Expression and co-cytokine function of murine thioredoxin/adult T cell leukaemia-derived factor (ADF)

Human ADF (adult T cell leukaemia-derived factor), an isoform of thioredoxin, promotes proliferation of certain human lymphoid cell lines and is involved in many thiol-dependent reducing reactions. To study functional aspects of the murine homologue, we established inducible overexpression of murine ADF in E. coli and a purification method which led to an apparently homogeneous 14 kDa protein. This recombinant ADF was tested in proliferation assays with murine Th2 cells (D10.G4.1) and CTLL-2 cells. In synergy with IL-2, IL-4, IL-7 and IL-9 ADF displayed co-cytokine activity. These proliferative effects were neutralized by an affinity-purified polyclonal rabbit anti-ADF antiserum. The effects of ADF were critically dependent on the presence of 2-mercaptoethanol. Bacterial thioredoxin had similar effects on the proliferation of murine T cells. Thus, the thiol-related reducing capacity of these proteins is essential for their growth promoting activity. As investigated at the levels of mRNA and protein in several murine cell clones and lines as well as in mouse tissues ADF is expressed ubiquitously. Finally it could be demonstrated by competitive PCR that in contrast to cytokine mRNAs (e.g. IL-4 and IL-13) the expression of ADF mRNA in murine Th2 clones and spleen cells is not influenced by stimulation of these cells through the T cell receptor complex. Murine ADF therefore represents a protein constitutively expressed in a wide variety of cells with the capacity to enhance the proliferative effect of several cytokines on murine T cells.