T-cell epitopes on the 70-kDa protein of the (U1)RNP complex in autoimmune rheumatologic disorders.
High-titre IgG antibodies against the immunodominant 70-kDa protein of the (U1)ribonucleoprotein (RNP) complex are present in virtually 100% of patients with mixed connective tissue disease (MCTD), and less commonly in a variety of other autoimmune rheumatic diseases. As T-cell 'help' is assumed to be required for this potentially pathogenic form of immune response, investigations to define T-cell epitopes on the 70-kDa protein were undertaken. In prior studies we expressed the 70-kDa protein and a number of its fragments, spanning most of the molecule, as recombinant fusion proteins using the pGEX expression-vector system. These fusion proteins were used as antigens in the epitope mapping studies reported here. PBMC were isolated from patients with (U1)RNP-positive rheumatic diseases and from both normal controls and rheumatologic patients with other autoantibody reactivities, including those to Ro, La and dsDNA. Reactivity to the purified 70-kDa protein was assayed by thymidine incorporation and was evident only in anti-(U1)RNP positive patients but was not restricted to MCTD patients, being present also in patients with SLE and rheumatoid arthritis. The stimulation indices (SIs) observed were in the two- to five-fold range. Using the 70-kDa protein fragments, a T-cell stimulatory epitope was localized to the C-terminal 63 amino acids of the autoantigen. A T-cell line, derived from PBMC of a (U1)RNP positive patient with MCTD, also reacted predominantly with this C-terminal fragment but with an SI of approximately 15-fold. Thus, we have demonstrated the presence and specificity of autoreactive T lymphocytes to a defined peptide epitope in systemic rheumatic disease.
O'Brien
R M
RM
Burnet Clinical Research Unit, Walter and Eliza Hall Institute of Medical Research, Australia.
Cram
D S
DS
Coppel
R L
RL
Harrison
L C
LC
D001172:Arthritis, Rheumatoid / Q000276:immunology; D004306:Dose-Response Relationship, Immunologic; D000939:Epitopes; D006801:Humans; D008180:Lupus Erythematosus, Systemic / Q000276:immunology; D008213:Lymphocyte Activation; D008947:Mixed Connective Tissue Disease / Q000276:immunology*; D011993:Recombinant Fusion Proteins / Q000276:immunology; D012261:Ribonucleoproteins / Q000276:immunology*; D017411:Ribonucleoproteins, Small Nuclear; D012859:Sjogren's Syndrome / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology*
D000939:Epitopes; D011993:Recombinant Fusion Proteins; D012261:Ribonucleoproteins; D017411:Ribonucleoproteins, Small Nuclear