Subtype-specific functions of basal IFNλs
Type III interferons (IFNλs) represent the newest interferon family, comprising four human subtypes (IFNλ1–4) that signal through the tissue-restricted IFNLR1 receptor. While traditionally characterized as antiviral cytokines protecting mucosal barriers, accumulating evidence suggests that IFNλs possess broader physiological roles that remain incompletely understood. A critical gap in our knowledge concerns whether the four IFNλ subtypes function redundantly, or serve distinct biological purposes. Understanding subtype-specific IFNλ functions has become increasingly urgent as these cytokines enter clinical development. Critical questions remain. Addressing these questions will illuminate fundamental principles of mucosal immunity and guide rational design of IFNλ-based therapeutics that maximize protection while preserving epithelial health.