Figure 2.

Immature B cells do not increase their long-term integrin-mediated adhesion response to stimulation, although they have a normal short-term response. (A) Wild-type mature B cells (B con) or immature B cells from Ii^−/− mice (B −/−Ii) were labeled with ⁵¹Cr, washed, resuspended in adhesion medium, and added to fibronectin-coated wells in the presence of PMA, LPS, SDF-1, or IL-2 stimulation. The adherent cells were lysed and radioactivity was determined. One experiment representative of five is depicted. (B) Control B cells were ⁵¹Cr-labeled and tested for adhesion in the presence or absence of PMA, EDTA (5 mM), LDV, or RGD (800 μg/ml). (C) Mature IgD⁺ B cells from control mice (B mature con), immature Ii^−/− B cells (B −/−Ii), and immature IgD⁻ B cells from control mice (B imm con) were ⁵¹Cr-labeled and tested for adhesion. One experiment representative of three is depicted. (D) Cytofluorometric analysis of integrin expression on immature and mature B cells. Control and Ii^−/− splenocytes were double stained with anti-B220 and anti–VLA-4, VLA-5, LFA-1, or α4β7. Histograms show an overlay of the expression levels of the different integrins on control (light) and Ii^−/− (dark) B cells. (E) Resistance to shear stress by mature and immature B cells on fibronectin in a short-term adhesion assay. Control (con) and Ii^−/− (−/−) B cells were allowed to attach to plates coated with fibronectin, alone or coimmobilized with SDF-1 (sdf). After attachment, flow was initiated and increased in 2–2.5-fold increments every 10 s. The number of cells remaining bound at each interval was determined and is expressed as the percentage of input cells remaining bound. The data depict one experiment representative of three.