CD8+T cells recognize an inclusion membrane-associated protein from the vacuolar pathogenChlamydia trachomatis

During infection withChlamydia trachomatis, CD8+T cells are primed, even though the bacteria remain confined to a host cell vacuole throughout their developmental cycle. Because CD8+T cells recognize antigens processed from cytosolic proteins, theChlamydiaantigens recognized by these CD8+T cells very likely have access to the host cell cytoplasm during infection. The identity of theseC. trachomatisproteins has remained elusive, even though their localization suggests they may play important roles in the biology of the organism. Here we use a retroviral expression system to identify Cap1, a 31-kDa protein fromC. trachomatisrecognized by protective CD8+T cells. Cap1 contains no strong homology to any known protein. Immunofluorescence microscopy by using Cap1-specific antibody demonstrates that this protein is localized to the vacuolar membrane. Cap1 is virtually identical among the humanC. trachomatisserovars, suggesting that a vaccine incorporating Cap1 might enable the vaccine to protect against allC. trachomatisserovars. The identification of proteins such as Cap1 that associate with the inclusion membrane will be required to fully understand the interaction ofC. trachomatiswith its host cell.