NEW MATERIAL:A lymphokine produced by human B cell, a human B cell differentiation factor (BCDF) having the following properties. Molecular weight: 15,000W30,000. Isoelectric point: 5W5.5. Heat stability: ≥90% human B cell differentiation factor activity remains by treatment at about neutrality at 50°C for 30min (≥90% activity disappears by treatment at 80°C for 15min). pH Stability: ≥90% activity remains by treatment at 25°C at 2pH for 30min. Trypsin treatment: activity is reduced.

USE: BCDF antibody is prepared from BCDF, and used for immunological pathological analysis by the use of immunoassay. BCDF is useful for remedy and diagnosis of various diseases, for example, it is administered to a patient of immune incompetence so that mechanism of antibody production is restored to a normal state.

PREPARATION: Lymphocyte is separated from human peripheral blood or amygdala by density-gradient centrifugation, etc., human B cell is transformed by the use of EVB, a cell strain B of BCDF preparation is established, and it is cultivated to obtain human BCDF.