NEW MATERIAL:B cell differentiating factor having the following physical and chemical properties. Molecular weight: 3.5±0.5×10 4 dalton (gel filtration method), 2.2±0.2×10 4 dalton (SDS polyacrylamide gel electrophoresis method). Isoelectric point; pH 4.9-5.1. Specific activity: ≥4.8×10 3 (U/O.D. 280 ).
USE: A remedy for immune deficiency, a culture reagent for normal B cell and a reagent for measuring B cell differentiating factor.
PREPARATION: For example, lymphocyte is separated from human peripheral blood, transformed with human T cell leukemia virus to give human T cell having B cell differentiating factor forming ability, which is cultured, established by limiting dilution method, inoculated into a liquid medium, cultured at 37°C for three days while rotating, a culture mixture is centrifuged, a supernatant liquid is collected, ultafiltered, concentrated and subjected to gel filtration to give B cell differentiating factor.