FIGURE 2. Absence of primary follicles and FDCs in BLC^-/- mice, and defective homing of CXCR5^-/- B cells to lymph node follicles.

a, BLC^+/- and ^-/- spleen and lymph nodes stained for the indicated markers. Labels are in the same colour as the reaction product for that marker. Follicular B cells are mostly IgD ^hiIgM^lo and appear brown, whereas marginal zone B cells are mostly IgD^loIgM^hi and appear blue (top panels). Boundaries of the marginal zone are indicated by brackets. b, BLC ^+/- and ^-/- spleen and lymph nodes stained to detect CR1 and T cells. FDCs appear as a network of intense staining for CR1, whereas splenic CR1^hi marginal zone B cells appear as a rim of faintly stained cells. Spleen and lymph nodes of more than 20 BLC^+/- and ^-/- mice were analysed for follicular organization. c, Wild-type (WT) lymph node stained to detect BLC and B cells. Inset, adjacent section stained to detect T cells. d, High magnification view of a wild-type lymph node follicle stained to detect BLC and FDC (CR1). Arrows indicate examples of BLC and CR1 double-positive cells. Data are representative of four independent experiments. e, f, Distribution of transferred wild-type (e) or CXCR5^-/- (f) CFSE-labelled B cells in lymph nodes of wild-type recipients. Sections were stained to detect endogenous B cells and FDCs. Data are representative of four recipients. F, follicle; T, T zone; B*, BLC- and FDC-deficient area rich in B cells.