Characterization of the insulin-like growth factor axis in the human thymus

The components of the insulin-like growth factor (IGF) axis have been inves tigated in the normal human thymus, Using ribonuclease protection assays (R PA), IGF-II transcripts were detected in the normal human thymus, By revers e transcriptase polymerase chain reaction (RT-PCR) analyses, promoters P3 a nd P4 were found to be active in the transcription of IGF2 gene within huma n thymic epithelial cells (TEC), No IGF-II mRNA could be detected in human lymphoid Jurkat T cells with 30 cycles of RT-PCR. By Northern blot analyses , IGFBP-2 to -6 (but not IGFBP-1) were found to be expressed in TEC with a predominance of IGFBP-4. Interestingly, Jurkat T cells only express IGFBP-2 but at high levels. The type 1 IGF receptor was detected in Jurkat T cells but not in human TEC, The identification of the components of the IGF axis within separate compartments of the human thymus adds further evidence for a role of this axis in the control of T-cell development, The precise infl uence of thymic IGF axis upon T-cell differentiation and immunological self -tolerance however needs to be further investigated.