The Molecular Dimensions of Mitogenic Factor from Guinea Pig Lymph Node Cells

The molecular dimensions of a mitogenic factor from guinea pig lymph node cells were investigated by means of gel filtration, sucrose density gradient ultracentrifugation, and CsCi isopycnic ultracentrifugation. The mitogenic factor was produced by stimulation of immune lymph node cells from inbred guinea pigs, strain 2 or 13, with the specific antigen, ovalbumin; and mitogenic activity was assayed by measuring incorporation of tritiated thymidine by target lymph node cells from syngeneic animals not immune to ovalbumin. The D-20,w of the mitogenic factor was estimated to be (9.9 plus and minus 0.2) times 10-7 cm2/sec by gel filtration on Sephadex G-100, and the apparent S20,w was estimated to be 2.4 plus and minus 0.2 S by sucrose density gradient ultracentrifugation. The buoyant density was determined to be 1.324 plus and minus 0.006 g/ml by CsCi isopycnic ultracentrifugation, and from this value the partial specific volume of mitogenic factor was estimated to be 0.71. From these data the molecular weight of the mitogenic factor was calculated to be 20,000, and the frictional ratio was calculated to be 1.2.