T cell epitopes of the La/SSB autoantigen in humanized transgenic mice expressing the HLA class II haplotype DRB1*0301/DQB1*0201.
OBJECTIVE
T cells are implicated in the production of anti-La/SSB and anti-Ro/SSA autoantibodies commonly associated with the DR3/DQ2 haplotype in systemic lupus erythematosus and Sjögren's syndrome. This study was undertaken to investigate the DR3/DQ2-restricted T cell response to wild-type human La (hLa) and a truncated form of mutant La.


METHODS
Humanized transgenic mice expressing HLA-DRB1*0301/DQB1*0201 (DR3/DQ2) were immunized with recombinant antigen and examined for development of autoantibodies and T cell proliferation against overlapping peptides spanning the La autoantigen. HLA restriction and peptide binding of identified T cell epitopes to DR3 or DQ2 were determined using blocking monoclonal antibodies and a direct binding assay.


RESULTS
DR3/DQ2-transgenic mice generated an unusually rapid class-switched humoral response to hLa with characteristic spreading to Ro 52 and Ro 60 proteins following hLa protein immunization. Seven T cell determinants in hLa were restricted to the HLA-DR3/DQ2 haplotype. Six epitopes tested were restricted to HLA-DR and bound DR3 with semiconserved DR3 binding motifs. No DQ restriction of these epitopes was demonstrable despite efficient DQ binding activity in some cases. No neo-T cell epitopes were identified in mutant La; however, T cells primed with mutant La exhibited a striking increase in proliferation to the epitope hLa(151-168) compared with T cells primed with hLa.


CONCLUSIONS
Multiple DR3-restricted epitopes of hLa have been identified. These findings suggest that truncation of La produced by somatic mutation or possibly granzyme B-mediated cleavage alters the immunodominance hierarchy of T cell responsiveness to hLa and may be a factor in the initiation or maintenance of anti-La autoimmunity.
Dudek
Nadine L
NL
Bio21 Molecular Science and Biotechnology Institute, and University of Melbourne, Melbourne, Victoria, Australia.
Maier
Shannon
S
Chen
Zhen-Jun
ZJ
Mudd
Philip A
PA
Mannering
Stuart I
SI
Jackson
David C
DC
Zeng
Weiguang
W
Keech
Catherine L
CL
Hamlin
Kassie
K
Pan
Zi-jian
ZJ
Davis-Schwarz
Karen
K
Workman-Azbill
Jennifer
J
Bachmann
Michael
M
McCluskey
James
J
Farris
A Darise
AD
D000818:Animals; D000974:Antibodies, Antinuclear / Q000096:biosynthesis; D001324:Autoantigens / Q000235:genetics*; D018984:Epitopes, T-Lymphocyte / Q000235:genetics*; D015870:Gene Expression; D006683:HLA-DQ Antigens / Q000096:biosynthesis*; D059866:HLA-DQ beta-Chains; D006684:HLA-DR Antigens / Q000096:biosynthesis*; D059811:HLA-DRB1 Chains; D006239:Haplotypes; D000949:Histocompatibility Antigens Class II / Q000235:genetics* / Q000276:immunology; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D012261:Ribonucleoproteins / Q000235:genetics*; D000097585:SS-B Antigen
D000974:Antibodies, Antinuclear; D001324:Autoantigens; D018984:Epitopes, T-Lymphocyte; D006683:HLA-DQ Antigens; D059866:HLA-DQ beta-Chains; D006684:HLA-DR Antigens; D059811:HLA-DRB1 Chains; D000949:Histocompatibility Antigens Class II; D012261:Ribonucleoproteins; D000097585:SS-B Antigen; C069051:HLA-DQB1 antigen; C553502:HLA-DRB1*03:01 antigen