Establishment of a human B cell line that responds specifically to B cell growth factor.

A human B cell line (3D5) that responds specifically to B cell growth factor (BCGF) has been developed by a sequence of Staphylococcus aureus Cowen I activation, EB virus immortalization, and cloning. Proliferative response to PHA-stimulated T cell supernatant (PHA-T-Sup) and nonresponsiveness to rIL-2 stimulation were factors used to screen positive cells. Phenotype analysis with a flow cytometer indicated that: 1) 3D5 is a B cell line: 100% of the cells were positive for B1 marker and 59% were positive for sIg, while T3 and Mo 1 were negative; 2) 3D5 is an activated B cell line: both Tac and 4F2 markers of activated (but not of resting) B cells were 100% positive; 3) 3D5 expresses high molecular weight BCGF (HMW-BCGF) receptor-associated epitope BA5. 3D5 cells proliferated in response to cpBCGF stimulation in a dose-dependent manner. HMW-BCGF also induced 3D5 cells to proliferate. Interestingly, no proliferation could be detected in the presence of rIL-2, rIL-4, or rIFN-r. The data show that 3D5 cells are specifically BCGF-responsive B cells. Using 3D5 cells as target, BCGF activity was detected in crude BCGF preparation sedimented by 85% (NH4)2SO4 and chromatographed in a DEAE-Sephadex A-25 column from PHA-T-Sup. T24 cell supernatant with B cell differentiation factor (BCDF) activity could not induce 3D5 cells to differentiate into immunoglobulin-secreting cells.