Defective Calcium‐Dependent Signal Transduction in T Lymphocytes of Ataxia‐Telangiectasia

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Abstract
T‐cell functions of two patients with ataxia‐telangiectasia were investigated. Patients with ataxia‐telangiectasia had reduced percentages of circulating CD3+ cells and CD4+ cells, although neither patient had a reduced percentage of circulating CD8+ cells. The proliferative responses and interleukin‐2 production of peripheral blood mononuclear cells to T‐cell mitogens were reduced in the patients. The intracellular calcium concentration in T cells or CD4+ cells from both patients was only slightly increased after phytohaemagglutinin stimulation. Moreover, the concentration after OKT3 stimulation was not or only slightly increased in T cells or CD4+ cells from both patients. Our results suggest that the functional defect of T cells is caused by defective Ca2+‐dependent signal transduction through the CD3 complex of the surface in T cells of ataxia‐telangiectasia.