The NKCC1 inhibitor bumetanide has no discernible effect on plasma cell survival, persistence or antibody secretion

Long-lived plasma cells (LLPC) sustain humoral immunity but also contribute to the persistence of pathogenic autoantibodies in autoimmune diseases. New therapies targeting LLPC are therefore desirable. Recent studies have shown increased expression of Slc12a2, encoding the Na+ -K+ -Cl- cotransporter (NKCC1), in LLPC. This study investigated whether NKCC1 activity was required for plasma cell survival, persistence or secretion of antibodies. Across in vitro and in vivo settings, mouse plasma cell survival was undiminished by treatment with the NKCC1 inhibitor bumetanide. Acute in vivo bumetanide treatment did not diminish plasma cell numbers, nor show any demonstrable impact on the survival of phenotypically mature I-A/I-EloSLAMF6lo plasma cells. With genetic plasma cell timestamping, even the survival of persistent LLPC was unaffected by bumetanide. Plasma cell secretory capacity, assessed by measuring IgM and IgG2b secretion in culture over three days, was also unaltered by bumetanide. Overall, these results show that pharmacological inhibition of NKCC1 is not sufficient to impair plasma cell survival, persistence or antibody secretion. Despite elevated Slc12a2 mRNA expression in LLPC, NKCC1 alone does not represent a critical plasma cell survival pathway, highlighting the resilience of plasma cells and the challenges associated with therapeutically targeting LLPC.