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Open Access Research article

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

Namrata Singh1, Pamela Traisak1, Kayla A Martin2, Mariana J Kaplan3, Philip L Cohen124 and Michael F Denny124*

Author Affiliations

1 Section of Rheumatology, Temple University, 3322 North Broad Street, Philadelphia, PA 19140, USA

2 Department of Microbiology and Immunology, Temple University, 3500 North Broad Street, Philadelphia, PA 19140, USA

3 Systemic Autoimmunity Branch, Intramural Research Program, NIAMS/NIH, 10 Center Drive, Bethesda, MD 20892, USA

4 Temple Autoimmunity Center, Temple University, 3500 North Broad Street, Philadelphia, PA 19140, USA

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Arthritis Research & Therapy 2014, 16:R165  doi:10.1186/ar4681

Published: 8 August 2014

Abstract

Introduction

Patients 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.

Methods

Alterations 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.

Results

Control 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.

Conclusions

The 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.