Immunological evidence for the relation between low MR secreted form of human B cell growth factor and an...

Homogeneously purified intracellular high-Mr BCGF (IC-BCGF) has been used as an immunogen for the development of heterotypic anti-IC-BCGF antibodies. Anti-IC-BCGF immunoglobulin has been purified by affinity chromatography and used for constructing an immunoaffinity matrix. This matrix was shown to recognize specifically IC-BCGF and the extracellular low-Mr secreted form of human BCGF (EC-BCGF). In the cytosolic extracts of lectin activated human PBLs two other proteins of 50K and 30K were also recognized by these antibodies. Immuno dot blot and western blot analysis also demonstrated that anti-IC-BCGF antibodies recognized EC-BCGF. These antibodies weakly interacted with human interferons (alpha, gamma). Immunoaffinity-purified IC-BCGF was shown to have a molecular weight of 60K, and it exhibited BCGF activity in long-term BCGF-dependent B cell lines. The Mr of one-step affinity-purified EC-BCGF was found to be 14K by SDS-PAGE analysis. This material demonstrated BCGF activity in both long-term BCGF-dependent B cell lines and anti-IgM-activated GoB cells, yet it did not exhibit IL-1 and IL-2 activities. We conclude that EC-BCGF is immunologically related to IC-BCGF through common structural epitopes.