Figure 6.

Only early transfer of C. psittaci-specific antibodies partially protects C3aR^−/− mice from severe pneumonia and increases their survival rate. Survival of mice (A) was statistically analyzed with the Log-rank (Mantel-Cox) test. Body weight (B) was analyzed with 2-way ANOVA and Bonferroni Posttest. Ten C3aR^−/− mice received C. psittaci-specific hyperimmune serum one day before infection, 8 mice received this serum 7 d p.i., and n = 8 mice received only control serum. Hyperimmune serum was positive in the anti-C. psittaci ELISA for IgG, in contrast to pooled serum of not-infected mice providing control serum (data not shown). After the transfer of hyperimmune serum, C. psittaci-specific IgG reached levels similar to those observed 2 or 3 weeks after primary infection of WT mice (data not shown). Mice were monitored for up to 35 days to determine survival rates. Means ± standard errors of the means are depicted. Asterisks indicate significant differences between infected C3aR^−/− recipient mice receiving C. psittaci-specific serum 1 day before or 7 days after chlamydial infection, or control serum one day before infection (*P ≤ .05; **P ≤ .01; ***P ≤ .001). Abbreviations: ANOVA, analysis of variance; C3aR, C3a receptor; d p.i., days postinfection; ELISA, enzyme-linked immunosorbent assay; IgG, immunglobulin G; WT, wild type.