Distinct Neutrophil Populations in the Spleen During PICS

Abstract

While mortality after acute sepsis has decreased, the long-term recovery for survivors is still poor, particularly those developing persistent inflammation, immunosuppression, and catabolism syndrome (PICS). While previously thought that activated neutrophils responding to the acute phase of sepsis migrate to the spleen to undergo cell death and contribute to immunosuppression, our data show a significant accumulation of distinct, yet functional, neutrophil populations in the spleen in a murine model of PICS. The exact role and function of neutrophils in this response is still unclear. The objective of our study was to better define the immune function of splenic neutrophils to determine if this could give insight into the pathogenesis of PICS. Using a murine model of cecal ligation and puncture (CLP), which demonstrates all characteristics of PICS by 8 days, spleens were harvested, and neutrophils were identified by Ly6G and CD11b expression via flow cytometry. Nearly all splenic neutrophils expressed CD54, but there were distinct CD54 hi and CD54 lo cells, with the majority being CD54 lo cells during PICS. The CD54 hi population showed traditional, proinflammatory properties, but a relatively decreased chemotactic response, while CD54 lo cells had significantly higher chemotaxis, yet significantly decreased proinflammatory functions. Using 5-ethynyl-2 ′-deoxyuridine (EdU) incorporation, we found that the CD54 hi population on day 2 after CLP may be participating in emergency myelopoiesis. However, the vast majority of the CD54 lo population were paused in the G 1 phase at this time point and not proliferating. By day 8 after CLP, most of the CD54 hi cells in the spleen were no longer proliferating, while the CD54 lo cells were, indicating that CD54 lo dominate in extramedullary myelopoiesis at later time points. Almost none of the neutrophils produced arginase or inducible nitric oxide synthase (iNOS), indicating that these are not suppressor cells. Overall, our data demonstrate that neutrophil accumulation in the spleen during PICS is related to extramedullary myelopoiesis, leading to the production of immature neutrophils. While not suppressor cells, the majority have greater chemotactic function but less inflammatory responsiveness, which may contribute to the immunosuppression seen in PICS. Attention to these distinct neutrophil populations after septic or other systemic inflammatory responses is therefore critical to understanding the mechanisms of PICS.

TPPU treatment of burned mice dampens inflammation and generation of bioactive DHET which impairs neutrophil function

“…As described above, we assessed the contribution of neutrophil subtypes to ROS production. We confirm previous results 23 by showing that the mature CD62L-/ICAM-1 + and CD62L + /ICAM-1 + phenotypes contribute the most to ROS production (Fig. 3 A).…”

“…In previous studies, we and others depicted that the CD62L-/ICAM-1 + phenotype can be considered mature and shows increased functionality compared to other phenotypes (Fig. 3 A) 18 , 23 . Therefore, we interpret the observed effect of neutrophils being compromised in their activation as an impairment of proper immune activation and not a prevention of excessive inflammation.…”

“…We believe that this is beneficial only for later time points, as in the acute phase of inflammation neutrophil activation is needed to maintain a proper immune response, otherwise leaving the host susceptible to infection 44 , 45 . Moreover, the analysis of neutrophil phenotypes using CD62L and ICAM-1 as markers for maturation 18 , 21 – 23 revealed that a significant share of CD11b expression of the whole neutrophil population was attributed to the mature CD62L-/ICAM-1 + phenotype (Suppl. Figure 1 B).…”

“…Neutrophils’ key functions are the ability to migrate to the site of injury and subsequently clear cell debris and pathogens from injured tissue, by phagocytizing and dissolving them internally by producing reactive oxygen species 18 – 20 . Recent studies showed that different neutrophil subgroups, distinguished by the expression of intercellular adhesion molecule 1 (ICAM-1, also known as CD54) and CD62L (L-Selectin), differ in their maturation and potency to exert these functions 21 – 23 .…”

Transcriptional Profiling Reveals Kidney Neutrophil Heterogeneity in Both Healthy People and ccRCC Patients

“…It is known that neutrophils exhibit highly different phenotypes and functions mainly depending on tissues and individual conditions [22][23][24][25]. Though studies reported neutrophil subpopulation/heterogeneity in the blood, bone marrow, spleen, and even in the brain, lung, and gut [26][27][28], the kidney neutrophil has been rarely studied for its extremely low frequency in this tissue. This study reported neutrophil heterogeneity in ccRCC, comparing with it in healthy condition, in a single-cell level.…”