Anti‐early endosome antigen 1 autoantibodies were detected in a pemphigus‐like patient but not in the majority of pemphigus diseases

<jats:title>Abstract</jats:title><jats:p>Although the major autoantigens in classic pemphigus are desmogleins, sera from various types of pemphigus react with a number of other molecules, including desmocollins and plakin proteins. However, other novel pemphigus‐related autoantigens remain to be identified. In this study, <jats:bold>i</jats:bold>mmunoblotting for serum from an atypical autoimmune bullous disease patient identified an unknown 175 <jats:styled-content style="fixed-case">kD</jats:styled-content>a protein. Subsequent studies using two‐dimensional gel electrophoresis, immunoblotting and mass‐spectrometry identified the 175 kDa protein as early endosome antigen 1 (<jats:styled-content style="fixed-case">EEA</jats:styled-content>1). This finding was confirmed by subsequent immunological studies, including indirect immunofluorescence of skin and cultured keratinocytes, two‐dimensional gel electrophoresis and immunoblotting with anti‐<jats:styled-content style="fixed-case">EEA</jats:styled-content>1 polyclonal antibody, and preabsorption with <jats:styled-content style="fixed-case">EEA</jats:styled-content>1 recombinant protein. Finally, we developed a novel <jats:styled-content style="fixed-case">BIOCHIP</jats:styled-content> assay using full‐length <jats:styled-content style="fixed-case">EEA</jats:styled-content>1 recombinant protein to detect anti‐<jats:styled-content style="fixed-case">EEA</jats:styled-content>1 antibodies. However, none of 35 sera from various types of pemphigus showed anti‐<jats:styled-content style="fixed-case">EEA</jats:styled-content>1 antibodies in the <jats:styled-content style="fixed-case">BIOCHIP</jats:styled-content> assay, with the exception of the serum from the index case. In addition, various findings in the index case did not suggest pathogenic role of anti‐<jats:styled-content style="fixed-case">EEA</jats:styled-content>1 autoantibodies. Therefore, although we successfully identified the 175 <jats:styled-content style="fixed-case">kD</jats:styled-content>a protein reacted by a serum of an atypical pemphigus‐like patient as <jats:styled-content style="fixed-case">EEA</jats:styled-content>1, novel <jats:styled-content style="fixed-case">BIOCHIP</jats:styled-content> study for other pemphigus sera indicated that <jats:styled-content style="fixed-case">EEA</jats:styled-content>1 is not a common and pathogenic autoantigen in pemphigus.</jats:p>