Characterization of a long-term T-helper-cell line which produces IL-2 and induces immunoglobulin secretion.

Six OKT4+ human T-cell lines that require continuing PHA stimulation and TCGF for continuous growth were established. The cells from all six of these T-cell lines became smaller in size and lost the cell surface Ia antigen when they were grown in phytohemagglutinin (PHA)-depleted growth factor. These cells were unable to survive in the absence of PHA even if exogenous factor was present in great abundance. One of the cell lines (FL) was capable of providing helper functions. In the presence of PHA and phorbol myristate acetate, FL cells produced a growth factor, tentatively identified as Interleukin 2 (IL-2) by its ability to promote the proliferation of an IL-2-dependent murine T-cell line. Moreover, when FL cells were cocultured with B cells, pokeweed mitogen-induced immunoglobulin production was enhanced.