Background Neither the underlying pathogenesis of alopecia areata (AA) nor the molecular mechanisms leading to hair loss have been fully elucidated. Objectives To compare the protein profiles of sera obtained from patients with AA with those from healthy controls. Methods Protein profiles of sera obtained from subjects with AA and healthy controls were compared using proteomics techniques. Serum levels of the identified protein were quantified by specific enzyme-linked immunosorbent assay (ELISA). The relative serum reactivities of the recombinant human protein were compared between patients with AA and healthy controls using Western blots and double indirect immunofluorescence. Results The upregulated expression of retinol-binding protein (RBP) 4 was identified, and RBP4 ELISA demonstrated significantly increased serum levels of RBP4 among subjects with AA when compared with healthy controls. Western blots using recombinant human RBP4 and the sera from both groups presented serum reactivity of antihuman recombinant RBP4 IgG antibodies in 10/15 subjects with AA (67%) and 2/15 healthy controls (13%). Double indirect immunofluorescence demonstrated merged fluorescence signals of serum anti-RBP4 IgG antibodies and monoclonal antibodies to RBP4 in subjects with AA on the outer root sheath and companion layer. Conclusions Our data demonstrate that AA is associated with increased serum levels of RBP4 and positive IgG immunoreactivity against recombinant human RBP4. These results suggest that the major components for the retinoic acid biosynthesis pathway may be crucially involved in the pathogenic process of AA.
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