Kinetics of adaptive B-cell immune response following B microti infection in Townes SS and control mice. Groups of Townes SS mice along with control AA and AS mice were infected with 1 × 10⁷ to 1 × 10⁸B microti–parasitized RBCs intraperitoneally and a representative experiment is shown. (A) The frequency of peripheral blood erythrocytes infected with B microti in total number of RBCs. (B) The spleen weights of AA, AS, SS mice before and after infection. (C) Representative FACS plots for GL7 and FAS gated on B220⁺ cells for the identification of GC B cells in the spleens from AA, AS, and SS mice. (D) Quantification of GC B cells in the spleens from AA, AS, and SS mice on days indicated before and following infection. (E) Representative FACS plots for B220 and CD138 for the identification of plasma cells. (F) Quantification of plasma cells in the spleens from AA, AS, and SS mice. Each symbol represents data from an individual mouse. Error bars indicate the mean ± SEM. **P < .01; ***P < .001; ****P < .0001 by unpaired 2-tailed Student t test. ns, not significant.