Immunoelectron microscopic localisation of the OMP90 family on the outer membrane surface of Chlamydia psittaci

The putative outer membrane location of the OMP90 (formerly POMP) family from the ovine abortion strain of Chlamydia psittaci was investigated by immunoelectron microscopy. Using a non-embedding technique, antigens were shown to be localised on the outer membrane surface of both elementary and reticulate bodies, the infectious and non-infectious forms of Chlamydiae respectively. Antibodies affinity-purified against the expressed amino- and carboxy-terminal halves of one of the family members. OMP90A, demonstrated that the amino half is surface-exposed while the carboxyl half is most probably localised internally. Surface localisation on elementary bodies indicates the importance of these proteins as protective antigen candidates.