Purification to homogeneity of a high molecular weight human B cell growth factor; demonstration of specific binding to activated B cells; and development of a monoclonal antibody to the factor

High molecular weight B cell growth factor (HMW-BCGF) produced by a T cell line was purified to homogeneity and demonstrated to bind specifically to activated human B cells. A monoclonal antibody to HMW- BCGF was developed that (a) specifically inhibited the activity of HMW- BCGF in enhancing B cell proliferation, (b) specifically bound to HMW- BCGF in Western blots, (c) specifically absorbed HMW-BCGF activity from culture supernatants, and (d) specifically absorbed an internally labeled protein from T-ALL supernatant which comigrates with HMW-BCGF on sodium dodecyl sulfate-polyacrylamide gels. This antibody should help in cloning the gene for HMW-BCGF and further exploring the physiologic roles of HMW-BCGF.