Affinity war: forging immunoglobulin repertoires.

B cell immunoglobulin (Ig) repertoire composition shapes immune responses. The generation of Ig diversity begins with Ig variable region exon assembly from gene segments, random inter-segment junction sequence diversity, and combinations of Ig heavy and light chain. This generates vast preemptive sequence freedom in early developing B lineage cell Ig genes that can anticipate a great diversity of threats. This freedom is met with large restrictions that ultimately define the naïve (i.e. preimmune) Ig repertoire. Activation-induced somatic hypermutation (SHM), which further diversifies Ig V regions, is also met with strong selection that shapes Ig affinity maturation. While individual repertoire features, such as affinity for self and competition for foreign antigen, are known to drive selection, the selection filters themselves may be subject to regulation. Large sequence freedom coupled with strong selection for each diversification process provides flexibility for demand-driven regulation to dynamically balance antigen recognition capacities and associated autoimmune risks according to host needs.