Increased IFN‐α‐induced sensitivity but reduced reactivity of 2′,5′‐oligoadenylate synthetase (2,5AS) in trisomy 21 blood lymphocytes
2,5 AS is induced by interferon‐alpha, ‐beta (IFN‐α, ‐β) and polymerizes adenosine triphosphate (ATP) into pppA (2′ p5′ A) oligomers, leading to inhibition of protein synthesis and virus growth. The gene coding for the IFN‐α, ‐β receptor is localized lo chromosome 21. In trisomy 21 cells from patients with Down's syndrome a 50% increase in gene dosage is present for the genes on this chromosome. Corresponding increase of gene products has been shown for several of these genes, e.g. The IFN‐α, ‐β receptor molecules. Here, we show a direct proportionality between the number of IFN‐α, ‐β receptors and both the basal activity of 2,5AS and the sensitivity of this enzyme for IFN‐α, ‐β. The relative increase of 2,5AS activity (the reactivity) becomes reduced consistent with the increased basal 2,5AS activity in trisomy 21 cells compared with control cells.