T cell triggering by lectins. I. Requirements for interleukin 2 production; lectin concentration determines the accessory cell dependency.

The requirements for lectin-induced interleukin 2 (IL2) production by human T cells have been investigated. With two different types of T cells, the Jurkat T cell lymphoma and highly purified HLA class II- peripheral T cells, the amount of IL2 produced was strongly dependent on the lectin concentration used. Addition of accessory cells caused a shift in the dose-response curve, resulting in strongly enhanced IL2 production at low concentrations. Thus, the (absolute) accessory cell dependency for T cells to produce IL2 is defined by experimental conditions. Only at lectin concentrations that were found to be optimal in the presence of accessory cells, removal of these cells abrogates IL2 production. Furthermore, after depletion of monocytes IL 2 production by peripheral T cells became almost completely dependent on the presence of thiols in the culture medium. In contrast, the IL2 production by the Jurkat line was not influenced by addition of thiols. The Jurkat model was used to study the nature of accessory cell because this cell line does not show any reactivity to allogeneic cells. Various myeloid and B lymphoid cell lines were tested as accessory cells. The capacity to function as accessory cell was not related to the monocytic origin of the cell. B cell lines were far more effective than monocytes, as two HLA class II- monocytic cell lines were not active. Even after HLA class II determinants were induced on these cells by incubation with an interferon-gamma-containing conditioned medium, they failed to act as as accessory cells. These experiments question the importance of HLA class II molecules and monokines, such as IL1, for lectin-induced IL2 production.