Clinical Data Patients Initial disease Outcome Sex Age * yr Acquired IgA - D patients BEAU Reflux

We have previously shown that human B lymphocytes cultured in the CD40 system, composed of an anti-CD40 mAb presented by a CD32-transfected fibroblastic cell line, proliferate but do not secrete antibodies. However, the addition of particles of Staphylococcus aureus Cowan (SAC) induces B cell differentiation even in the absence of exogeneous cytokines (CD40/SAC system). Additionally, B lymphocytes cultured in the CD40 system in the presence of human IL10, produce IgM, IgG, and IgA, and Ig levels are further increased by SAC. Here, we have studied the capacity of peripheral blood lymphocytes from patients with IgA deficiency (IgA-D) to secrete Igs, particularly IgA after CD40 triggering. Peripheral blood mononuclear cells (PBMNC) from IgA-D patients cultured in the CD40/SAC system produced IgM and IgG, but not IgA. The addition of IL-10 to the cultures, enhanced the production of IgM and IgG and most strikingly induced the production of high amounts of IgA. The addition of IL-10 to PBMNC from IgA-D patients activated through CD40 alone resulted in the production of IgA. Thus, SAC and anti-CD40 mAb stimulate B cells to differentiate into cells secreting IgG and IgM whereas IL10 plays a central role in inducing B cells from IgA-D patients to differentiate into IgA secreting cells. (J. Clin. Invest. 1994. 94:97-104.)