CXCR4 surface expression and signaling are maintained in B220-negative plasma cells. (A) CD5/Mac-1/IgM-depleted cervical lymph node cells were examined by flow cytometry for surface expression of CXCR4 versus B220 and syndecan-1. A representative experiment of 2 is shown. (B) Purified B220-negative plasma cells from E/P^-/- cervical lymph nodes were stimulated with CXCL12 (100 ng/mL) or PMA (10 nM) for the indicated times in unsupplemented RPMI at 37°C, and the presence of phosphorylated ERK1/ERK2 (p44/p42 MAP kinase) was then determined by Western blot as described in “Materials and methods.” Subsequently, the nitrocellulose membrane was stripped and reprobed to determine the presence of total ERK1/ERK2 protein. A representative experiment of 2 is shown.