (total of one experiment).

FIG. 3

Proliferative responses of T lymphocytes to homotypic and heterotypic chlamydial antigens (Ag). Proliferation was assessed by [³H]thymidine incorporation in quadruplicate cultures of nylon wool-enriched T lymphocytes derived from either spleen or ILN in response to UV-inactivated, gradient-purified EBs of C. trachomatis serovar E (closed bars), MoPn (shaded bars), serovar A (open bars), or serovar L2 (hatched bars). (A) Response at day 56 postinfection with serovar E. (B) Response at day 56 postinfection with MoPn. Data are expressed as mean counts per minute above HeLa 229 antigen stimulation for each experimental group (serovar E infected and MoPn infected) and T-cell origin (spleen and ILN). The responses to Hela 229 antigen (and background unstimulated controls) were as follows: ILN (A), 297 ± 91 (176 ± 63); spleen (A), 1,151 ± 217 (927 ± 242); ILN (B), 303 ± 143 (148 ± 54); spleen (B), 2,524 ± 760 (532 ± 158).

FIG. 4

IgG antibody reactivity at day 56 postinfection with a mouse or human biovar of C. trachomatis. Solubilized gradient-purified EBs of serovar E (lanes A and D) or MoPn (lanes B and C) resolved on 4 to 12% gradient gels and transferred to nitrocellulose were probed with immune plasma collected at day 56 postinfection from a mouse infected with MoPn (lanes C and D) or a mouse infected with serovar E (lanes A and B). Similar results were obtained from a total of eight mice tested (four each MoPn- and serovar E-infected animals). The exposed film was developed and scanned on a Microtek Scanmaker E3 with Photoshop 3.0.5 software. The scanned image was prepared and labeled with QuarkXpress 3.32.