Beyond NK cells: the expanding universe of innate lymphoid cells

Abstract

For a long time, natural killer (NK) cells were thought to be the only innate immune lymphoid population capable of responding to invading pathogens under the influence of changing environmental cues. In the last few years, an increasing amount of evidence has shown that a number of different innate lymphoid cell (ILC) populations found at mucosal sites rapidly respond to locally produced cytokines in order to establish or maintain homeostasis. These ILC populations closely mirror the phenotype of adaptive T helper subsets in their repertoire of secreted soluble factors. Early in the immune response, ILCs are responsible for setting the stage to mount an adaptive T cell response that is appropriate for the incoming insult. Here, we review the diversity of ILC subsets and discuss similarities and differences between ILCs and NK cells in function and key transcriptional factors required for their development.

Keywords: IL-22; NKp44; cytokines; innate lymphoid cells; mucosal tissues.

Figure 1

The major transcriptional pathways that control ILC and NK cell development. Indicated in red are the key transcription factors that have been shown being absolutely required in vivo for the development of each cell subset. “Emergency” NK cells are NK cells that develop in the absence of E4BP4, following viral infection. It is presently unclear whether these cells are Tbet-dependent. CHILP, common helper innate lymphoid precursor; CLP, common lymphoid progenitor; cILC2/ILC3p, common ILC2/ILC3 progenitor.