Characterization of Circulating Low-Density Neutrophils Intrinsic Properties in Healthy and Asthmatic Horses

Abstract

Low-density neutrophils (LDNs) are a subset of neutrophils first described in the bloodstream upon pathological conditions, and recently, in the blood of healthy humans. LDNs may have an enhanced pro-inflammatory (low-density granulocytes, LDGs) or an immunosuppressive (Granulocytic myeloid-derived suppressor cells, G-MDSCs) profile. Whether these characteristics are specific to LDNs or related to disease states is unknown. Thus, we sought to investigate the properties of LDNs in both health and disease states, and to compare them to those of autologous normal-density neutrophils (NDNs). We studied 8 horses with severe equine asthma and 11 healthy animals. LDNs were smaller and contained more N-formylmethionine-leucyl-phenylalanine receptors than NDNs, but the myeloperoxidase content was similar in both cell populations. They also had an increased capacity to produce neutrophil extracellular traps, and were more sensitive to activation by phorbol-12-myristate-13-acetate. This profile is suggestive of LDGs. These characteristics were similar in both healthy and diseased animals, indicating that these are intrinsic properties of LDNs. Furthermore, these results suggest that LDNs represent a population of primed and predominantly mature cells. This study is the first to characterize LDNs in health, and to compare their properties with those of NDNs and of animals with a naturally occurring disease.

Neutrophil Diversity in Health and Disease

“…In view of several species-specific differences that might have a profound impact on the phenotypic and functional plasticity of neutrophils, human and mouse studies are separately discussed, highlighting similarities and differences between current findings in the two species. There is emerging evidence of heterogeneous populations of neutrophils in other organisms, such as the rhesus macaque [10], zebrafish [11,12], and horse [13], but these are beyond the scope of our discussion.…”

Update on Neutrophil Function in Severe Inflammation

“…These cells include cells both segmented and banded nuclei as well as myelocyte-like progenitor cells ( 85 ). LDNs were first reported in systemic lupus erythematosus (SLE), rheumatoid arthritis and rheumatic fever ( 86 ). They are now also recognized as being elevated in cancer and are in some studies associated with tumor progression ( 87 ).…”

Extracellular Traps: An Ancient Weapon of Multiple Kingdoms

“…Although their MPO content was the same, LDN were found to be more sensitive to PMA, and thus showed an increased capacity to produce NETs [69]. This finding could be important, since LDN exhibit an increased synthesis of TNFα, IL-6, IL-8 and IFN1 and are found in the blood of horses suffering from lupus and cancer, as well as systemic and local infections [69]. These data correlate well with the finding by Villanueva and colleagues, who associated elevated NET-forming capacity of LDN to lupus [138].…”

“…NETosis was prevented by the addition of seminal plasma (SP) [68], which also reduced the binding between spermatozoa and neutrophils. Low-density neutrophils (LDN), found in the PBMC layer after density centrifugation, displayed a higher rate of Fmlp receptors on their surface as compared with normal density neutrophils [69]. Although their MPO content was the same, LDN were found to be more sensitive to PMA, and thus showed an increased capacity to produce NETs [69].…”

“…Low-density neutrophils (LDN), found in the PBMC layer after density centrifugation, displayed a higher rate of Fmlp receptors on their surface as compared with normal density neutrophils [69]. Although their MPO content was the same, LDN were found to be more sensitive to PMA, and thus showed an increased capacity to produce NETs [69]. This finding could be important, since LDN exhibit an increased synthesis of TNFα, IL-6, IL-8 and IFN1 and are found in the blood of horses suffering from lupus and cancer, as well as systemic and local infections [69].…”