Establishment of an IL-12-responsive T cell clone: Its characterization and utilization in the quantitation of IL-12 activity

We previously demonstrated that proliferation of terminally differentiated Thl clones depends primarily on an interleukin-12 (IL-12)-paracrine mechanism mediated by their interactions with antigen-presenting cells (APC) rather than on an IL-a-autocrine mechanism, Such a Thl clone (4-86, C57BL/6 origin) was cultured with recombinant IL-12 (rIL-12) in the absence of either antigen or APC, Some cells survived for several passages of culture with only rIL-12, and by limiting dilution, several clones highly reactive to rIL-18 alone were obtained, One of these clones, designated 2D6, was found to proliferate strongly in response to less than 1 pg/mL of rIL-12, This clone exhibited the following surface phenotypes: CD3(+), T cell receptor (TCR) alpha beta(+), v beta 11(+), NK-1.1(-); CD4(-) CD8(-); LFA-1(+), ICAM-1(+); and CD28(+), CD80(+), CD86(+), CTLA-4(-). In accordance with high responsiveness to IL-12, 2D6 cells were also found to express IL-12 receptor (IL-12R) as detected by incubation with rIL-12 and then staining with anti-IL-12 monoclonal antibody (mAb), Stimulation of 2D6 with rIL-12 resulted in the expression of interferon-gamma (IFN-gamma) and IL-10 mRNAs and production of these cytokines, The 2D6 clone responded to IL-2 (vigorously), IL-7 (moderately), and IL-4 (mildly) in addition to IL-12, However, the Ab capture assay using anti-IL-12 mAb enabled us to quantify IL-12-specific activity contained in a given sample, Thus, this study describes the unique features of the IL-13-responsive T cell clone and demonstrates the utilization of this clone in the quantitation of a specific IL-12 activity.