Studies using the guinea pig model of chlamydial genital
infection with the Chlamydia psittaci agent of guinea pig
inclusion conjunctivitis (GPIC) have shown that serum and local
antibodies play a role both in the resolution of
infection and in protection against
reinfection. Thus, this model is suited for further exploration of immune mechanisms and for
vaccine studies with chlamydial macromolecules. We have further characterized the model by assessing the
antigen-specific antibody response to experimental genital
infection by using immunoblotting to assay both genital secretions and serum. The GPIC agent was characterized by analysis of outer
membrane proteins, which indicated that the GPIC agent possessed a major outer
membrane protein (MOMP), with a molecular mass of 39 kilodaltons (kDa), and a 61-kDa
protein, analogous to
cysteine-rich 60-kDa
proteins or doublets of Chlamydia trachomatis strains. As indicated by immunoblotting, most infected animals produced serum
immunoglobulin G antibodies to MOMP, the 61-kDa
proteins, an 84-kDa outer
membrane protein, and
lipopolysaccharide. Such serum
antibodies persisted for at least 813 days after primary genital
infection.
Immunoglobulin A antibodies against the 61-kDa
proteins,
lipopolysaccharide, and MOMP, but not the 84-kDa
protein, were detected in secretions. Animals challenged with GPIC 825 days after primary
infection became infected again despite the presence of serum
antibodies, but the period of chlamydial shedding was significantly shorter and less intense than in primary
infections. Although the specific mechanism is not known, these data suggest that a long-lasting immune effect is capable of altering the course of
infection late after primary
infection. Correlation of the
antigen-specific antibody response and other immune parameters with the duration and degree of protective immunity induced by
infection or vaccination may be helpful in further understanding the nature of such protective immunity.