Coupled analysis of transcriptome and BCR mutations reveals role of OXPHOS in affinity maturation.

Antigen-activated B cells diversify variable regions of B cell antigen receptors by somatic hypermutation in germinal centers (GCs). The positive selection of GC B cells that acquire high-affinity mutations enables antibody affinity maturation. In spite of considerable progress, the genomic states underlying this process remain to be elucidated. Single-cell RNA sequencing and topic modeling revealed increased expression of the oxidative phosphorylation (OXPHOS) module in GC B cells undergoing mitoses. Coupled analysis of somatic hypermutation in immunoglobulin heavy chain (Igh) variable gene regions showed that GC B cells acquiring higher-affinity mutations had further elevated expression of OXPHOS genes. Deletion of mitochondrial Cox10 in GC B cells resulted in reduced cell division and impaired positive selection. Correspondingly, augmentation of OXPHOS activity with oltipraz promoted affinity maturation. We propose that elevated OXPHOS activity promotes B cell clonal expansion and also positive selection by tuning cell division times.

Viperin interacts with PEX19 to mediate peroxisomal augmentation of the innate antiviral response.

Peroxisomes are recognized as significant platforms for the activation of antiviral innate immunity where stimulation of the key adapter molecule mitochondrial antiviral signaling protein (MAVS) within the RIG-I like receptor (RLR) pathway culminates in the up-regulation of hundreds of ISGs, some of which drive augmentation of multiple innate sensing pathways. However, whether ISGs can augment peroxisome-driven RLR signaling is currently unknown. Using a proteomics-based screening approach, we identified Pex19 as a binding partner of the ISG viperin. Viperin colocalized with numerous peroxisomal proteins and its interaction with Pex19 was in close association with lipid droplets, another emerging innate signaling platform. Augmentation of the RLR pathway by viperin was lost when Pex19 expression was reduced. Expression of organelle-specific MAVS demonstrated that viperin requires both mitochondria and peroxisome MAVS for optimal induction of IFN-ß. These results suggest that viperin is required to enhance the antiviral cellular response with a possible role to position the peroxisome at the mitochondrial/MAM MAVS signaling synapse, furthering our understanding of the importance of multiple organelles driving the innate immune response against viral infection.