Analysis of splenic follicles of Townes SS and control mice before and following B microti infection. Representative immunohistochemical staining of splenic follicles in Townes SS and control AA and C57BL/6 mice before (A) or after (B, on day 10) B microti infection. Splenic sections were stained for B220 (and detected using horseradish peroxidase (HRP)–linker antibody conjugate with DAP as substrate, brown) and CD3 (and detected using HRP-linker antibody conjugate with DAP as substrate, brown) (n = 2-3 mice). T cells and follicular B cells (FOB) are localized in nonoverlapping areas in the spleens from naive, uninfected C57BL/6, and AA mice. Spleens from naive, uninfected SS mice shows very small indistinct follicles. Following Babesia infection (B), large GCs are formed in the spleens from both AA and SS mice. Red arrows indicate B220⁺ B-cell follicles; blue arrows indicate CD3⁺ T cells. T-cell zone is marked in blue. Scale bars, 200 μm.