Fig. 3.

NF B cells express laminin α5 binding integrins and show some colocalization with laminin α5 in the MZ. (A) Representative flow cytometry for cell surface integrin expression on NF B cells with antibody isotype controls shown in gray. (B) In vitro adhesion of MZ, FO, and NF B cells to VCAM-1, laminin 511/521, the RGD-containing laminin α5 domain IVa, agrin, fibronectin (all 30 μM), or BSA. Adhesion of NF B cells to VCAM-1, laminin 511/521, or fibronectin was measured in the presence or absence of function blocking antibodies to integrins β1 (Ha2/5), α6 (GoH3), or α4 (PS/2). Data shown are mean values ± SEM from three separate experiments with n = 6 for each treatment in each experiment. (C) Immunofluorescence staining shows the presence of IgM⁺CD21^low and (D) IgM⁺AA4.1⁺ B cells in the MZ of mature mice (arrowheads). Magnification, 100× (D, Left), 200× (C, Upper), 400× (C, Lower, and D, Right). (E) In vivo localization of ex vivo TAMRA-labeled NF B cells or FO B cells (isolated from day 10 mouse spleens) at 16 h after i.v injection into mature mice in the presence or absence of GoH3. Immunofluorescent staining for laminin α5 reveals localization of NF B cells in the MZ (double arrows), follicle, and RP, whereas FO B cells home predominantly to the follicle. Coinjection with GoH3 reduced TAMRA⁺ NF B-cell localization to the MZ only. Magnification: 100×. Bar graph shows quantification of the ratio of MZ/FO localized TAMRA⁺ cells; data are means ± SEM from two experiments with four mice in each category. *P < 0.05; **P < 0.01.