Deciphering the immunoregulatory network governing antigen presenting myeloid cells

SUMMARY Dendritic cells (DC) are responsible for directing T cell responses and macrophages important for modulating tissue inflammation. A hallmark of these immune cells is their inherent plasticity to govern immunity vs. tolerance. However, much remains unknown regarding the complex molecular networks that collectively govern hematopoiesis, inflammation and antigen presentation. Incomplete understanding presents major obstacles to delineating their underlying roles in health and disease, which has also hindered success in developing effective immunotherapies. The long-term goal of the proposed research is to determine how pivotal immunoregulatory proteins govern DC and macrophage differentiation and immune responses. Published findings by my laboratory have begun to mechanistically define the functional roles of several important genes uniquely expressed in these myeloid cells. These genes, which include Allograft Inflammatory Factor-1 (AIF1) and Phosphodiesterase 1b (Pde1b), among others, were identified using a combination of high throughput transcriptomic profiling coupled with rigorous RNAi functional screening. My laboratory demonstrated that AIF1 is selectively expressed in conventional type 1 DC (cDC1), monocyte-derived DC (MoDC) and macrophages and serves as a scaffold to recruit protein kinase C (PKC) in a calcium-responsive manner to promote inflammation and type 1 polarized immune responses. Furthermore, AIF1 expression was required for successful generation of cDC1 from hematopoietic progenitors and both MoDC and macrophages from monocyte precursors. In the context of disease, AIF1 expression in DC and macrophages is required for initiating and sustaining insulitis and in regulating effector responses to intracellular pathogens. In another line of studies, the phosphodiesterase protein Pde1b was found to depress protein kinase A (PKA) activity in a calcium-dependent manner by regulating cyclonucleotide levels in cDC1, MoDC and macrophages to promote immune effector responses. Thus, my research group has begun to unravel how Pde1b works in concert with AIF1 to govern immunity by balancing PKC vs. PKA activities. As important as these initial findings are, there remains several gaps in understanding the molecular mechanics of how these genes govern immunobiology. As such, our research builds on prior studies by now employing conditional and global knockout mice and use of innovative experimental tools to rigorously study mechanistic roles in vivo. My laboratory will pursue the following major goals over the next five years: (1) delineate how AIF1 and Pde1B govern differentiation of DC and macrophages in vivo; (2) describe the intracellular processes by which other key novel immunoregulatory genes orchestrate immune responses; (3) determine the contributing role of AIF1 in initiating inflammation and sustaining autoreactive T cell responses; and (4) identify how intracellular pathogens antagonize AIF1 and Pde1b through disruption of calcium signaling and cyclonucleotide levels to evade host immunity. Knowledge gained will fill key gaps in our understanding of DC and macrophage biology and provide important insights into the molecular networks governing immunity.