Introduction
It is well established that males and females display physiologically relevant, sex-dependent differences (Beery and Zucker, 2011, Lee, 2018, Woitowich et al., 2020, Zucker and Prendergrast, 2020, Plevkova et al., 2021). The immunology field is no exception, as females generally display stronger immune responses than males (Whitacre, 2001, Ngo et al., 2014, Klein and Flanagan, 2016, Qi et al., 2021, Dhakal et al., 2022). These differences between males and females are believed to be at least partially responsible for the stronger incidence of autoimmune diseases in females, and conversely, stronger incidence of cancer and susceptibility to infection in males. As such, having a deeper understanding of the differences between male and female immune systems is key to understanding the pathophysiology of a variety of diseases, and could lead to more fine-tuned therapies (Zucker and Prendergrast, 2020, Pala et al., 2022). In this context, we sought to investigate the implication of sex-bias on the phenotype and function of tissue-resident type-I innate lymphoid cells (ILC1) in two different strains of mice (B6J and BALB/cJ). Like conventional natural killer cells (cNK), ILC1 belong to the group-I innate lymphoid cells family (gILC1), characterized by the lack of genetically rearranged antigen receptors, expression of NK1.1 and/or NKp46, T-bet, a robust production of IFN?, and cytotoxicity. We and others have shown that ILC1 are involved in anti-viral responses to MCMV (murine cytomegalovirus), anti-tumor responses, autoimmunity, and in non-alcoholic liver diseases (NALD) (Weizman et al., 2017, Picarda et al., 2019, Weizman et al., 2019, Cheng et al., 2023a, Evers et al., 2023, Hildreth et al., 2023, Zhang et al., 2023, Marrocco et al., 2025). While studies assessing the role of sex-bias for cNK have been published (Hou and Zheng, 1988, Zientarska et al., 2021, Cheng et al., 2023b), its role in regulating ILC1 remains unclear. ILC1 are resident mainly in non-lymphatic tissues and are well-studied in the liver (Fuchs, 2016, McFarland et al., 2021, Jaeger et al., 2024), but they are also present in the spleen and salivary glands (SG). Here, we compared male and female ILC1 phenotypes in both C57BL/6J (B6J) mice and BALB/cJ mice, focusing mainly on the liver, but also analyzing these other two tissues. We then assessed how sex-bias might impact the ability to control MCMV replication. Our results show that female ILC1 in the liver are more numerous and display higher activation levels (higher expression of CD226, TRAIL, GzmA, GzmB, GzmC) compared to male ILC1, suggesting higher cytotoxic potential. While there was very little sex-bias observed among gILC1 in the spleen, a profound change in the expression of TRAIL, GzmC, Eomes and Ly49H was observed in the salivary glands, all four proteins being drastically decreased in male gILC1 compared with female gILC1. However, these differences did not lead to superior control of MCMV replication in females. As we found that male ILC1 produce more cytokines during MCMV infection, we hypothesize this may counterbalance their lower apparent cytotoxic potential. Alternatively, other cell populations displaying unique phenotypes in males and females could shape ILC1-based differences in vivo. Finally, we analyzed a public dataset of snRNA-seq performed on healthy human livers from both sexes to see if these differences are conserved in humans.
