T-CELL LINES RECOGNIZING THE 70-KD PROTEIN OF U1 SMALL NUCLEAR RIBONUCLEOPROTEIN (U1SNRNP)

In sera of patients with mixed connective tissue disease (MCTD) high t itres of IgG autoantibodies to U1snRNP-specific proteins (70 kD, 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 h ealthy donors with a highly purified UsnRNP preparation from HeLa cell s. Nine T cell lines were established by limiting dilution cloning fro m two MCTD patients and five T cell lines from a healthy individual. A ll T cell lines expressed the TCR alpha beta/CD3 complex. Surprisingly , most of the T cell lines exhibited the CD8 phenotype. Irrespective o f this phenotype, all T cell lines showed a proliferative response to an N-terminal part (aa 51-195) of recombinant U1-specific 70-kD protei n. One CD8(+) T cell clone exhibited cytotoxic activity against an aut ologous B cell line pulsed with snRNP or recombinant fragments (aa 51- 195 and aa 51-88). Interestingly, two T cell lines proliferated in res ponse to four recombinant polypeptides representing different parts of the U1snRNP 70-kD protein. Since regions of sequence homology are dis tributed over the 70-kD molecule, it is suggested that conserved motif s may be recognized by the T cell lines.