Fig. 1.

IgE and IgG production by α-galactosylceramide (α-GC)-loaded B cells is enhanced by CD4⁺ T lymphocytes but not by their double-negative (DN) counterpart. Purified CD4⁺ or DN lymphocyte fractions (15 × 10⁴ cells) were co-cultured in medium containing interleukin (IL)-2 with 5 × 10⁴ B cells either non-loaded or loaded with α-GC. (a) Similar fold expansion of DN invariant natural killer T (iNK T) cells and CD4⁺ iNK T cells in response to α-GC-loaded B cells. Expansion was calculated after a 7-day culture by dividing the number of Vα24-positive T cells in co-cultures with α-GC-loaded B cells by their number in co-cultures with non-loaded B cells. The total number of iNK T cells recovered ranged from 0·75 × 10³−25·7 × 10³ cells/well for CD4⁺ fraction (n = 4) and from 0·8 × 10³ to 17·5 × 10³ cells/well for their DN counterpart (n = 4), depending on their frequency in fresh peripheral blood lymphocytes (which varied considerably between individuals). Data are mean values ± s.e.m. of experiments performed with PBL obtained from four healthy donors. (b) CD4⁺ lymphocytes promote Ig production by α-GC-loaded B cells. Concentrations of IgM, IgG and IgE in supernatants were determined after a 12-day culture. Data are from experiments performed with cells from four to six healthy donors, each symbol corresponding to one donor; significant differences (P < 0·02 and P < 0·03, respectively, according to Wilcoxon's test) were found for IgE and IgG only. (c) Comparison of IgE levels in supernatants of B cells co-cultured with CD4⁺ or DN cells in the presence or absence of α-GC. Data are means ± s.e.m. from one typical experiment of three.