Figure 6.

Responsiveness of cultured bone marrow B cells to BCR ligation. Spleen cells or freshly isolated or cultured (3 days at 2×10⁶/ml) bone marrow cells as indicated, were incubated for 20 hr with IL-4 (100 U/ml), F(ab)₂ anti-µ (10 µg/ml) or anti-CD40 mAb (10 µg/ml) before being analysed for expression of MHC class II by flow cytometry. Analysis was carried out as in Fig. 2. The data shown indicate the fold increase in the mean fluorescence of MHC class II on B220⁺ cells compared to that of control, unstimulated cells. The control values (mean ± SEM) were: spleen, 289 ± 6·4; bone marrow, 135 ± 5·2; cultured bone marrow, 235 ± 4·3. The data shown were calculated from analysis of 5000 gated events in each case. Class II fluorescence on control and stimulated cells was compared by Student’s t-test. Except for responses of freshly isolated cells to IL-4 (*0·5 < P > 0·25) and anti-µ (**0·15 < P > 0·1), all other responses were significantly different from controls (P < 0·0005).