Background/Purpose: Recent research has increased the appreciation of the contributions of neutrophils to systemic lupus erythematosus (SLE).  An abnormal circulating pool of granulocytes has been associated with certain disease manifestations, and we previously developed techniques to isolate these low-density granulocytes (LDGs) from the blood of SLE patients.  While LDGs express surface markers consistent with mature neutrophils, their nuclear morphology suggests an immature phenotype.  This pattern of mature neutrophils possessing an abnormal nuclear morphology is frequently observed in patients with alterations in granulocyte development, suggesting that neutrophil differentiaton may be disrupted in SLE patients.

Methods: Because disrupted neutrophil development is frequently associated with genomic alterations, we compared genomic alterations in autologous pairs of LDGs and normal-density neutrophils.  Somatic alterations were detected by cytogenetic microarray analysis of genomic DNA extracted from LDGs and neutrophils from 13 female SLE patients, as well as neutrophil samples from 9 age-matched healthy female donors.  The Affymetrix 2.7M Cytogenetics Microarray chip was used to assess both copy number state and heterozygosity across the genome.  For each SLE patient we compared genomic DNA from LDGs to DNA from autologous neutrophils.  Variations present in both samples are inherited, while alterations found exclusively in the LDG sample represent the acquisition of additional somatic alterations.

Results: The SLE normal density neutrophils and healthy donor neutrophils had similar levels of copy number variations, most of which corresponded to known variants.  In contrast, the LDG samples from SLE patietns had a two-fold increase in copy number alterations relative to either autologous normal-density neutrophils or healthy controls.  The elevation in genomic copy number variations in the LDG samples included an increased incidence of both duplications and deletions.  These LDG somatic alterations were found in 6 of the 13 patients.  Thus, the LDGs isolated from a subset of SLE patients displayed evidence of genomic instability as determined by alterations in copy number.  Moreover, these genomic alterations occurred preferentially on certain chromosomes, as opposed to random distribution across the genome.  No correlation between genomic instability and the use of immunosuppressive drugs, disease activity or manifestations was observed.

Conclusion: In a subset of SLE patients, the LDGs show an elevated level of genomic alterations that is consistent with genetic damage or instability.  These alterations occur in discrete chromosomal intervals, suggesting these regions reflect an increased propensity for damage or that the alteration confers a selective advantage to the affected cell.  Whether the inflammatory environment present in SLE patients promotes these genetic alterations, or whether it is an intrinsic property of the SLE genome, remains to be determined.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/abnormal-neutrophil-development-in-human-systemic-lupus-erythematosus/