E-15, a Novel Polysaccharide Mitogen from Nocardia Specific for B Cells

A novel mitogen, E-15, which induced blastogenesis of mouse splenocytes, was purified from the culture filtrate of an actinomycete through ethanol precipitation, anion and cation exchange column chromatography, and gel filtration. The producing organism was identified as Nocar dia asteroides. Spectronic study demonstrated that it was a polysaccharide. Acid hydrolysis of E-15 yielded glucose and glucosamine. The active substance was eluted at the molecular mass between 90 kDa and 750 kDa on gel filtration.E-15 induced a mitogenic response of mouse splenocytes above 1 μg/ml and its potency of induction was superior to a lipopolysaccharide that is known to be a polyclonal B cell-specific mitogen. It showed no toxicity up to 100 μg/ml. The cell surface phenotypes of the blast cells induced by E-15 were analyzed by flow cytometry; they had surface immunoglobulins but no Lyt-2 antigen. Thus it was suggested that E-15 was a B-cell-specific mitogen.