The purification and properties of human T cell growth factor

Human T cell growth factor (TCGF) has been purified more than 800-fold from serum-free lymphocyte conditioned media by utilizing ion exchange chromatography with DEAE-Sepharose, gel filtration with Ultrogel AcA54, and preparative SDS-polyacrylamide gel electrophoresis. This mitogenic protein, which is released by T cells into the incubating media after exposure to a lectin (PHA), has a m.w. of 13,000 as determined by SDS-PAGE and 20,000 to 25,000 on gel filtration and has an isoelectric point of 6.8. The material extracted from acrylamide gels is a single band (or two nearly superimposed bands) when rerun on analytical SDS gels. Partially purified material is unstable even at -70 degrees C and requires the addition of bovine serum albumin or polyethylene glycol to maintain biologic activity. It is sensitive to proteolytic digestion but resistant to nucleases and thiol-reducing agents such as dithiothreitol. Human TCGF can be reversibly denatured with urea or SDS. Material extracted from acrylamide gels has been shown to sustain T lymphoblasts in tissue culture. In contrast to lectins, certain antigens, and crude lymphocyte conditioned media, purified TCGF does not initiate lymphocyte blastogenesis but is a highly selective mitogen for T cells previously activated by exposure to lectins or antigens.