Introduction: Innate lymphoid cells (ILCs) play a crucial role in immunity by regulating innate and adaptive immune cells and are involved in various physiological processes such as morphogenesis, homeostasis, metabolism, and tissue repair. ILCs are categorized into three primary subgroups: ILC1s, ILC2s, and ILC3s, which are distinguished by their functions and their production of cytokines resembling those of T helper cell subsets. The distribution of ILCs during development, particularly in rats, is not well understood. This study aims to investigate the changes in tissue-specific ILC populations throughout rat development, from embryonic days to postnatal day (PN) 30.Methods: ILC subsets in different organs, such as the liver, lung, spleen, mesenteric lymph nodes (mLN), thymus, small intestine, and colon, were examined through surface and intracellular staining using flow cytometry (FACS Aria III).Results: In the liver, ILC3s were most common before birth, followed by an increase in ILC1s one week after birth, and a rise in ILC2s by the end of the first month after birth. The lung showed an increase in ILC1s and NK progenitor cells after birth, with a decrease in ILC3s by the end of the first month postnatally. The spleen changed from being dominated by ILC3s in the fetal period to being dominated by ILC2s at PN30. In the mLN, ILC2s were the most common subtype throughout development. ILC3s were the main subtype in the thymus, with a decrease in NK cell representation after birth. The small intestine and colon were dominated by ILC2s, with an increase in ILC1s observed in the colon after birth.Conclusions: This study provides insights into the changes in ILC populations during prenatal and postnatal development in rat hematopoietic, lymphoid, and non-lymphoid organs, which can be valuable for researchers studying ILCs and improves the rat model in developmental biology.

Introduction: Innate lymphoid cells (ILCs) play a crucial role in immunity by regulating innate and adaptive immune cells and are involved in various physiological processes such as morphogenesis, homeostasis, metabolism, and tissue repair. ILCs are categorized into three primary subgroups: ILC1s, ILC2s, and ILC3s, which are distinguished by their functions and their production of cytokines resembling those of T helper cell subsets. The distribution of ILCs during development, particularly in rats, is not well understood. This study aims to investigate the changes in tissue-specific ILC populations throughout rat development, from embryonic days to postnatal day (PN) 30.Methods: ILC subsets in different organs, such as the liver, lung, spleen, mesenteric lymph nodes (mLN), thymus, small intestine, and colon, were examined through surface and intracellular staining using flow cytometry (FACS Aria III).Results: In the liver, ILC3s were most common before birth, followed by an increase in ILC1s one week after birth, and a rise in ILC2s by the end of the first month after birth. The lung showed an increase in ILC1s and NK progenitor cells after birth, with a decrease in ILC3s by the end of the first month postnatally. The spleen changed from being dominated by ILC3s in the fetal period to being dominated by ILC2s at PN30. In the mLN, ILC2s were the most common subtype throughout development. ILC3s were the main subtype in the thymus, with a decrease in NK cell representation after birth. The small intestine and colon were dominated by ILC2s, with an increase in ILC1s observed in the colon after birth.Conclusions: This study provides insights into the changes in ILC populations during prenatal and postnatal development in rat hematopoietic, lymphoid, and non-lymphoid organs, which can be valuable for researchers studying ILCs and improves the rat model in developmental biology.