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Rickettsiae are small bacteria that grow inside cells. There are several species, which are transmitted by fleas, lice, ticks or mites and cause different kinds of disease. Rickettsia typhi causes so-called endemic typhus, leading to severe complications in some cases. It may occur worldwide.
We use various mouse models to study mechanisms of the immune system that may overcome the infection. Although rickettsiae grow inside host cells, the cytotoxic activity of T cells (CD8+ lymphocytes), which usually kill infected cells, appear not to play a superior role. Interestingly, helper T cells (CD4+ lymphocytes) were found to be of pivotal importance: Apparently, R. typhi invades phagocytes of the immune system, neutrophils and macrophages, without being recognised by these cells. Only if the phagocytes are activated by helper T cells, they mobilise their weapons and are able to kill the invaders.
Kristin Moderzynski, Stefanie Papp, Liza Heine, Jessica Rauch, Svenja Kühl, Ulricke Richardt, Heidelinde Müller, Bernhard Fleischer and Anke Osterloh