Recombinant Human IL-5 Augments Immunoglobulin Generation by Human B Lymphocytes in the Presence of IL-2

The biological activity of interleukin-5 (IL-5) on human B lymphocytes was examined by using a newly purified recombinant human IL-5 preparation. Different densities of B cells from human tonsil samples were isolated by Percoll density gradient from nonrosetted cells. The IL-5 preparation did not act as a B cell growth factor on the large (in vivo-activated) or small (resting) B cells after activation with polyclonal B cell activators. The IL-5 augmented the immunoglobulin (Ig) generation of Staphylococcus aureus Cowan strain I (SAC)-activated B blasts in the presence of interleukin-2 (IL-2). The effect of IL-5 on Ig generation was greater in pokeweed mitogen (PWM)-driven B blasts than that in SAC-induced B blasts when assessed by enzyme-linked immunosorbent assay. The amounts of μmRNA isolated from IL-5/PWM-treated cells were also larger than those from IL-5/IL-2-treated B blasts. These results suggest that the human IL-5 can increase Ig generation of B cells in the presence of IL-2 by working at the level of mRNA coding for Ig.