Group 3 innate lymphoid cells (ILC3s) are innate immune effectors that contribute to host defense. Whether ILC3 functions are stably modified after pathogen encounter is unknown. Here, we assess the impact of a time-restricted enterobacterial challenge to long-term ILC3 activation in mice. We found that intestinal ILC3s persist for months in an activated state after exposure to Citrobacter rodentium . Upon rechallenge, these “trained” ILC3s proliferate, display enhanced interleukin-22 (IL-22) responses, and have a superior capacity to control infection compared with naïve ILC3s. Metabolic changes occur in C. rodentium –exposed ILC3s, but only trained ILC3s have an enhanced proliferative capacity that contributes to increased IL-22 production. Accordingly, a limited encounter with a pathogen can promote durable phenotypic and functional changes in intestinal ILC3s that contribute to long-term mucosal defense.

An orchestrated cellular network, including adaptive lymphocytes and group 3 innate lymphoid cells (ILC3s), maintains intestinal barrier integrity and homeostasis. T cells can monitor environmental insults through constitutive circulation, scanning tissues and forming immunological contacts, a process named immunosurveillance. In contrast, the dynamics of intestinal ILC3s are unknown. Using intravital imaging, we observed that villus ILC3s were largely immotile at steady state but acquired migratory ‘patrolling’ attributes and enhanced cytokine expression in response to inflammation. We showed that T cells, the chemokine CCL25 and bacterial ligands regulated intestinal ILC3 behavior and that loss of patrolling behavior by interleukin-22 (IL-22)-producing ILC3s altered the intestinal barrier through increased epithelial cell death. Collectively, we identified notable differences between the behavior of ILC3s and T cells, with a prominent adaptation of intestinal ILC3s toward mucosal immunosurveillance after inflammation.

Group 3 innate lymphoid cells (ILC3) actively participate in mucosal defense and homeostasis through prompt secretion of IL-17A, IL-22, and IFN-γ. Reports identify two ILC3 lineages: a CCR6⁺T-bet⁻ subset that appears early in embryonic development and promotes lymphoid organogenesis and a CCR6⁻T-bet⁺ subset that emerges after microbial colonization and harbors NKp46⁺ ILC3. We demonstrate that NKp46 expression in the ILC3 subset is highly unstable. Cell fate mapping using Ncr1^CreGFP × Rosa26^RFP mice revealed the existence of an intestinal RFP⁺ ILC3 subset (Ncr1^FM) lacking NKp46 expression at the transcript and protein levels. Ncr1^FM ILC3 produced more IL-22 and were distinguishable from NKp46⁺ ILC3 by differential CD117, CD49a, DNAX accessory molecule-1, and, surprisingly, CCR6 expression. Ncr1^FM ILC3 emerged after birth and persisted in adult mice following broad-spectrum antibiotic treatment. These results identify an unexpected phenotypic instability within NKp46⁺ ILC3 that suggests a major role for environmental signals in tuning ILC3 functional plasticity.

Group 3 innate lymphoid cells (ILC3) are innate effector cells that have essential roles in lymphoid organogenesis and maintenance of tissue homeostasis under steady-state and pathogenic conditions. ILC3 also promote immune defense, notably during bacterial breach of epithelial barriers, including those caused by attaching and effacing (A/E) pathogens for which Citrobacter rodentium infection in mice is a relevant pre-clinical model. Through their ability to sustain interactions with tissue-resident immune cells, epithelial cells, neurons or stromal cells, ILC3 constitute a key orchestrator that maintains the intestinal barrier. In this review, we will examine the function of murine ILC3 in host defense against C. rodentium infection and provide a discussion of recent advances that help elucidate the specific roles of these novel innate immune effector cells at mucosal surfaces.

Lymph nodes (LNs) can act as reservoirs in CD20 ⁺ B cell malignancies and autoimmune diseases. Although anti-CD20 monoclonal antibodies (mAbs) have substantially improved patient outcomes, relapse and disease progression remain frequent, underscoring critical limitations that constrain their full therapeutic potential. Here, we reveal that the LN microenvironment is an important modulator of anti-CD20 mAb efficacy. Within LNs, malignant B cells can exhibit a sessile, tissue-retained behavior, which limits their access to the blood circulation required for efficient systemic antibody-mediated cell depletion. Although LN B cells are spatially segregated from FcγR ⁺ effector cells, remodeling of the LN microenvironment through irradiation enabled anti-CD20 mAb-mediated B cell depletion. Our findings identify LN architecture as a structural barrier to depleting antibody-based therapies and highlight tissue remodeling as a strategy to enhance therapeutic responses within lymphoid organs.