Partial purification and characterization of a BCGFII from EL4 culture supernatants.

Two B cell growth factor activities have been previously described. One activity, present in the culture supernatants of PMA-induced EL4 is active in a co-stimulator assay with normal B cells and anti-immunoglobulin. The other activity is present in the culture supernatants of the alloreactive T cell line C.C3.11.75 and can be assayed in a co-stimulator assay with normal B cells and dextran sulfate or with BCL1 in vivo line B cell tumor. We have termed the first activity BCGFI and the second BCGFII. We have now shown that a very similar BCGFII activity can be obtained from EL4 culture supernatants induced by PMA. This (EL4)BCGFII has an apparent m.w. of 55,000, is eluted from DEAE Sephacel at 0.05 M NaCl, and has a pI of 5.5, which is clearly distinct from the properties of (EL4)BCGFI activity. (EL4)BCGFII activity is similar to but not identical to (DL)BCGFII. It differs from (DL)BCGFII in chromatographic behavior and in the kinetics of the response of BCL1 to the two factors. (EL4)BCGFII activity can be detected in 18 to 24 hr by virtue of its ability to cause in vitro proliferation of in vivo BCL1 tumor B cells.