CD45RO enriches for activated, highly mutated human germinal center B cells.

To date, there is no consensus regarding the influence of different CD45 isoforms during peripheral B-cell development. Examining correlations between surface CD45RO expression and various physiologic processes ongoing during the germinal center (GC) reaction, we hypothesized that GC B cells, like T cells, that up-regulate surface RO should progressively acquire phenotypes commonly associated with activated, differentiating lymphocytes. GC B cells (IgD(-)CD38(+)) were subdivided into 3 surface CD45RO fractions: RO(-), RO(+/-), and RO(+).