Biologic properties of interleukin 3. II. Serologic comparison of 20-alpha-SDH-inducing activity, colony-stimulating activity, and WEHI-3 growth factor activity by using an antiserum against IL 3.

An antiserum was prepared against IL 3 and was characterized. Purified Ig from the serum precipitated iodinated IL 3. By using conditioned media from 35S-labeled WEHI-3 cells, a 28,000 dalton protein and a 14/16,000 dalton doublet were specifically immune-precipitated, indicating that the immune Ig reacted with a limited number of WEHI-3-derived proteins. The immune Ig comparably inhibited the ability of purified IL 3 to induce the expression of 20-alpha-SDH, to induce proliferation of the FDC-P1 factor-dependent cell line, or to induce colony formation by bone marrow cells in soft agar. These results support the concept that IL 3 mediates these diverse biologic activities. By using conditioned media from WEHI-3 cells or from an MLR, the immune Ig completely inhibited induction of 20-alpha-SDH or proliferation of FDC-P1 cells, demonstrating that all of the activity is associated with a factor serologically identical to IL 3 purified from WEHI-3-conditioned media. In contrast, the immune Ig did not inhibit bone marrow colony formation by partially purified CSF-2, demonstrating that serologically as well as biochemically, CSF-2 is distinguishable from IL 3. Similarly, the immune Ig did not inhibit IL 2-induced proliferation of a cloned cytotoxic T cell line.