Given the success of Volume I of this Research Topic, and the rapidly evolving subject area, we are pleased to announce the launch of Volume II: The Function of Phagocytes in Non-Mammals.

Non-mammalian animals are useful models for understanding the evolution of the immune system and studying the underlying mechanisms of cellular and molecular responses in mammalian immunity. In 1882, Elie Metchnikoff discovered cells surrounding a wound in starfish larvae and named them “phagocytes” based on his hypothesis that these cells surround and kill pathogens. Recent literature has expanded the function of phagocytes beyond pathogen killing to the regulation of the overall inflammation response. In humans, many diseases, including congenital neutropenia, familial Mediterranean fever, and sepsis, stem from dysregulated phagocyte function, with no satisfactory treatment regimens currently available. Because of the high degree of conservation present in basic functions of the innate immune system, it is our opinion that research on non-mammalian phagocytes will provide novel insight into new paradigms for mammalian phagocyte counterparts. For example, extracellular chromatin from phagocytes participates in host defenses found in both invertebrates and vertebrates. Indeed, the use of zebrafish models have advanced our understanding of phagocyte functions, in human tuberculosis, for example.

The regulation of phagocytes in non-mammals is also diverse. Phagocytes in mammals consist mainly of macrophages and neutrophils, while in teleosts B lymphocytes and thrombocytes from peripheral blood also have potent phagocytic activity. Teleost-specific genome duplication events produce genes with overlapping functions, potentially resulting in sub-functionalization in the teleost immune system. An example of this is CXCR3.1 and CXCR3.2 in teleosts, which differentially contribute to macrophage polarization. In invertebrates, such as drosophila, mosquito, cuttlefish, and shrimp, hemocytes display phagocytic activities. Recently, two main mosquito hemocytes have been identified at single-cell resolution and proliferating granulocyte populations are observed.

In this Research Topic, we aim to clarify and review the regulation of phagocytes in non-mammals. Investigating the regulation of phagocytes in non-mammalian systems provides a unique opportunity to improve our understanding of the mechanisms that help regulate immunity generally, and in turn, improve our treatment of infectious diseases in both animals and humans. We welcome the submission of Original Research and Review articles that include, but are not limited to, the following topics:

1. Phagocyte development, differentiation, migration, and apoptosis

2. Anti-microorganism functions of phagocytes

3. Phagocytes in tissue development, homeostasis, and repair

4. Phagocyte activation and polarization

5. Phagocyte role in disease processes

6. Orchestration of metabolism in phagocytes

7. Evolutionary and comparative perspectives of phagocytes

8. Phagocyte regulation by soluble proteins such as cytokines

9. Receptor activation and regulation of phagocytes

10. Intracellular signaling pathways of phagocytes

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Frontiers in Immunology

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