Using neutrophils as a tool for trained immunity in macrophages

About This Grant

Macrophages (MFs) play many critical roles in tissue health and disease pathologies. Tissue-resident MFs maintain tissue homeostasis and fulfill key functions, while monocyte-derived MFs infiltrate the tissue upon challenge and drive the inflammatory responses. Autoimmune diseases, such as Rheumatoid Arthritis (RA), are characterized by recurring inflammatory flares driven by MFs with an impaired transition to resolution and wound healing that leads to exacerbated tissue damage and worsened disease outcomes. Such damaging inflammation may be modulated by trained immunity, whereby prior stimulation of MFs leads to a functional memory that drives response to future immune challenges. Thus, approaches to train MF functional memory by limiting their inflammatory response and elevating their pro-repair functions is critical to the development of therapeutic strategies to maintain remission states by preventing disease flares. Our overarching goal is to investigate neutrophil (PMN) priming as a method of MF functional training. Emerging evidence demonstrates that PMNs in acute inflammation can instruct MF activity as a part of normal immune response. This includes the well- established MF reprogramming during the efferocytosis process in the disease resolution phase, as well as via less understood contact or soluble factors dependent interactions. However, whether such training also leads to innate immune MF memory is unknown. Our preliminary data demonstrate frequent dynamic interactions of live PMNs with tissue resident/infiltrating MFs in inflamed tissue in several inflammation models, indicative of an active crosstalk and potential cross cell instruction. Furthermore, studying PMN-MF interactions through transwells revealed that ex vivo pro- vs anti-inflammatory PMN stimulation/priming differentially impacted MF transcriptional regulation without phagocytosis. Thus, we hypothesize that primed PMNs can trigger MF trained immunity, promoting their pro-repair activity in inflamed joint. We will test this hypothesis by determining whether PMNs can train MF functional memory guiding long-term responses to inflammatory stimuli and whether this can help resolve inflammation in vivo. In Aim1, we will establish the impact of differentially primed PMNs on MF functional memory using transwell co-cultures to assess the impact of pro- vs anti- inflammatory priming of PMN on MF responses and their functional memory upon inflammatory rechallenge. In Aim 2, we will determine if PMNs instruction of MFs can be used to attenuate and/or resolve inflammation in STIA (serum-transfer-induced arthritis), a mouse model of RA, by adoptively transferring primed PMNs into mouse joints prior to disease onset. While memory is a well-studied feature of adoptive immunity, its potential for innate immune cells has not been fully explored. Thus, through these conceptually and technically innovative experiments, we expect to establish the possibility of long-term innate immune instructional crosstalk resulting in functional memory and identify novel regulatory mechanisms of trained immunity in MFs with important implications for designing future treatments of inflammatory disorders.