Induction of immunoglobulin mu mRNA in a B cell transfectant stimulated with interleukin-5 and a T-dependent antigen.

We have established an Ag-specific in vitro system for studying the roles of Ag and IL-5 in B cell differentiation and Ig production. The murine B cell leukemia, BCL1B1, was transfected with mu and kappa genomic sequences and VS107 V regions that conferred a T15 Id and phosphocholine-binding specificity upon the cells. Transfected cells were treated with both the T-dependent Ag phosphorylcholine-key-hole limpet hemocyanin (PC-KLH), and 0.5 ng/ml purified IL-5. After 3.5 days steady state mu-mRNA levels increased three- to fourfold over mu-mRNA levels obtained from untreated cultures, or cultures treated with IL-5 or PC-KLH alone. IL-5 alone caused increased Ig secretion and a nearly twofold increase in proliferation. Additionally, cells treated with PC-KLH alone were able to process the Ag and present it to T cells as shown by subsequent lymphokine production. Thus, both Ag and IL-5 used singly appear to interact with their respective receptors, although neither Ag nor IL-5 increased mu-mRNA levels when used singly. The production of increased mu-mRNA levels obtained with Ag plus IL-5 required polymerase II transcription, suggesting that they may act to increase Ig transcription directly.