he objective of this project is to identify peptide ragment(s) of the Chlamydia trachomatis major outer membrane rotein (MOMP) that possess type-specific antigenic roperties. This antigenic determinant is highly mmunoaccessible on viable chlamydiae and has been identified s a potential peptide candidate for the development of a C. rachomatis vaccine. Peptide fragments of MOMP were generated y Cyanogen bromide (CNBr) cleavage and Staphylococcus aureus 8 protease digestion. The antigenic properties of peptides ere analyzed by immunoblotting with monoclonal antibodies that ecognize type-, subspecies-, and species-specific epitopes ocated on the same MOMP polypeptide. Limited proteolysis of OMP with V8 protease resulted in nine immunoreactive peptides anging in molecular weight from 7Kd to 25Kd when probed with olyclonal anti-MOMP IgG. Two of these fragments (13Kd and 8Kd) reacted with the subspecies- and species-specific MOMP onoclonal antibodies, indicating that these epitopes are losely associated on the intact MOMP polypeptide. The ype-specific monoclonal antibody, although reactive with ndigested MOMP, did not react with any of the V8 protease MOMP eptide fragments. These findings suggest that the ype-specific MOMP antigenic determinant contains or is in lose proximity to a glutamic acid residue. CNBr digestion of OMP resulted in immunoreactive peptides of 21Kd, 15Kd, and 9Kd ith polyclonal anti-MOMP IgG. The subspecies- and pecies-specific MOMP monoclonal antibodies reacted with the 1Kd and 9Kd fragments, whereas the type-specific MOMP onoclonal antibody recognized only the 15Kd peptide. The solated 15Kd fragment will be used as an immunogen to etermine its potential as a subunit or peptidic C. trachomatis accine.