Restricted epitope recognition by precipitin-negative anti-La/SS-B-positive sera.
OBJECTIVE
To determine whether anti-La/SS-B-positive sera that are precipitin negative show a distinct B cell epitope pattern.


METHODS
Serum reactivity was tested with recombinant La/SS-B fusion proteins.


RESULTS
Among the 18 precipitin-negative anti-La/SS-B-positive sera, reactivity was confined to the full-length recombinant protein (La33.3) in 8 (44%); 5 of 18 (28%) reacted only with La33.3 and with the first 107 N-terminal amino acids (LaA), and 4 (22%) reacted with La33.3, LaA, and the middle region of the La molecule (LaC; amino acids 111-242). One serum reacted with La33.3 and LaC. None of the 18 precipitin-negative sera was positive on a carboxy-terminal fragment (LaL2/3; amino acids 346-408). In contrast, all 26 precipitin-positive anti-La/SS-B-positive sera reacted with La33.3, LaA, and LaC, and 92% reacted with LaL2/3. Rheumatoid factor and serum IgG levels were significantly lower in the precipitin-negative group, providing further evidence of a distinct serologic subset.


CONCLUSIONS
The restricted epitope recognition by these sera may explain the lack of precipitin formation and may represent an early autoantibody response to La/SS-B.
Gordon
T
T
Department of Clinical Immunology, Flinders Medical Centre, Bedford Park, South Australia.
Mavrangelos
C
C
McCluskey
J
J
D001323:Autoantibodies / Q000097:blood*; D001324:Autoantigens / Q000276:immunology*; D001402:B-Lymphocytes / Q000276:immunology; D004797:Enzyme-Linked Immunosorbent Assay; D000939:Epitopes; D006801:Humans; D007074:Immunoglobulin G / Q000032:analysis; D011233:Precipitin Tests; D012217:Rheumatoid Factor / Q000032:analysis; D012261:Ribonucleoproteins; D000097585:SS-B Antigen
D001323:Autoantibodies; D001324:Autoantigens; D000939:Epitopes; D007074:Immunoglobulin G; D012217:Rheumatoid Factor; D012261:Ribonucleoproteins; D000097585:SS-B Antigen