Human T cell growth factor (TCGF) produced by repeated stimulation of non-adherent human lymphocytes.

T cell growth factor (TCGF) has become a valuable means of maintaining T lymphocytes in long-term culture and of studying T cell function. Numerous problems have been met in the production of TCGF of consistently good quality and in the maintenance of human T cell lines over long periods. We have investigated optimal conditions for TCGF production, and simplified assay systems for TCGF activity. The best TCGF production was obtained by short-term treatment with high concentrations of phytohemagglutinin (PHA). The TCGF producing lymphocytes could be re-used for TCGF production up to 1 month after the first treatment course. Human cultured T cell lines, fresh lymphocytes, short-term PHA stimulated lymphocytes and cultured marmoset T lymphocyte lines were all used for assay of TCGF. We recommend PHA stimulation of human lymphocytes for this assay on a routine basis, comparing results with a standard TCGF batch and calculating a growth index. Adherent cells impair TCGF production. Optimal TCGF production was seen when lymphocyte preparations without adherent cells from different donors were used.

Target selectivity of interferon-induced human killer lymphocytes related to their Fc receptor expression.

Human blood lymphocytes were fractionated on the basis of surface characteristics such as adherence to nylon wool and expression of erythrocyte (E) and Fc receptors. The various subsets were incubated with interferon for 3 hr. Two cell lines that differ in sensitivity to the natural killer effect, K562 and Daudi, were exposed to these lymphocytes (i.e., their sensitivity to interferon-activated killing was tested.) Cell line Daudi, with a low sensitivity to the natural killer effect, was also affected by interferon-activated killing. The efficiency of the nonadherent subsets, separated according to the expression E receptor, ranked similarly in natural killing (anti-K562) and interferon-activated killing (anti-K562 and anti-Daudi) in the following order: E receptor-negative cells, low-affinity E receptor-positive cells, and high-affinity E receptor-positive cells. Further separation on the basis of Fc receptor expression revealed a difference between the two targets. The Fc receptor-positive and -negative cells that did not express high-affinity E receptors killed K562 with similar efficiency whereas Daudi cells were more sensitive to the effect of cells devoid of Fc receptor. Results obtained with other targets suggested that T cell lines behave similarly to K562 and that the difference may be generally valid for T and B cell lines.