ILC1

ILC1 stands for innate lymphoid cell type 1, a subset of innate lymphoid cells that produce interferon-gamma (IFN-γ) in response to cytokine signals, in the absence of antigen receptors. ILC1s are lineage-negative lymphocytes enriched in tissues such as the gut and liver, where they participate in early defense against intracellular pathogens and help shape subsequent adaptive responses. They share functional features with Th1 cells but lack the antigen-specific receptors of T or NK cells.

Development and lineage: ILC1s arise from common lymphoid progenitors and develop under the influence of transcription factors including T-bet. They are considered distinct from natural killer (NK) cells, which rely on Eomesodermin and possess cytotoxic functions; ILC1s are typically less cytotoxic and rely more on T-bet-driven cytokine production.

Phenotype and markers: ILC1s are generally Lin- (lineage negative) and express the IL-7 receptor alpha chain (CD127). Marker expression varies by tissue, and ILC1s can express NK cell–related receptors such as NKp46 in some contexts, but they do not display the same cytotoxic program as NK cells.

Function and relevance: In response to signals such as IL-12 and IL-18, ILC1s produce IFN-γ and TNF-α, promoting macrophage activation and control of intracellular pathogens. They contribute to tissue homeostasis and inflammation and can influence downstream adaptive responses. Dysregulation of ILC1 activity has been linked to inflammatory diseases and altered anti-microbial immunity.

Research continues to delineate their development, tissue distribution, and interaction with other ILC subsets.