Urogenital chlamydial infection, caused by Chlamydia trachomatis, is the main sexually transmitted infection in Sweden. Despite active programmes for detection and case finding, nearly 37 000 cases were reported in 2010. Serovar E strains are considered to cause approximately 40-50% of these cases. A vaccine would be highly valuable in order to control the epidemic.
The major outer membrane protein (MOMP) of Chlamydia trachomatis is a highly antigenic and hydrophobic transmembrane protein. Our attempts to express the full-length protein in a soluble form in transgenic plants failed. A chimeric gene construct of Chlamydia trachomatis serovar E MOMP was designed in order to increase solubility of the MOMP protein but with retained antigenicity. The construct was based on known T and B cell epitopes located in the variable segment (VS) 2 and 4 loops of MOMP.
The designed construct was successfully expressed in Arabidopsis thaliana, and in Daucus carota. A chimeric MOMP expressed in and purified from E. coli was used as antigen for production of antibodies in rabbits. The anti-chimeric MOMP antibodies recognized the corresponding protein in the transgenic plants, as well as in inactivated C. trachomatis elementary bodies. Transgenic Arabidopsis and carrots were characterized for the number of MOMP chimeric genetic inserts and for protein expression. Stable integration of the transgene and the corresponding protein expression were demonstrated in Arabidopsis plants over at least six generations. Transgenic carrots showed a high level of expression of the chimeric MOMP– up to 3% of TSP.