Human B cell-inducing factor(s) for production of IgM, IgG and IgA: independence from IL 2.

Human peripheral blood B cells are stimulated into proliferation by killed Staphylococcus aureus bacteria strain Cowan I (Sac). T lymphocytes in the presence of a T cell mitogen induce high numbers of immunoglobulin-secreting cells (ISC) in these Sac-stimulated B cells. The T cells can be largely replaced by a lymphokine factor. We describe here the 11000-fold purification of this B cell-inducing factor (BIF). BIF preparations that are free of IL 2 do not require IL 2 for optimal induction of ISC. This was shown by the lack of effect of IL 2 alone or with suboptimal or optimal concentrations of BIF on the induction of ISC and by the absence of IL 2 production in the purified B cell population which, with other controls, excludes significant T cell contamination. BIF, purified through four fractionation steps and free of IL 2, induces IgM, IgG, and IgA-ISC in approximately the same ratio as unfractionated lymphokine. Because we have not yet attained a pure BIF preparation, the possibility of separate factors for the production of each immunoglobulin isotype cannot be ruled out.