Therapeutic Potential of B-1a Cells in COVID-19.

Coronavirus disease 2019 (COVID-19) is a life-threatening respiratory illness caused by the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Its clinical presentation can vary from the asymptomatic state to acute respiratory distress syndrome (ARDS) and multi-organ dysfunction. Due to our insufficient understanding of its pathophysiology and lack of effective treatment, the morbidity and mortality of severe COVID-19 patients are high. Patients with COVID-19 develop ARDS fueled by exaggerated neutrophil influx into the lungs and cytokine storm. B-1a cells represent a unique subpopulation of B lymphocytes critical for circulating natural antibodies, innate immunity, and immunoregulation. These cells spontaneously produce natural IgM, interleukin (IL)-10, and granulocyte-monocyte colony stimulating factor (GM-CSF). Natural IgM neutralizes viruses and opsonizes bacteria, IL-10 attenuates the cytokine storm, and GM-CSF induces IgM production by B-1a cells in an autocrine manner. Indeed, B-1a cells have been shown to ameliorate influenza virus infection, sepsis, and pneumonia, all of which are similar to COVID-19. The recent discovery of B-1a cells in humans further reinforces their potentially critical role in the immune response against SARS-CoV-2 and their anticipated translational applications against viral and microbial infections. Given that B-1a cells protect against ARDS via immunoglobulin production and the anti-COVID-19 effects of convalescent plasma treatment, we recommend that studies be conducted to further examine the role of B-1a cells in the pathogenesis of COVID-19 and explore their therapeutic potential to treat COVID-19 patients.