Molecular mimicry is the most common mechanism that breaches self-tolerance. We previously identified autoantibodies to aquaporin-5 (AQP5) in the sera of patients with Sjögren’s syndrome and found that the aquaporin of Prevotella melaninogenica (PmAqp), an oral commensal, is highly homologous to human AQP5. This study aimed to test whether PmAqp can induce anti-AQP5 autoantibodies via molecular mimicry. From the amino acid sequence of PmAqp, an immunizing peptide; i.e., PmE-L, was designed, which contained both the B cell epitope “E” and T cell epitope. C57BL/6 and BALB/c mice were subcutaneously immunized with linear or cyclic forms of PmE-L emulsified in incomplete Freund’s adjuvant. The concentrations of the antibodies in sera were measured using enzymelinked immunosorbent assays. Both linear and cyclic PmE-L induced high levels of antibodies against not only the immunized peptides but also autoantibodies against AQP5E and antibodies against PmE, a Pm homolog of AQP5E. In C57BL/6 mice; however, the cyclic form of PmE-L was more efficient than the linear form in inducing autoantibodies against AQP5E that contained a cyclic epitope. The levels of anti-PmE antibodies and anti-AQP5E autoantibodies showed a strong positive correlation (r = 0.95, p < 0.0005), suggesting molecular mimicry. Collectively, the mice produced anti-AQP5E autoantibodies in response to a PmAqp-derived peptide. This model proved to be useful for studying the mechanisms of autoantibody production by molecular mimicry.

Prognosis of the patients with lung cancer with lung-to-lung metastasis are known to be poor and frequently old aged persons with multiple nodules on imaging study abandon more invasive procedure including bronchoscopy and VATS (Videoassisted thoracoscopic surgery) to get tissue confirmation. Sjogren’s syndrome (SS) associated lung lesion mimicking lung cancer has a chance to have more favorable diseases including lymphoma. A 78-year-old woman with SS was admitted due to slowly progressive exertional dyspnea and multiple nodules on imaging study. She and her family gave up invasive diagnostic procedures at first due to old age but short term rapid change of dyspnea and nodules on chest CT brought out invasive procedures and diffuse large B-cell lymphoma was diagnosed. Dyspnea and nodules on imaging were improved after R-CHOP chemotherapy.

Primary progressive aphasia (PPA) is a progressive degenerative disorder that primarily affects language. Although the etiology of PPA has not been determined, autoimmune mechanism is known to be one possible pathophysiology. We investigate efficacy of steroid treatment in a patient diagnosed as both logopenic variant PPA and Sjögren's syndrome. After steroid treatment, her cognitive function, especially language ability showed improvement. And also, FDG-PET showed metabolic increase in the bilateral temporal lobe. However, on reassessment after stopping steroid treatment, her cognitive performance declined to pretreatment level.