Lymphoid tissue inducer—A divergent member of the ILC family

Feb 19, 2018Cytokine & growth factor reviews

Lymphoid Tissue Inducer, a Unique Member of the Innate Lymphoid Cell Family

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Abstract

Innate lymphoid cells (ILCs) include a unique subset known as lymphoid tissue inducer (LTi) cells, which are critical for lymphoid organ development.

LTi cells are primarily developed during the fetal stage and have a distinct progenitor compared to other ILCs and conventional natural killer cells.
These cells express the transcription factor RORγt and can produce the cytokine IL-22, contributing to immune responses against extracellular bacteria.
LTi/LTi-like cells exhibit unique gene expression patterns and specialized functions that influence T and B cell development and activation.
The review suggests that LTi/LTi-like cells should be recognized as a separate lineage within the innate lymphoid cell family.

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Innate lymphoid cells (ILCs) that are capable of producing effector cytokines reminiscent of CD4T helper (Th) cells during infections and tissue inflammations have drawn much attention in the immunology field in recent years. Within the ILCs, the lymphoid tissue inducer (LTi) cells that play a critical role in lymphoid organogenesis were identified long before the establishment of the ILC concept. LTi cells, developed and functioning mainly at the fetal stage, and LTi-like cells, presumably generated during the adulthood, are regarded as a subset of type 3 ILCs (ILC3s) because they express the ILC3 lineage-defining transcription factor RORγt, and like other ILC3s, can produce an ILC3 signature cytokine IL-22 and initiate protective immune responses against extracellular bacteria. However, LTi/LTi-like cells have a unique gene expression pattern, and they develop from a progenitor that is distinct from the progenitor of all other ILCs and the progenitor of conventional natural killer (cNK) cells. There are also several other unique features of LTi/LTi-like cells comparing to non-LTi ILC3s. In addition to their classical function in lymphoid organogenesis, LTi/LTi-like cells also have specialized functions in association with the adaptive immune system, which include their effects on T and B cell development, activation and function. In this review, we summarize these specific features of LTi/LTi-like cells and propose that these cells should be considered as a separated innate lymphoid lineage in parallel with other non-LTi ILCs and cNK cells. +

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