TLRs are preferentially expressed on human memory B cells. (A) CD19⁺ cells isolated by magnetic sorting were stained with antibodies to CD27 and Ig isotypes. Naive B cells (CD27^-), IgM memory B cells (CD27⁺, IgG^-, IgA^-) and switch memory B cells (IgM^-, IgD^-) were isolated by cell sorting and immediately analyzed for gene expression by PCR (40 cycles). The input cell number of each reverse transcriptase (RT)–PCR reaction is indicated. One representative experiment of 3 is shown. (B) Quantitation of TLR2 (□), TLR4 (▦), TLR7 (▧), and TLR9 (▪) by real-time PCR in naive and memory B-cell subsets. The data are normalized to the expression of β-actin. Data are the mean ± SD of 4 experiments.