Germinal center structure and function: lessons from CD19.

The germinal center is a critical locus in the production of protective immunity, but its function is poorly understood. Studies of mutant forms of CD19 revealed differences in signaling in different compartments inside the germinal center, and structural findings indicate a selective role in the interaction with follicular dendritic cells in the GC. Loss of these signals leads to surprising changes in germinal center B cells that challenge previous models of GC function.