The effect of immunization route on rat serum and tear antibody responses to Chlamydia trachomatis

The effect of immunization route on the kinetics of serum and tear antibody responses to Chlamydia trachomatis was studied in a rat model. Rats received Chlamydia trachomatis serovar C/TW elementary bodies for two immunization cycles by ocular topical (OT) application or subconjunctival (SC) injection and in a second experiment for three immunization cycles by either OT application, gastrointestinal intubation (GI), or intraperitoneal injection (IP). Serum IgG and tear IgA antibodies to whole elementary bodies were measured sequentially following the secondary (2 degrees) and tertiary (3 degrees) immunization cycles. Serum IgG levels were minimal in the OT immunized group following 2 degrees and 3 degrees immunization. Serum IgG levels for the SC, GI, and IP immunized groups rose steadily following 2 degrees immunization reaching maximal levels between day (d)24 and d31. Levels of serum IgG antibodies were highest in the GI group following 3 degrees immunization. Tear IgA antibody responses were greatest in rats immunized by the OT route, the 2 degrees IgA response peaked by d9 and declined by d24. The 3 degrees OT tear IgA response peaked by d13 and was greater than the 2 degrees response. Tear IgA antibody levels in SC and GI immunized rats appeared by d3 following 2 degrees immunization but remained at low levels and were not noted until d20 in the GI group following 3 degrees immunization. Tear IgA antibody responses were not detectable in IP animals following 2 degrees or 3 degrees immunization. This study documents the immunogenicity of Chlamydia trachomatis serovar C/TW in the rat and shows that the OT route is most effective in eliciting IgA antibody responses in tears.