The molecular cloning of interleukins 4, 5 and 6: multifunctional hemopoietic growth factors.

We summarize here our recent studies on the cloning and characterization of three lymphokines which are produced by activated T cells. Interleukins 4, 5 and 6 are involved in the regulation of B cell activation, proliferation and differentiation. IL-4 can activate resting B cells, while IL-5 stimulates the proliferation of activated B cells. Both of these factors also have a role in regulating the isotype of immunoglobulin produced by cultures of D cells. IL-6 appears to induce the differentiation of B cells to secrete high levels of immunoglobulin. In addition, each of these factors is involved in the regulation of other lineages of hemopoietic cells. Thus, T cells control multiple lineages of myeloid and lymphoid cells through the diverse actions of multiple lymphokines. IL-6 is exceptional because it is produced by a variety of cell types, and its action is not restricted to hemopoietic cells.