Nonpathogenic Colonization with Chlamydia in the Gastrointestinal Tract as Oral Vaccination for Inducing Transmucosal Protection.

has been detected in the gastrointestinal tracts of humans and animals. We now report that gastrointestinal is able to induce robust transmucosal protection in mice. colonization in the gastrointestinal tract correlated with both a shortened course of genital tract infection and stronger protection against subsequent genital tract challenge infection. Mice preinoculated intragastrically with became highly resistant to subsequent infection in the genital tract, resulting in prevention of pathology in the upper genital tract. The transmucosal protection in the genital tract was rapidly induced, durable, and dependent on major histocompatibility complex (MHC) class II antigen presentation but not MHC class I antigen presentation. Although a deficiency in CD4 T cells only partially reduced the transmucosal protection, depletion of CD4 T cells from B cell-deficient mice completely abolished the protection, suggesting a synergistic role of both CD4 T and B cells in the gastrointestinal -induced transmucosal immunity. However, the same protective immunity did not significantly affect colonization in the gastrointestinal tract. The long-lasting colonization with was restricted to the gastrointestinal tract and was nonpathogenic to either gastrointestinal or extragastrointestinal tissues. Furthermore, gastrointestinal did not alter the gut microbiota or the development of gut mucosal resident memory T cell responses to a nonchlamydial infection. Thus, may be developed into a safe and orally deliverable replicating vaccine for inducing transmucosal protection.