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.
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.
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