Figure 7.

XBP-1-deficient plasma cells mount only a short lived but robust antibody response due to their failure to colonize into the bone marrow. (A) XBP-1^WT/MD4/Blimp-1-GFP and XBP-1^KO/MD4/Blimp-1-GFP mice were immunized with HEL at the following time points: days −34, −20 and −7 (3 × immunized); days −20 and −7 (2 × immunized); day −7 (1 × immunized); or unimmunized (0 × immunized). Splenocytes and bone marrow cells from all these mice were isolated on the same day (day 0), stained for CD138 and analysed by flow cytometry. The percentage of Blimp-1-GFP-positive/CD138-positive cells is indicated in the upper right quadrants. The results are representative of two independent experiments. Note that very few cells (0.05 and 0.09%) in the bone marrow of XBP-1^KO/MD4/Blimp-1-GFP mice are Blimp-1-GFP-positve and CD138-positive after reimmunization. (B) The percentages of CD138+/Blimp-1-GFP+ B cells from the spleens and bone marrow of immunized mice (shown in A) were plotted. (C) HEL-specific antibody titers in the sera from mice described in (A) were measured by ELISA. (D) Day 4 LPS-stimulated XBP-1^WT/MD4 and XBP-1^KO/MD4 plasmablasts were stimulated with CXCL12 for indicated time and lysed immediately. Lysates were immunoblotted for phospho-ERK1/2, ERK1/2 and actin.