CHARACTERIZATION OF AN HLA-DR4-RESTRICTED T-CELL CLONE RECOGNIZING A PROTEIN MOIETY OF SMALL NUCLEAR RIBONUCLEOPROTEINS (USNRNP)

In sera of patients with mixed connective tissue disease (MCTD, Sharp Syndrome) high titres of IgG autoantibodies to U1snRNP-specific protei ns are found. The isolated occurrence of these autoantibodies is highl y associated with the HLA-DR4 haplotype. snRNP-specific T cells are su pposed to be involved in this autoantibody production. To address this question we cultured mononuclear cells from MCTD patients and healthy donors with a highly purified UsnRNP preparation from HeLa cells usin g bulk or limiting dilution cultures. Secondary responses to snRNP wer e detected only rarely with T cell lines from two patients and two con trols, and turned out to be unstable during further expansion. One T c ell line derived from a healthy individual retained its snRNP reactivi ty upon limiting dilution cloning and could be characterized in detail . The CD4(+) T cell clone recognized native snRNP particles presented by monocytes in an HLA-DR4 (B10401)-restricted manner. Separation of the protein and RNA moieties of snRNP particles revealed that the T ce ll clone responded specifically to the protein fraction, but not to RN A and diverse control antigens. Sequencing of the T cell receptor alph a and beta chain cDNAs revealed that the clone used the V alpha 14.2 a nd VP beta 14 elements. Upon antigen-specific and mitogenic stimulatio n the T cell clone showed a Thl-specific cytokine pattern, and did not provide helper activity for in vitro Immunoglobulin production. This study demonstrates the presence of self-reactive snRNP-specific T cell s in a healthy donor. The T cell clone may not represent a helper T ce ll for the formation of U1snRNP-specific autoantibodies.