As an approach to understanding chlamydial-host cell interactions and the immunobiology of Chlamydia infections, I have begun the molecular cloning of chlamydial antigens. The screening of genomic banks has been done primarily with immunological reagents developed by H. Caldwell. Numerous recombinant clones have been recovered that express surface antigens of Chlamydia trachomatis and C. psittaci. Two sets of recombinant clones--those expressing portions of the major outer membrane protein (MOMP) of C. trachomatis and those expressing the chlamydial genus-specific lipopolysaccharide (LPS) epitope--have been studied in some detail. We have found that the MOMP gene has unusual expression properties in Escherichia coli and that the chlamydial genus-specific LPS epitope is expressed on the surface of enteric bacteria harboring the LPS recombinant plasmids. Expression of the genus-specific epitope in various LPS chemotypes has allowed us to surmise the nature of the epitope. Initial studies in a primate model system indicate that oral vaccination with recombinants expressing the genus-specific epitope provides some protection against subsequent chlamydial disease. I have also cloned genes from C. trachomatis and C. psittaci that encode proteins that bind eucaryotic cell surface components and are present on the infectious form of Chlamydia but are not present on the noninfectious form.
