Genomic alterations in abnormal neutrophils isolated from adult patients with systemic lupus erythematosus

Abstract

IntroductionPatients with systemic lupus erythematosus (SLE) have an abnormal population of neutrophils, called low-density granulocytes (LDGs), that express the surface markers of mature neutrophils, yet their nuclear morphology resembles an immature cell. Because a similar discrepancy in maturation status is observed in myelodysplasias, and disruption of neutrophil development is frequently associated with genomic alterations, genomic DNA isolated from autologous pairs of LDGs and normal-density neutrophils was compared for genomic changes.MethodsAlterations in copy number and losses of heterozygosity (LOH) were detected by cytogenetic microarray analysis. Microsatellite instability (MSI) was detected by capillary gel electrophoresis of fluorescently labeled PCR products.ResultsControl neutrophils and normal-density SLE neutrophils had similar levels of copy number variations, while the autologous SLE LDGs had an over twofold greater number of copy number alterations per genome. The additional copy number alterations found in LDGs were prevalent in six of the thirteen SLE patients, and occurred preferentially on chromosome 19, 17, 8, and X. These same SLE patients also displayed an increase in LOH. Several SLE patients had a common LOH on chromosome 5q that includes several cytokine genes and a DNA repair enzyme. In addition, three SLE patients displayed MSI. Two patients displayed MSI in greater than one marker, and one patient had MSI and increased copy number alterations. No correlations between genomic instability and immunosuppressive drugs, disease activity or disease manifestations were apparent.ConclusionsThe increased level of copy number alterations and LOH in the LDG samples relative to autologous normal-density SLE neutrophils suggests somatic alterations that are consistent with DNA strand break repair, while MSI suggests a replication error-prone status. Thus, the LDGs isolated have elevated levels of somatic alterations that are consistent with genetic damage or genomic instability. This suggests that the LDGs in adult SLE patients are derived from cell progenitors that are distinct from the autologous normal-density neutrophils, and may reflect a role for genomic instability in the disease.Electronic supplementary materialThe online version of this article (doi:10.1186/ar4681) contains supplementary material, which is available to authorized users.

Human neutrophils in the saga of cellular heterogeneity: insights and open questions

“…This is supported by other findings showing that proinflammatory LDNs/LDGs of SLE patients, differently from autologous NDNs, display elevated numbers of somatic alterations that are indicative of genetic damage or genomic instability (83). If so, SLE LDNs/LDGs might be abnormal neutrophils deriving from cell progenitors distinct from autologous NDNs, as concluded by the authors of these studies (83). Unlike immunosuppressive LDNs/G-MDSCs, proinflammatory LDNs/LDGs have been isolated from PBMCs by negative selection, utilizing a so-called 'LDG isolation cocktail' composed by a mixture of antibodies recognizing T, B, NK cells, and monocytes as well as residual red blood cells [namely CD3, CD7, CD19, CD79b, CD56, MHC class II, CD86, and CD235 respectively (78)].…”

“…While the phenotype of proinflammatory LDNs/LDGs identified in psoriasis, AAV or CGD patients has been poorly investigated , it is currently thought that SLE LDNs/LDGs may consist of incompletely matured neutrophils prematurely released from the bone marrow in response to yet uncharacterized stimuli . This is supported by other findings showing that proinflammatory LDNs/LDGs of SLE patients, differently from autologous NDNs, display elevated numbers of somatic alterations that are indicative of genetic damage or genomic instability . If so, SLE LDNs/LDGs might be abnormal neutrophils deriving from cell progenitors distinct from autologous NDNs, as concluded by the authors of these studies .…”

On the origin of low-density neutrophils

“…In SLE the presence of LDNs has been established by multiple studies 25,45,39,46 . These neutrophils are believed to have a contribution to the pathogenesis of SLE by an enhanced capability to produce type I IFNs and release neutrophil extracellular traps 39,47 .…”

Phagocyte activity in the peripheral blood of pregnant women with systemic lupus erythematosus and in the cord blood of their newborns

“…Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by tolerance loss to native nucleic acids, hyperactivity of T‐ and B‐cells, production of antibodies, deposition of immune complexes and multisystemic damage . Different types of innate immune cells exhibit anomalous properties in SLE . Genetically mediated abnormal activation of monocytes and neutrophils is currently assumed to be an important factor in SLE pathogenesis.…”

“…1,2 Different types of innate immune cells exhibit anomalous properties in SLE. 3,4 Genetically mediated abnormal activation of monocytes and neutrophils is currently assumed to be an important factor in SLE pathogenesis. Monocyte defects in SLE are manifested through deteriorations in surface marker expression, phagocytosis and cytokine production.…”