T cell lines recognizing the 70-kD protein of U1 small nuclear ribonucleoprotein (U1snRNP)

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Abstract
SUMMARY: In sera of patients with mixed connective tissue disease (MCTD) high titres of IgG autoantibodies to U1snRNP-specific proteins (70kD, A, C) are found, suggesting an antigen-driven and T cell-dependent process. In order to establish U1snRNP-specific T cell lines we cultured under various culture conditions mononuclear cells from MCTD patients and healthy donors with a highly purified UsnRNP preparation from HeLa cells. Nine T cell lines were established by limiting dilution cloning from two MCTD patients and five T cell lines from a healthy individual. All T cell lines expressed the TCRαβ/CD3 complex. Surprisingly, most of the T cell lines exhibited the CD8 phenotype. Irrespective of this phenotype, all T cell lines showed a proliferative response to an N-terminal pan (aa 51–195) of recombinant U1-specific 70-kD protein. One CD8+ T cell clone exhibited cytotoxic activity against an autologous B cell line pulsed with snRNP or recombinant fragments (aa 51–195 and aa 51–88). Interestingly, two T cell lines proliferated in response to four recombinant polypeptides representing different parts of the U1snRNP 70-kD protein. Since regions of sequence homology are distributed over the 70-kD molecule, it is suggested that conserved motifs may be recognized by the T cell lines.