Figure 1.

B cells from XBP-1^KO/MD4 mice fail to differentiate into plasma cells. (A, B) XBP-1 deficiency leads to reduced production of plasma cells, whereas all other B-cell compartments of the XBP-1^KO mice appear normal. B cells were isolated from the bone marrow, peritoneal cavity and spleen, and stained with indicated markers. Cells shown were gated on B220⁺ or CD19⁺ populations. The B-cell populations indicated in each panel are as follows: (i) pro-B cells, (ii) pre-B cells, (iii) immature B cells, (iv) pro-B cells, (v) pre-B cells, (vi) immature B cells, (vii) plasma cells, (viii) B-1 cells, (ix) transitional B cells, (x) follicular B cells, (xi) marginal zone B cells, (xii) T-1 transitional B cells, (xiii) T-2 transitional B cells, (xiv) germinal centre B cells and (xv) plasma cells. The numbers indicate the percentages of cells. (C) XBP-1^WT/MD4 and XBP-1^KO/MD4 mice were not immunized. XBP-1^WT and XBP-1^KO mice were repeatedly immunized with HEL. The levels of anti-HEL IgM in the sera were determined by ELISA.