An intermolecular mechanism of T cell help for the production of antibodies to the bacterial pathogen, Chlamydia trachomatis.

Antibodies that neutralize infectivity are directed at the antigenically variant major outer membrane protein (MOMP) of Chlamydia trachomatis. A vaccine for chlamydia will need to include T cell determinants that elicit T helper (Th) cells which provide help to MOMP-specific B cells. A limited number of determinants on MOMP are able to elicit Th cells and sequence diversity in the MOMP molecule may alter T cell recognition of these determinants. We investigated whether two sequence invariant proteins of C. trachomatis that are both abundant and immunogenic could elicit T cell help for the production of antibody to MOMP. We found that outer membrane protein 2 (OMP2) but not outer membrane protein 3 (OMP3) was able to prime BALB/c mice for an anamnestic anti-MOMP response following boost with the intact organism. This demonstration of an intermolecular mechanism of T cell help in a bacterial system has important implications for the development of a chlamydial vaccine as well as the design of vaccines for other antigenically variant non-viral pathogens.