To address the molecular mechanism underlying the functional defects of peripheral T cells in systemic lupus erythematosus (SLE), we focused on early signaling events. We demonstrated that protein expression of the TCR ζ chain was significantly decreased in peripheral T cells from patients with SLE compared to normal controls and patients with systemic sclerosis (SSc). Among those patients showing decreased TCR ζ chain expression, we found two patients with pronounced TCR ζ chain abnormalities, including an aberrant 14 kDa form in one and only trace expression in the other. RT-PCR, SSCP and subsequent cloning of the transcripts revealed that bases 468-503, corresponding to exon 7, were deleted in both patients. Since exon 7 spans the GTP/GDP binding site and N-terminal tyrosine in the third ITAM domain of TCR ζ chain, the transcript lacking exon 7 may be responsible for altered signal transduction via TCR in these SLE patients.
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