Copyright ©The Author(s) 2017. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Hepatol. Aug 18, 2017; 9(23): 979-989
Published online Aug 18, 2017. doi: 10.4254/wjh.v9.i23.979
Innate lymphoid cells in tissue homeostasis and diseases
Aline Ignacio, Cristiane Naffah Souza Breda, Niels Olsen Saraiva Camara
Aline Ignacio, Cristiane Naffah Souza Breda, Niels Olsen Saraiva Camara, Laboratory of Transplantation Immunobiology, Institute of Biomedical Sciences, Department of Immunology, University of São Paulo, São Paulo, SP 05508-900, Brazil
Author contributions: Breda CNS and Ignacio A contributed equally to this work, generated the figure and table, and wrote the manuscript; Camara NOS designed the aim of the editorial and wrote the manuscript.
Supported by Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), No. 2012/02270-2.
Conflict-of-interest statement: The authors declare that there is no conflict of interest regarding the publication of this paper.
Open-Access: This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See:
Correspondence to: Niels Olsen Saraiva Camara, MD, PhD, Professor, Laboratory of Transplantation Immunobiology, Institute of Biomedical Sciences, Department of Immunology, University of São Paulo, Av. Prof. Lineu Prestes, 1730, Cidade Universitária, São Paulo, SP 05508-900, Brazil.
Telephone: +55-11-30917388 Fax: +55-11-30917224
Received: March 1, 2017
Peer-review started: March 2, 2017
First decision: March 28, 2017
Revised: May 22, 2017
Accepted: June 19, 2017
Article in press: June 20, 2017
Published online: August 18, 2017

Innate lymphoid cells (ILCs) are the most recently discovered family of innate immune cells. They are a part of the innate immune system, but develop from the lymphoid lineage. They lack pattern-recognition receptors and rearranged receptors, and therefore cannot directly mediate antigen specific responses. The progenitors specifically associated with the ILCs lineage have been uncovered, enabling the distinction between ILCs and natural killer cells. Based on the requirement of specific transcription factors and their patterns of cytokine production, ILCs are categorized into three subsets (ILC1, ILC2 and ILC3). First observed in mucosal surfaces, these cell populations interact with hematopoietic and non-hematopoietic cells throughout the body during homeostasis and diseases, promoting immunity, commensal microbiota tolerance, tissue repair and inflammation. Over the last 8 years, ILCs came into the spotlight as an essential cell type able to integrate diverse host immune responses. Recently, it became known that ILC subsets play a key role in immune responses at barrier surfaces, interacting with the microbiota, nutrients and metabolites. Since the liver receives the venous blood directly from the intestinal vein, the intestine and liver are essential to maintain tolerance and can rapidly respond to infections or tissue damage. Therefore, in this review, we discuss recent findings regarding ILC functions in homeostasis and disease, with a focus on the intestine and liver.

Keywords: Innate lymphoid cells, Intestine, Liver, Homeostasis, Inflammatory diseases

Core tip: Receiving approximately 70% of blood through the portal vein, the liver represents one of the most important sites of defense against invading pathogens. In addition, the liver and the intestine are important immune organs, as they are often in contact with antigens and endotoxins produced by the gut microbiota. These organs are densely populated by innate immune cells such as natural killer cells, dendritic cells, macrophages, natural killer T cells and innate lymphoid cells (ILCs), which are rapidly activated by commensal and pathogenic antigens, growth factors, cytokines and host metabolites. Recent studies have been focused on discovering the role of ILCs and how these cell populations can regulate the immune response. Our goal is to discuss innovative literature highlighting the importance of ILCs in the context of infectious disease, tissue repair, tolerance of gut microbiota and inflammatory diseases that affect the liver and intestine homeostasis.