Functional interaction between interleukin-9/P40 and interleukin-4 in the induction of IgE production by normal human...

Interleukin-4 (IL-4) has been shown to induce a high rate of IgE production by normal B lymphocytes from peripheral blood without preactivation of these cells. In the present study, significant IgE production was observed at the concentration of 30 U/mL IL-4 (0.5 ng IgE/mL), and a plateau value was reached at 300 U/mL (1.2 ng IgE/mL). In these experiments, recombinant human (rh) and murine (rm) interleukin-9/P40 (IL-9/P40) were unable to induce such an IgE production by human B lymphocytes. However, in the presence of a suboptimal dose of IL-4 (100 U/mL), both rh and rm IL-9/P40 enhanced the IgE production in a dose-dependent manner (from 3 to 1000 U/mL). Under these experimental conditions, the slight but significant (p < 0.01, Student's t test) production of IgG (50 ng/mL) was also potentiated when the cell cultures were performed in the presence of 300 U/mL of IL-9/P40. The IL-4-induced IgG and IgM production by purified B lymphocytes preactivated with Staphylococcus aureus Cowan strain I was also potentiated in the presence of 300 U/mL of rh IL-9/P40, indicating a direct effect of this cytokine on this cell type. In contrast, IgE production by Staphylococcus aureus Cowan strain I-activated B lymphocytes was never observed. Taken together these data suggested a direct role for IL-9/P40 in the regulation of immunoglobulin production by B lymphocytes.