Most chlamydiae live in natural environments but not in humans. – What kinds of features do they need to cause human disease? –
Department of Microbiology and Immunity, Nippon Medical School
Chlamydiae are obligate intracellular bacteria and known as human pathogens. For example, Chlamydia trachomatis is not only a cause of preventable blindness, but also a common pathogen causing sexual transmitted diseases. However, it is known that only a few chlamydiae can infect human and cause human diseases, but the others cannot survive in human. Some chlamydiae living in protozoa such as Acanthamoeba are called environmental chlamydiae whereas chlamydiae infecting vertebrates including human are called pathogenic chlamydiae. Ancient chlamydiae divided into environmental chlamydiae and pathogenic chlamydiae about 700 million years ago, and they have evolved to adapt themselves to their hosts. Since pathogenic chlamydiae need to escape from their host’ s immune systems, they have evolved not to induce the immune response severely. In addition, pathogenic chlamydiae such as C. trachomatis can inhibit apoptosis to protect their replicating niche in the host cells. On the other hand, we showed that one of environmental chlamydiae, Protochlamydia, induces apoptosis when infecting to HEp-2 cells, which are established human epithelial cells, and it can never replicate in the cells. Furthermore, Parachlamydia acanthamoebae Bn9 that is an environmental chlmaydia living in amoeba can increase in HEp-2 cells at 32 _C, although it cannot survive in the cells at 37 _C that is a suitable temperature for human cells. We also revealed that Protochlamydia sp. HSTS living in amoebas isolated from a hot spring can grow in HEp-2 cells at 37 _C. From these results, it is suggested that the regulation of apoptosis and the adaptation to the human temperature is critical for the chlamydial surviving in human. Thus, there is a possibility that some environmental chlamydiae can cause human diseases, though they have evolved to adapt to their hosts. To determine the features of environmental chlamydiae would be important to prevent unknown chlamydial infectious diseases.
keywords:Environmental chlamydiae,Pathogenic chlamydiae,Intracellular bacterium