Cellular composition of lymphoid aggregates in the stomach mucosa of CCR7^−/− mice. (A) The cellular composition of aggregated structures was assessed by immunohistochemical staining of paraffin or frozen sections. Consecutive sections were stained in red with antibodies against CD3, CD4, CD8, B220, FDC (indicated by an arrow), PNAd (indicated by an arrow), BrdU (indicated by an arrow), CCL21, or CXCL13. Original magnification, ×200 (with the exception of anti-BrdU, ×100). Representative sections are shown (> 60 sections obtained from 6 mice). (B) Frozen sections of aggregated structures were stained with anti-B220 (in green) and anti-CD3 (in red), and with anti-CD11c antibody (in red or green as indicated; representative CD11c⁺ cells are indicated by an arrow). Original magnification, ×200. Representative sections for each age group are shown (n = 3 mice for each group).