Biochemical characterization and purification of human B cell stimulatory factor (BSF)

B cell stimulatory factor (BSF)1 activity was generated over a period of five days by phytohemagglutinin - stimulated E rosette - positive peripheral blood lymphocytes. This activity was subjected to a multistep purification procedure including ammonium sulfate precipitation, anion-exchange chromatography, gel filtration, procion redagarose chromatography and reverse phase high performance liquid chromatography (RP-HPLC). The last purification step dissected BSF activity into two active fractions, one corresponded to the interleukin 2 (IL2) activity whereas the other active fraction was free of IL2 activity. Preparative isoelectric focusing analysis defined isoelectric points of pH 7.2 for both BSF and IL2. Molecular weight analysis of BSF was carried out by preparative sodium dodecyl sulfate - polyacrylamide gel elec- trophoresis analysis. BSF activity was eluted from gel strips corresponding to a molecular mass of 16 and 17 kDa. The 16-kDa fraction was free of IL2 activity wher eas the 17-kDa fraction overlapped with IL2. Since recombinant IL2 was capable of exhibiting significant BSF activity in anti-IgM or Staphylococcus aureus Cowan strain I-dependent assay systems, it cannot be excluded that IL2 itself is a BSF. Nevertheless these studies demonstrate the existence of a BSF free of IL 2 activity.