CD11c as a novel target to improve neutrophil effector functions and sepsis outcome

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Project Summary/ Abstract Sepsis remains to be associated with a high mortality of 20 to 30% with annual cost of $24 billion, accounting for nearly one-fifth of the total aggregate costs in all the hospitalizations in the United States. Current sepsis management is supportive. Therefore, identifying therapeutic approaches is an urgent task to improve the outcome of sepsis. Neutrophils eradicate microbes as the first-line defense innate immune cells. In sepsis, exaggerated de novo neutrophil production called emergency granulopoiesis occurs mainly via G-CSF production. However, immature neutrophils are also released into a circulation to meet a high demand for neutrophil number, but they have less antimicrobial defense functions, leading to worse host defense in septic patients. G-CSF itself does not trigger full neutrophil maturation. Thus, an intervention to attain the enhancement of neutrophil maturation is critical in sepsis for better host defense. Integrin CD11c was considered a sensitive marker to differentiate sepsis from systemic inflammatory response syndrome. We previously showed that CD11c KO mice had worse survival in the polymicrobial sepsis induced by cecal ligation and puncture (CLP) surgery, indicating the critical role of CD11c in sepsis. There has been a paucity of research about its functional role in vivo. We unexpectedly identified that CD11c was expressed in the bone marrow (BM) neutrophils (largely intracellular) and its deficiency was associated with less BM neutrophil maturation. In a mouse model to recapitulate emergency granulopoiesis, mature neutrophils were released in significantly less quantity in CD11c KO mice compared to wild type (WT) mice, further suggesting its importance in neutrophil maturation. We created CD11c constitutively active knock-in (KI) mice, which demonstrated to have more mature neutrophils in the BM in a steady-state condition and during infection with better bacterial eradication and outcomes. In addition, our in vitro neutrophil maturation experiments using primary murine CD11c KO neutrophils or HL-60 cells devoid of CD11c by CRISPR/Cas9 technology showed less neutrophil maturation. Based on these results, we hypothesized that CD11c activity would significantly regulate the degree of neutrophil maturation in a steady state and emergency granulopoiesis in a cell-intrinsic manner. Our preliminary data suggested that CD11c would also regulate a subset of neutrophil effector functions irrelevant of maturation. Thus, we will determine the role of CD11c in neutrophil maturation and effector functions in a steady state and sepsis in Aim 1 and Aim 2. Because IQGAP1 was suggested to be a binding partner for CD11c, its role will also be studied to delineate the mechanism of how CD11c regulates neutrophil maturation and effector functions. Studies will be done by using human sepsis subjects and murine models. Because there are no CD11c small molecule agonists and antagonists available, we will screen them in Aim 3. Upon the completion of the proposal, we expect that we would solidify that CD11c would be a critical regulator of neutrophil maturation and effector functions for a therapeutic intervention in sepsis.