Analysis of the regulation of expression of CB2 receptors during B-cell differentiation. Human tonsillar B-cell subsets were analyzed by flow cytometry (□) and by RT-PCR (▪) to quantitate CB2 receptor expression at the protein and transcript levels, respectively. For flow cytometric study, phenotypes of virgin B cells (IgD⁺ CD38⁻), GC B cells (IgD⁻ CD38⁺), centroblasts (IgD⁻ CD77⁺), and memory B cells (IgD⁻ CD38⁻ CD44⁺) were performed on tonsillar B cells as indicated in Materials and Methods. Results are the mean ± SD from three different donors and were calculated as described in Fig 3. For RT-PCR, the level of mRNA in each subset was quantitated from 2 × 10⁵ virgin B cells, GC B cells, centroblasts, or memory B cells sorted by FACS. CB2-receptor mRNA contents were normalized with that of β₂-microglobulin and are expressed in arbitrary units. This experiment was repeated from two different donors with similar results.