This paper reports on differences between B cell-type chronic lymphocytic leukaemia (B-CLL) and normal B cells in their response to IL-2+thioredoxin (Trx), Staphylococcus aureus Cowan strain 1 (SAC)+IL-2+Trx, and to CD40 ligation of IL-2+Trx and SAC+IL-2+Trx stimulation. The authors found that Trx acted synergistically with IL-2 and SAC+IL-2 in inducing DNA synthesis in B-CLL cells, but not in the normal B cells. Interestingly, IL-2+Trx alone was found to induce proliferation in B-CLL cells from patients with advanced stages of disease. In addition, we also found that IL-2+Trx and SAC+IL-2+Trx-induced DNA synthesis of B-CLL cells was inhibited by CD40 activation (by soluble anti-CD40 MoAb and anti-CD40 MoAb presented on irradiated CD32L cells). In clear contrast, SAC+IL-2+ Trx-induced DNA synthesis of normal B cells was not inhibited by soluble anti-CD40 MoAb. The authors therefore conclude that B-CLL cells differ from normal B cells in their response to IL-2 (IL-2+Trx) and CD40 ligation.