AUTOANTIBODIES TO A NOVEL EARLY ENDOSOME ANTIGEN-1

Autoantibodies to EEA1, an antigen on early endosomes, were first repo rted in the serum of a patient with subacute cutaneous lupus erythemat osus (SCLE). Here we have examined 38 sera selected for investigation of autoantibodies to EEA1 on the basis of cytoplasmic vesicle-like rea ctivity by immunofluorescence, Ten of the sera were reactive to a HeLa cell protein of approximately the same M-r as human EEA1, Eight of th ese sera belonged to the IgG(1) subclass. Five of the sera reacted wit h fusion proteins incorporating either the amino (from amino acids 1 t o 209) or the carboxyl (incorporating the most C-terminal 300 amino ac ids) terminus of the human EEA1 protein, Antigens reactive with these 5 sera colocalized with internalized transferrin receptors, indicating their association with early endosomes. The other 5 sera which did no t react to both fusion proteins did not colocalize with internalized t ransferrin receptors, We conclude that 5 of the 38 patients (13%) have autoantibodies to EEA1. None of these patients have SCLE, but have ge neralized joint pain, polyarthritis, rheumatoid arthritis, or circulat ing rheumatoid factors. (C) 1998 Academic Press.