CD28 induces survival in long-lived plasma cells through NFκB mediated Irf4 upregulation and mitochondrial respiration-dependent reactive oxygen species production.

Abstract

Abstract Durable humoral immunity is dependent upon sustained antibody production by long-lived plasma cells (LLPCs). We have published that CD28 is required for LLPC survival and antibody production in vivo; however, the mechanistic basis for this is unclear. In T cells, CD28 is known to induce glycolysis at the expense of respiration. Surprisingly, CD28 induces mitochondrial respiration and biogenesis in LLPCs while also increasing glucose uptake. Paradoxically, respiration-dependent reactive oxygen species (ROS) are required for CD28-mediated survival. Using knock-in mice with mutations in the CD28 cytoplasmic tail, we demonstrate that CD28-Grb2-Vav-Slp76 signaling is required for the survival of LLPCs with high mitochondrial mass and ROS in vivo. Mechanistically, CD28 induces Irf4 in an NFκB-dependent manner. CD28-ROS drive cRel translocation, an NFκB subunit, which can bind directly to the Irf4 promoter. We also describe a super enhancer element further upstream of Irf4 driven by the NFκB subunit p65, induced by CD28 specifically in LLPCs. Furthermore, inhibition of NFκB abrogates CD28-mediated glucose uptake, mitochondrial respiration and biogenesis. Irf4 heterozygous LLPCs have lower mitochondrial mass in vivo, and knock-down of Irf4 decreases the mitochondrial mass. This leads to a model wherein CD28, through Grb2-Vav-Slp-76, reinforces LLPC survival through the induction of mitochondrial biogenesis and respiration. Respiration-dependent ROS then augment NFκB-mediated Irf4 expression through direct promoter activity and a previously undescribed super enhancer element. CD28, therefore, makes an attractive target for the augmentation of vaccine design and in the alleviation of antibody-mediated autoimmunity.