IL-7 receptor and VDJ recombination: Trophic versus mechanistic actions

Interleukin-7 (IL-7) is required for normal lymphoid development. The rearrangement of receptor genes is induced in lymphoid progenitors during their period of IL-7 dependency. The question addressed in this review is: to what extent does IL-7 control the gene rearrangement process? There are two principal types of controls considered. The first is the 'trophic' effect: IL-7 maintains the viability of cells during gene rearrangement, whereas the signal to induce gene rearrangements may be distinct from IL-7. The second possible control is 'mechanistic': IL-7 delivers signals to induce gene rearrangement as well as maintains cell viability. This review covers current thought on how gene rearrangement is regulated and evaluates recent evidence for a mechanistic action of the IL-7 receptor in gene rearrangement.