Recombinant Chlamydia pneumonia antigen, produced in E.coli is derived from the CP major outer membrane protein (this region is recognized only by Chlamydia pneumonia antibody), it contains 160 amino acids and fused with a His Tag at C-terminus, having an MW of about 18kDa, the protein forms a monomer and a dimer on SDS-PAGE gel,the majority of the protein forms a dimer, which migrates at an MW of 40kDa. Chlamydia pneumonia is purified by proprietary chromatographic technique.