Purification of immunoglobulin production stimulation factor II alpha derived from Namalwa cells.

An immunoglobulin production stimulating factor (IPSF) in human lymphoblastoid Namalwa cells was purified by the serial use of ammonium sulfate fractionation, hydrophobic interaction chromatography and gel filtration, and named IPSF-II alpha. IPSF-II alpha was estimated as a 112 KD protein composed of a 40 KD polypeptide and two 36 KD polypeptides. The 36 KD protein extracted from SDS-polyacrylamide gel showed IPSF activity, but not the 40 KD protein. The IPSF activity was reasonably stable in alkaline but unstable in acidic solution and heat-unstable. In a serum-free medium, IPSF-II alpha stimulated IgM production of human-human and mouse-mouse hybridomas 4-15 and 2-fold, respectively, although its growth stimulatory effect on hybridomas was negligible. The factor did not stimulate IgG production in either human or mouse hybridomas in the same serum-free medium. These results suggested that IPSF-II alpha was a new cellular factor for stimulating IgM productivity of hybridomas.