Early-life Fungal Colonization Reveals Stage-specific Immune Regulation in the Oral Mucosa 2241171

Introduction Neonates possess a developing immune system, which is different from adults as a result of initially living in a semi-allogeneic sterile environment to then being exposed to a microbial-rich surrounding, rendering newborns highly susceptible to infections. Following microbial exposure, the mucosal immune system of neonates goes through successive, non-redundant phases that support the developmental needs of the infant to establish immune homeostasis. However, it remains unknown how neonates prevent fungal outgrowth during colonization, representing a critical gap in knowledge. Methods To address this, we developed a novel mouse model of neonatal commensal Candida albicans colonization that results in persistent fungal presence. Single cell RNA sequencing was utilized to obtain a comprehensive view of gene expression dynamics. Results Early during colonization, proinflammatory cytokines were downregulated with increased porpotion of CD25+ Foxp3+ Treg and CD25+ Foxp3- T cells, likely to mitigate excessive immune activation and promote tolerance. Unexpectedly, CCL11 levels were elevated during early fungal persistence. Neutralization of CCL11 reduced oral fungal burden, suggesting a role in mediating tolerance. Later during colonization, IL-22-mediated immunity and associated tissue remodeling plays a critical role in controlling fungal burden and preventing fungal invasion. Furthermore, single-cell RNA sequencing revealed dynamic shifts in immune cell subpopulations over time. Conclusion In summary, neonatal fungal colonization elicits dynamic immune responses that contribute to maintaining homeostasis at the oral mucosal barrier.