Phytohemagglutinin-induced human T-lymphocyte colonies: cellular and T-cell growth factor requirements are the same as for suspension culture growth.

Both T-cell colony formation and T-cell growth in liquid culture requires phytohemagglutinin, either adherent cells or conditioned medium from mononuclear cells, and perhaps other cooperating cells. Despite these similarities, there are some data that the two systems may differ. While it is clear that a source of T-cell growth factor (TCGF) is an absolute requirement for the growth of T cells in liquid culture, less is known of the factors influencing T-cell colony formation. In these studies, production of TCGF during T-cell colony formation was determined. High levels of TCGF can be extracted from methylcellulose when colony formation is rapidly increasing. When colony size is at its maximum, measurable levels of TCGF decline and after 2 weeks little or no TCGF is detectable, suggesting that the factor is used by colony-forming cells. The only requirement for these colony-forming cells to form secondary colonies in replating experiments is exogenous TCGF- The need for adherent cells in primary colony formation can be substantially replaced by interleukin 1, a factor which is produced by adherent cells and functions by amplifying TCGF production. Other promoters of T-cell colony formation may also amplify TCGF production. Addition of dexamethasone to the assay decreases the number and size of the T-cell colonies formed by 75-90%, and colony formation can be completely restored by the addition of purified TCGF. The addition of antigen, lectin, 12-O-tetradecanoyl-phorbol-13-acetate or interleukin 1 cannot overcome the specific dexamethasone-mediated inhibition of colony formation. Although there may be additional requirements for colony formation depending upon the T-cell subset and state of differentiation of the cells, it appears that TCGF is the ultimate proliferative signal in both liquid and colony T-cell growth.