Fig. 2.

Promotion of IgE and IgG production by CD4⁺ T lymphocytes in response to α-galactosylceramide (α-GC)-loaded B cells is mediated by invariant natural killer T (iNK T) cells. Purified CD4⁺ lymphocyte fractions (15 × 10⁴ cells) were co-cultured in interleukin (IL)-2-containing medium with 5 × 10⁴ α-GC-loaded B cells (a,b) or with 5 × 10⁴ B cells and the TSST1 superantigen (c). Supernatant concentrations of IgG and IgE were determined as above. Data are means ± s.e.m. from four to six wells (one typical experiment of three). (a) CD1d-dependence of the CD4⁺/α-GC-loaded B cell cooperation in Ig production. Blocking anti-CD1d monoclonal antibody (20 µg/ml) was added or not to α-GC-loaded B cells before co-culture. (b) Vα24-depleted CD4⁺ lymphocytes fail to help B cells to produce Ig. Depletion of Vα24⁺ cells from CD4⁺ cells was achieved by magnetic cell sorting. (c) CD4⁺ lymphocytes activated by the TSST1 superantigen do not help B cells to produce Ig.