| Research Abstract |
BAFF is a member of the tumor necrosis factor (TNF) ligand family and co-activates B cells in vitro and in vivo-. BAFF-BAFF receptor system has a key role in the pathogenesis of the lupus-like disease in mice. In human, serum concentration of BAFF in SLE patients had been shown to be elevated compared with that in normal healthy controls. However, the mechanism of elevated serum BAFF in SLE patients has not been fully elucidated. To explore the mechanism, we attempt to examine mRNA level of BAFF in SLE patients.
BAFF open reading frame cDNA was amplified by RT-PCR from PBL of SLE patients and healthy controls. Aliquots were taken from the reaction mixture every three cycles, starting with cycle 21. After electrophoresis in an agarose gels with ethidium bromide, UV-induced fluorescence of specific bands was quantitated as relative O.D. values. We calculated the difference in the number of cycles (Δn) needed to reach identical-yields of specific PCR products as compared to the internal G3
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PDH standard. We then compared BAFF mRNA expression levels with clinical manifestations and laboratory findings in SLE patients. The experiments showed that BAFF mRNA was upregulated in SLE PBL, and it was closely associated with the increased level of serum anti-dsDNA antibody, but not serum immunoglobulin nor complement concentration, suggesting that BAFF has an important role in overproduction of autoantibody in SLE.
In the earlier studies, we demonstrated the defective expression of TCR z chain in more than half of the patients with SLE. Since the defects appear to be central in dysfunction of SLE T cells, we, next attempt to investigate the molecular mechanism of BAFF expression, particularly focusing on its relationship to aberrant expression of TCR z. Chain. We constructed the mammalian expression vector containing two spliced variants form of TCR z chain, which are exclusively observed in SLE. We transfected these vectors into mouse T cell hybridoma, designated MA5.2, which lacks TCR z chain, and established stable transfectants expressing two spliced variants such as short 3' UTR and exon 7(-). Not only surface expression, but also cytoplasmic expression of TCR z chain was significantly downregulated in the two transfectants. MRNA stability assay clearly demonstrated that the downregulated expression of TCR z chain in the transfectants is resulted from the unstable mRNSA for both short 3'UTR and exon 7(-) variants. Microarray analysis showed that a series of mRNA are upregulated and downregulated in these two transfectants, when compared to MA5.2 transfected with wild form TCR z chain. The experiment showing that the mRNA of BAFF was not changed in the two TCR z variants, raises a possibility that increased BAFF expression observed in SLE T cells is independent abnormality, but not secondary to TCR z defect in SLE. Less
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