Figure 3

CD11b⁺ B1 cells suppress naive CD4⁺ T-cell activation. Sort-purified naive (CD20⁺ CD27⁻CD43⁻) (N) and memory (CD20⁺CD27⁺CD43⁻) (M) B cells, and CD11b⁻ (CD20⁺ CD27⁺CD43⁺CD11b⁻) (11b⁻) and CD11b⁺ (CD20⁺CD27⁺CD43⁺CD11b⁺) (11b⁺) B1 cells, were cocultured 1:1 with negatively selected naive CD4⁺ T cells plus plate-bound anti-CD3. Control cultures contained T cells with soluble anti-CD28 in addition to anti-CD3 but no B cells (+) and T cells with no antibody and no B cells (−). T-cell activation was assessed by staining for surface CD4 and intracellular TNF-α. (A, B) The fraction of CD4⁺T cells expressing TNF-α after 3 d culture is shown for a representative experiment in (A) and for three independent experiments in (B). Vertical bars in (B) represent mean values, and lines indicate SEM. The cutoff for intracellular TNF-α positivity was determined on the basis of fluorescence-minus-one.