Figure 2.
Protective immunity induced by the Fc fusion protein of the chlamydial major outer membrane protein (Fc-MOMP) is related to Chlamydia-specific T helper type 1 (Th1) cells in the genital mucosa. Two groups of C57BL/6 mice were vaccinated with either Fc-MOMP or the control, Fc fusion protein of the protective glycoprotein D2 antigen of herpes simplex virus type 2 (Fc-gD2), and then challenged with mouse pneumonitis (1 × 105 inclusion-forming units per mouse). Two weeks after challenge, the infection status was assessed by swabbing the cervicovaginal vaults, and chlamydiae were isolated in tissue cultures, as described in the Materials and Methods. Data are expressed as the percentage of animals in which infection resolved within 2 weeks. At the same time, T cells were isolated from the reproductive tissues of each group, and the frequency of Chlamydia-specific Th1 cells was determined by a limiting dilution technique, as described in the Materials and Methods. T cells from naive mice had a Chlamydia-specific Th1 frequency of 15 (range, 9–21), similar to the frequency measured in the control group that received Fc-gD2. The experiment was repeated twice, with 6 mice per experimental group.