Uptake and processing of Chlamydia trachomatis by human dendritic cells.

Chlamydia trachomatis (CT) causes several sexually transmitted diseases. In 2-5% of cases, CT infection leads to the development of reactive arthritis. Dendritic cells (DC) are central in T cell priming and the induction of antigen specific immunity. Here we have studied the uptake and processing of CT serovar L2 by human DC, and their ability to present CT antigens to both CD4(+) and CD8(+) T cells. We show that the entry of CT was mediated by the attachment of CT to heparan sulfates and could be inhibited by heparin. There was no inhibition of uptake by an agent which blocks micropinocytosis. Infecting DC with CT led to their activation and the production of IL-12 and TNF-alpha but not IL-10. Following invasion, CT was confined to distinct vacuoles which were visualized with anti-CT antibodies using confocal microscopy. Unlike with epithelial cells, these vacuoles did not develop into characteristic inclusion bodies. In the first 48 h, CT(+) vacuoles were negative for Lamp-1 and MHC class II. Despite no obvious co-localization between CT vacuoles and MHC loading compartments, infected DC efficiently presented CT antigens to CD4(+) T cells. Infected DC also expanded CT specific CD8(+) T cells, allowing us to generate a number of CT-reactive CD8(+) T cell clones. There is still controversy about the importance of chlamydia-specific CD8(+) T cell responses in patients with arthritis. This is largely due to the difficulties in studying CTL responses at the clonal level. The use of DC as antigen-presenting cells should enable more detailed characterization of these CTL responses.