Activation‐dependent expression of the insulin‐like growth factor binding protein‐2 in human lymphocytes

Abstract

The expression of the insulin‐like growth factor binding protein‐2 (IGFBP‐2) was assayed in mononuclear cells originating from different organs of the immune system. All mononuclear cells studied did express IGFBP‐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 IGFBP‐2 mRNA than did B cells, and CD34 + stem cells expressed IGFBP‐2 mRNA at a high level. Expression was highest in bone marrow and thymus. Stimulation of peripheral mononuclear cells resulted in a marked increase of IGFBP‐2 mRNA and also intracellular IGFBP‐2, as analysed by fluorescence staining. This increase parallels the increase of other known T‐cell activation markers. Furthermore, the increase of intracellular 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 results provide a basis for further investigations on the contribution of the IGF‐system to the regulation of T‐cell proliferation and differentiation. IGFBP‐2, in particular, may have an important influence in the regulation of T‐cell activation and proliferation. A 23187, calcium ionophore IGF I/II, insulin‐like growth factor‐I/II IGFBPs, insulin‐like growth factor binding proteins PBMC, peripheral blood mononuclear cell MNC, mononuclear cell MACS, magnetic‐activated cell sorting GAPDH, glycerinaldehydphosphate RT‐PCR, reverse transcriptase–polymerase chain reaction.