The present invention provides nucleic acids, proteins and vectors for a method of nucleic acid, including DNA, immunization of a host, including humans, against disease caused by infection by a strain of Chlamydia, specifically C. pneumoniae. The method employs a vector containing a nucleotide sequence encoding an ATP-binding cassette of a strain of Chlamydia pneumoniae and a promoter to effect expression of the ATP-binding cassette gene product in the host. Modifications are possible within the scope of this invention.