FIG 4.

Class- and subclass-specific anti-chlamydial antibody titers during primary and secondary infection. Serum was collected during primary infection (A), before secondary rechallenge (B), and during secondary rechallenge (C) from CD4-depleted and nondepleted C57BL/6, IFN-γ^−/−, and μMT mice, and chlamydia-specific ELISAs were performed. Indicated days represent times post-primary infectious challenge. μMT mice produced no detectable levels of chlamydia-specific antibodies at any time point. Titers of sera from individual mice were determined, and data are presented as means ± SD for 20 mice/group (C57BL/6 and μMT) or 32 mice/group (IFN-γ^−/−). *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001.