IgG1 induction factor.

The IgG1 induction factor elevates the IgG1 response and reduces the IgG2b and IgG3 response in LPS-stimulated spleen cells. The factor is a lymphokine produced by T cells. The precursor frequency for cells secreting the IgG1 induction factor is at least tenfold lower as compared to those secreting interleukin 2. Some biochemical properties of the lymphokine are listed. The effects of gamma interferon in B cell-stimulated cultures are shown. Isolation of a cDNA clone coding for the IgG1 induction factor has been achieved and results of these studies are reviewed. Evidence is given that this lymphokine is the same as B cell stimulating factor 1, and we propose that it be renamed interleukin 4. Finally, the possible mechanisms of interleukin 4 are discussed.