NKT-cell help to human B cells is dependent on the presence of apoE. NKT cells and tonsil B cells were cultured in SFM plus αGalCer (200 ng/mL) with or without apoE (2.5 μg/mL). (A) Cells were stained at day 2 and day 4 of culture with anti-CD19 and anti-CD86 antibodies to assess B-cell activation. CD86 expression on CD19⁺-gated B cells cultured together with NKT in media alone (dotted line), αGalCer (solid line), or αGalCer plus apoE (dashed line) on day 2 and day 4 of culture. Unstained cells are shown in solid gray. (B) IgG production by B cells cultured with NKT cells in media alone, αGalCer (200 ng/mL), αGalCer plus apoE. Values are mean ± SEM obtained from 4 individual tonsil samples. *Significant difference (P < .01; analysis of variance).