Figure 4.

Soluble CD40 inhibits immunoglobulin production by tonsil B cells activated with CD154. (a) 5 × 10⁴ purified tonsil B cells were cultured with IL-10 (50 ng/ml) and IL-2 (10 IU/ml) in the presence of untransfected L cells or with CD154 transfected L cells with or without 1 µg/ml of purified natural sCD40 or the same sample depleted for sCD40 (only 0·2 µg/ml sCD40 remaining). (b) 4 × 10⁴ irradiated allogeneic PBMC were cultured with 2 × 10⁴ purified tonsil B cells in the presence of IL-10 (50 ng/ml) and IL-2 (10 U/ml) with 1 µg/ml of purified natural sCD40 or the same sample depleted for sCD40 (ΔsCD40, only 0·2 µg/ml sCD40 remaining), or with 5 µg/ml of blocking anti-CD154 mAb or irrelevant control mAb. After 7 days of culture, supernatants were harvested and total immunoglobulin or IgG production was determined by ELISA as described in materials and methods. Results are expressed in mean ± SD of a triplicate culture and is representative of at least three independent experiments.