| Summary: | <p>Abstract</p> <p>Background</p> <p>Chlamydiae are obligate intracellular bacteria, which are important human pathogens. Genome sequences of <it>C. trachomatis </it>and <it>C. pneumoniae </it>have revealed the presence of a <it>Chlamydia </it>specific gene family encoding polymorphic outer membrane proteins, Pmps. In <it>C. pneumoniae </it>the family comprises twenty-one members, which are all transcribed. In the present study, the expression, processing and localisation of the sixteen full-length Pmps in <it>C. pneumoniae </it>strain CWL029 have been further investigated by two-dimensional gel electrophoresis and immunofluorescence microscopy.</p> <p>Results</p> <p>Ten Pmps were identified in elementary bodies (EBs). Eight of these were investigated with respect to time dependent expression and all were found to be up-regulated between 36 and 48 hours post infection. Antibodies against Pmp6, 8, 10, 11 and 21 reacted with chlamydiae when infected cells were formalin fixed. Pmp6, Pmp20 and Pmp21 were found in cleaved forms, and the cleavage sites of Pmp6 and Pmp21 were identified.</p> <p>Conclusions</p> <p>The Pmps are heavily up-regulated at the time of conversion of RB to EB, and at least ten Pmps are present in EBs. Due to their reaction in formalin fixation it is likely that Pmp6, 8, 10, 11 and 21 are surface exposed. The identified cleavage sites of Pmp6 and Pmp21 are in agreement with the theory that the Pmps are autotransporters.</p>
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