An early endosome
antigen previously reported by F.T. Mu could be stained on cytoplasmic vesicles of HEp-2 cells. Here, we have investigated
autoantibodies against cytoplasmic vesicular
antigens, especially against
early endosome antigen 1. Twelve sera were selected on the basis of cytoplasmic vesicular staining patterns of HEp-2 cells.
Protein-immunoprecipitation using 35S-methionine labeled HeLa lysates, and
RNA immunoprecipitation using 32P-labeled HeLa lysates were conducted to characterize the cognate
antigens. Nine of 12 sera reacted with
proteins in the range of 162-180 kDa, three of which were found to react specifically with the 162 kDa 35S
methionine labeled recombinant
early endosome antigen 1. These
proteins were not associated with common
RNA. Although complete clinical information was not available, some of the patients had
rheumatoid arthritis(RA). In addition, the
RNA-
IPP results suggest that other patients included one each with SLE, SSc,
polymyositis, and Sjögren's syndrome. Anti-
early endosome antigen 1 antibody was found in 25%(3 of 12) of sera known to
stain cytoplasmic vesicles. The reactive sera came mostly from patients with RA. The sera was from one case each of clinical-confirmed RA, SLE and Sjögren's syndrome.