Reactivity with dichotomous determinants of Ro 60 stratifies autoantibody responses in lupus and primary Sjögren's syndrome.
OBJECTIVE
Analysis of B cell determinants of Ro 60 exposed on the surface of apoptotic cells (apotopes) or intracellular epitopes provides insight into the structural forms of the autoantigen that break immune tolerance. This study was initiated to compare anti-Ro 60 responses in systemic lupus erythematosus (SLE) and primary Sjögren's syndrome (SS) against membrane-bound and intracellular forms of Ro 60.


METHODS
The reactivity of autoantibodies from patients with SLE and primary SS to Ro 60 apotopes and epitopes was assessed by multiparameter flow cytometry and solid-phase immunoassay. Anti-Ro 60 IgG was eluted from early apoptotic cells or recombinant Ro 60 immobilized on nitrocellulose, and binding to membrane-bound and intracellular forms of Ro 60 was quantitated by flow cytometry.


RESULTS
An immunodominant apotope, which was recognized by IgG from a subset of SLE patients with anti-Ro, but not anti-La, autoantibodies, was mapped to a region forming a helix-loop-helix at the apical tip of the Ro 60 molecule. Immobilization of this region to the solid phase exposed an epitope that was recognized by IgG from primary SS and SLE patients whose sera had both anti-Ro and anti-La autoantibodies. Autoantibodies eluted from either the surface of apoptotic cells or the Ro 60 epitope on the solid phase were non-cross-reactive and specifically recognized membrane-bound or cytoplasmic forms of Ro 60.


CONCLUSIONS
This is the first example of a dichotomy of human autoantibody responses against mutually exclusive determinants linked to a single domain of a systemic autoantigen and supports a model in which tolerance is broken by different immunogenic forms of Ro 60.
Flinders Medical Centre, Bedford Park, South Australia, Australia.
Joanne H
JH
Reed
Nadine L
NL
Dudek
Shannon E
SE
Osborne
Kenneth M
KM
Kaufman
Michael W
MW
Jackson
Anthony W
AW
Purcell
Tom P
TP
Gordon
D001323:Autoantibodies / Q000276:immunology*; D001324:Autoantigens / Q000737:chemistry* / Q000276:immunology*; D003429:Cross Reactions / Q000276:immunology; D018604:Epitope Mapping; D005434:Flow Cytometry; D006801:Humans; D016056:Immunodominant Epitopes / Q000737:chemistry / Q000276:immunology; D007074:Immunoglobulin G / Q000276:immunology; D019169:Jurkat Cells; D008180:Lupus Erythematosus, Systemic / Q000276:immunology*; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D020733:RNA, Small Cytoplasmic / Q000737:chemistry* / Q000276:immunology*; D012261:Ribonucleoproteins / Q000737:chemistry* / Q000276:immunology*; D012859:Sjogren's Syndrome / Q000276:immunology*; D000099207:SS-A Antigen
D001323:Autoantibodies; D001324:Autoantigens; D016056:Immunodominant Epitopes; D007074:Immunoglobulin G; D020733:RNA, Small Cytoplasmic; D012261:Ribonucleoproteins; C116006:RO60 protein, human; D000099207:SS-A Antigen