The purposes of this study were to elucidate the effects of recombinant human interleukin 7 (rhIL-7) on proliferation as well as differentiation of human fetal thymocytes and to analyze the biochemical nature ofthe IL-7 receptorlinked transmembrane signal. In the absence of costimulants, rhIL-7 stimulated the in vitro proliferation and colony formation of CD4+CD8' double-positive immature fetal thymocytes. Furthermore, rhIL-7 promoted partial differentiation of immature thymocytes with a selective advantage for the development of CD4+CD8-single-positive thymocytes. Our observations suggest that IL-7 likely has an important regulatory role during the earliest stages of human T-cell ontogeny. Stimulation of fetal thymocytes with rhIL-7 resulted in enhance tyrosine phosphorylation of three distinct phosphoproteins with molecular masses of 72, 98, 123, and 190 kDa and induced a rapid and biphasic increase in the production of inositol 1,4,5-trisphosphate, which was inhibitable by the tyrosine protein kinase inhibitor genistein. Thus, the transmembrane signal triggered by engagement of the IL-7 receptor is intimately linked to a functional tyrosine protein kinase pathway and stimulates the inositol phospholipid turnover and proliferation, as well as selective differentiation to the CD4 lineage, by human fetal thymocytes.

The V beta chain repertoire in peripheral blood T-cell was analyzed in 23 patients with juvenile rheumatoid arthritis (JRA). Of these, 15 patients had active disease as defined by tender and swollen joints. The ESR was elevated in all but three patients, C-reactive protein (CRP) was elevated in eight. Three patients were investigated during active and inactive phases of the disease. In the active phase of the disease T-cell composition was characterized by an increased number of CD4+ helper cells due to a marked increase in the CD4+CD45RA+ subgroup (34.0 +/- 10.9%, P < 0.001) and a decrease in CD8+CD29+ T-cells (10.3 +/- 5.6%, P < 0.05) compared to controls (15.4 +/- 10.0% and 17.8 +/- 12.3%, respectively). Using the monoclonal antibodies available to determine T-cell receptor (TCR) expression, patients with active disease demonstrated a significant predominance of T-cells bearing TCRs of the V beta 5 family as determined by flow cytometry (7.6 +/- 6.7 vs 3.4 +/- 1.3 in controls, P = 0.01). In active polyarthritis, up to 24% of peripheral blood T-cells expressed TCRs of the same family. In the majority of JRA patients and especially in non-active disease, no preferential TCRs were found compared to controls. However, even defining only a part of TCRs by immunofluorescence, in certain patients a preferential or dominant expression of a single V beta gene family in the T-cells was found, supporting the concept of an involvement of T-cells in the autoimmune pathogenesis of JRA.

117 Downloaded by [University of Otago] at 12:42 27 July 2015 118 F. M. UCKUN et a/.thymic microenvironment. Stimulation of fetal thymocytes with rhIL-3 resulted in enhanced tyrosine phosphorylation of 8 distinct cellular substrates with molecular weights of 44 kDa, 55 kDa, 60 kDa, 69 kDa, 98 kDa, 123 kDa, 150 kDa and 190 kDa, but it did not result in stimulation of phosphoinositide turnover and increased Ins-l,4,5-P3 production. The induction of tyrosine phosphorylation by rhlL-3 was augmented by further crosslinking surface bound IL-3 molecules with an anti-IL-3 antibody and it was abrogated by the tyrosine kinase inhibitor genistein. The ligation of the CD45 protein tyrosine phosphatase markedly suppressed the tyrosine phosphorylation of specific substrates induced by IL-3 stimulation. Thus, the mitogenic transmembrane signal triggered by the engagement of the IL-3 R on human T-cell precursors is linked to a functional protein tyrosine kinase (PTK)/protein tyrosine phosphatase (PTP) regulatory pathway. Taken together, these results indicate that IL-3 may have an important growth regulatory role in early stages of human T-cell ontogeny. KEY WORDS:Interleukin 3 Tyrosine phosphorylation proliferative activity foetal lymphocytes leukemic T-precursors T-cell ontogeny