Intranasal immunization with Chlamydia trachomatis, serovar E, protects from a subsequent vaginal challenge with the homologous serovar

To vaccinate against a vaginal challenge with Chlamydia trachomatis, C3H/HeJ (H-2(k)) mice were immunized intranasally (i.n.) or intraperitoneally (i.p.) with 1 x 10⁶ inclusion forming units (IFU) of C. trachomatis, serovar E and i.n. with 1 x 10⁶ UV inactivated IFU of serovar E. Animals inoculated i.n. with mock infected HeLa 229 cells were used as controls. Upon a vaginal challenge with 5 x 10³ IFU of serovar E, mice immunized i.n. with viable serovar E exhibited significant protection as judged by the number of mice infected compared to controls (p < 0.05). In contrast, mice immunized i.n. with serovar E that had been UV-inactivated, were not protected from a subsequent vaginal challenge with serovar E. Mice immunized i.p. with serovar E showed attenuation of the infection by 4 weeks after challenge compared to control mice as to the number of animals with positive vaginal cultures (p < 0.05). Of the immune parameters examined, the best correlation with protection was seen with Chlamydia specific IgG and IgA vaginal titers and lymphoproliferative responses to serovar E. In summary, mucosal immunization with viable serovar E partially protected mice against a subsequent vaginal challenge, thereby showing that it is possible to elicit a protective response to a human strain of C. trachomatis at a distant mucosal site in this animal model.