ACTIVATION-DEPENDENT EXPRESSION OF THE INSULIN-LIKE-GROWTH-FACTOR BINDING PROTEIN-2 IN HUMAN-LYMPHOCYTES

The expression of the insulin-like growth factor binding protein-2 (IG FBP-2) was assayed in mononuclear cells originating from different org ans of the immune system. All mononuclear cells studied did express IG FBP-2, but the expression level was found to be dependent on the cell type and origin of the cell. T cells showed a higher expression of IGF BP-2 mRNA than did B cells, and CD34(+) stem cells expressed IGFBP-2 m RNA at a high level. Expression was highest in bone marrow and thymus. Stimulation of peripheral mononuclear cells resulted in a marked incr ease of IGFBP-2 mRNA and also intracellular IGFBP-2, as analysed by fl uorescence staining. This increase parallels the increase of other kno wn T-cell activation markers. Furthermore, the increase of intracellul ar IGFBP-2 seems to precede T-cell blast formation and all T cells in active phases of the cell cycle have high levels of IGFBP-2. Our resul ts provide a basis for further investigations on the contribution of t he IGF-system to the regulation of T-cell proliferation and differenti ation. IGFBP-2, in particular, may have an important influence in the regulation of T-cell activation and proliferation.