Persistent high levels of IgM antiphospholipid antibodies in a patient with recurrent pregnancy losses and rheumatoid arthritis

Objective: Recurrent pregnancy losses (RPL) and unexplained infertility (UI) are often associated with the presence of antiphospholipid antibodies (APA). We report one case with RPL, UI, and persistent IgM APA without B-cell isotype switch. Method of study: (i) A case report of a woman with RPL and UI who eventually developed rheumatoid arthritis and B-cell phenotype study of the case and controls by flow cytometric analysis; (ii) a retrospective cohort study of 1067 subjects with APA test. Results: A 44-year-old woman with a history of RPL and UI was revealed to have high levels of APA, primarily of IgM isotype: IgM autoantibodies were specific to cardiolipin, phosphatidylglycerol, phosphatidylserine, and phosphatidylinositol. The monitoring of the patient's serological characteristics for 28 months did not reveal the development of IgG APA. B-cell phenotype analysis revealed decreased switched and double negative memory B cells and increased non-switched memory B cells in comparison with normal controls and reported ranges. A retrospective analysis of APA test revealed that total five patients (5/1067, 0.47%) with similar persistent IgM-only pattern were detected. Conclusion: Persistent IgM APA without isotype switch may be a rare variant form of APA manifestation, which is associated with dysregulated B-cell subsets.