Abstract
The innate immune system plays a critical early role in host defense against viruses, bacteria, and tumor cells. Until recently, natural killer (NK) cells and lymphoid tissue inducer (LTi) cells were the primary members of the innate lymphocyte family: NK cells form the front-line interface between the external environment and the adaptive immune system, while LTi cells are essential for secondary lymphoid tissue formation. More recently, it has become apparent that the composition of this family is much more diverse than previously appreciated and newly recognized populations play distinct and essential functions in tissue protection. Despite the importance of these cells, the developmental relationships between different innate lymphocyte populations remain unclear. Here we review recent advances in our understanding of the development of different innate immune cell subsets, the transcriptional programs that might be involved in driving fate decisions during development, and their relationship to NK cells.
Highlights
Mucosal surfaces of the body are constantly bombarded with a variety of both innocuous and pathogenic organisms
The group 3 innate lymphoid cell (ILC) (ILC3) produce Th17 type cytokines IL-17 and IL-22. They comprise the classical lymphoid tissue inducer (LTi) cells that are responsible for the generation of lymphoid tissue during embryogenesis, LTi-like cells that are phenotypically similar to LTi cells but are enriched in the intestine of the adult, together with the natural cytotoxicity receptor (NCR)-expressing NKp46+ ILC that produces IL-22 and not IL-17
In contrast to natural killer (NK) cells, we did not observe any expression of Eomes in NKp46+ ILCs or LTi cells indicating that Eomes and T-bet operate in a non-redundant manner in this lineage
Summary
Mucosal surfaces of the body are constantly bombarded with a variety of both innocuous and pathogenic organisms. The group 3 ILCs (ILC3) produce Th17 type cytokines IL-17 and IL-22 They comprise the classical lymphoid tissue inducer (LTi) cells that are responsible for the generation of lymphoid tissue during embryogenesis, LTi-like cells that are phenotypically similar to LTi cells but are enriched in the intestine of the adult, together with the natural cytotoxicity receptor (NCR)-expressing NKp46+ ILC that produces IL-22 and not IL-17. Within these groupings, ILC subsets share some overlapping features in their surface receptor phenotype and cytokine production but are distinct in their requirements for specific different transcription factors. Much has been done in defining the regulatory circuits of B cells (Nutt et al, 2011), T cells (Kaech and Cui, 2012), NK cells (Sun and Lanier, 2011; Bezman et al, 2012), and dendritic cells (DCs; Belz and Nutt, 2012), but the lineage www.frontiersin.org
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