(26) Type 1 Interferon Signaling Influences Monocyte/macrophage h3k4me3 and Antiviral Function Throughout the Lifespan

Background: The neonatal immune response is distinct from that of adults, with defects in both the innate and adaptive immune systems. Monocytes and macrophages are central to innate immune responses and demonstrate a developmental stage-specific gain in H3K4me3, a mark generally associated with active transcription, at immunologically important gene promoters. This developmental gain is associated with more functional pathogen responses as development progresses from neonate to adult, but the factors underlying this are unclear. Type 1 interferon signaling, induced by the intestinal microbiota, is critical for appropriate immune homeostasis and function. IFN-I signaling also guides innate immune cell H3K4me3 deposition, but this has not been studied in neonatal cells.

Objectives: Perturbations in type 1 interferon signaling using mice that lack IFN-I signaling (IFNAR-/-) will decrease H3K4me3 deposition or conversely, mice with constitutive low-grade IFN-I expression (IRGM1-/-) will display increased H3K4me3 in monocytes/macrophages. Together these stage specific differences in H3K4me3 will alter in vitro and in vivo cell function and phenotype.

Design/Methods: Monocytes/macrophages were isolated from neonate (P4-5), infant (P12-16), and adult (8 weeks), wild-type (WT), IFNAR-/-, or IRGM1-/- mice using a CD11b+ selection kit. Isolated monocytes were assessed for 1) H3K4me3 patterns using Chromatin Immunoprecipitation (ChIP)-Sequencing and 2) stimulated in vitro with Influenza A and respiratory syncytial virus (RSV) to assess cytokine levels by multiplex protein assay and mRNA by qPCR. Neonatal mice (0.5LD50), infant mice (2.5LD50) and adult mice (LD50) were infected with Influenza A (PR8) and monitored for mortality and the airway function by PenH.

Results: Chronic low-grade IFN-I signaling (IRGM1-/-) in neonatal mice increased H3K4me3 marks compared to WT neonatal mice. Pathway analysis identified antiviral response pathways to contain significantly more H3K4me3 in IRGM1-/- and significantly less H3K4me3 in IFNAR-/- mice at all developmental stages. These include the antiviral genes OAS1A, OAS2, OAS3 and IFI27l2. These differences were associated with improved in vitro antiviral responses and improved in vivo survival in neonatal IRGM1-/- mice following Influenza A infection without differences noted in more developmentally mature mice.

Conclusions: Together, these data highlight the importance of appropriate IFN-I signaling in immune cell development and function, particularly during the neonatal period.