B cell metabolic screening in primary antibody-deficiency identifies succination as an inflammatory immuno-metabolic pathology

Cellular metabolic pathway usage and immune cell function are intimately interlinked. Whether screening metabolic activity of defined immune cell subsets has clinical value, or is effective in guiding discovery of molecular immune pathology, has not been previously explored.
Here we prospectively screened glycolysis (extracellular acidification rates – ECAR) and mitochondrial respiration (oxygen consumption rates – OCR) in B cells of healthy subjects (n=15) and patients with primary antibody deficiency (PAD, n = 14). Mean ECAR values were similar in both cohorts, whereas – counterintuitively – mean OCR values were higher in PAD patients. The highest OCR values grouped three study participants with primary polyclonal B cell lymphocytosis (PPBL), a condition characterized by expansion of marginal zone (MZ)-like B cells. Guided by this B cell hyper-respiration phenotype, whole exome sequencing identified rare germline mutations in subunit A of the succinate dehydrogenase (SDHA) gene in these three patients. Functional assays pinpointed SDHA gain-of-function driving fumarate accumulation, which increased succination of several proteins – including KEAP1. Succination of KEAP1 promotes accumulation of the transcription factor Nrf-2, and inhibition of Nrf-2 established that the inflammatory output of MZ-like B cells from PPBL patients was Nrf-2 dependent.
Our study identifies pathologic retrograde signaling as a novel mechanism underlying immune dysregulation in PAD. Specifically, in MZ-like B cells of the PPBL patients enrolled in this study, SDHA-driven accumulation of fumarate engaged retrograde signaling via KEAP1–Nrf-2 to drive transcription of inflammatory cytokines. OCR screening of a clinically justified cell population thus helped to uncover a novel molecular disease mechanisms and pinpointed new therapeutic targets.