Follicular dendritic cells restrict IL4 availability in germinal centers and foster memory B cell generation

Germinal centers (GCs) are sites of antibody affinity maturation and memory B cell generation. Follicular dendritic cells (FDCs) form a dense stromal network within GCs, but the full extent of their supportive activity is not understood. Here we showed that FDCs expressed IL4Ra and they reduced IL4 availability in GCs. We used scRNA-seq to examine IL4 actions within the GC and identified a subset of light zone cells marked by high IL4Ra and CD23 and lack of a Myc gene-expression signature. Trajectory inference analysis suggested this population could differentiate into pre-memory and pre-plasma cells. Genetic experiments showed that IL4Ra and STAT6 acted intrinsically to restrain pre-memory B cell generation. By reducing IL4 availability, FDCs enhanced GC B cell selection and fostered memory cell generation. This work suggests that GC FDCs provide a niche that limits bystander IL4 activity, focusing IL4 action on B cells undergoing selection and enhancing memory cell differentiation Overall design: Adult mice were immunized intraperitoneally with NP-haptenated antigen in alum adjuvant. GC B cell were sorted at different days after immunization for scRNA-seq.