Background/Purpose:

The phenotype of patients afflicted by deficiency of adenosine deaminase 2 (DADA2) due to mutations in CECR1encoding ADA2 protein shares many features with idiopathic polyarteritis nodosa (PAN), including abundant neutrophilic infiltration in affected tissues. Immune cell responses following treatment with TNF inhibitors and the specific role of neutrophils were studied in a family consisting of 2 children with DADA2 and several family members afflicted by various autoimmune diseases including idiopathic PAN.

Methods:

Candidate-gene sequencing of the CECR1gene was performed in 2 children who had lacunar infarcts, livedoid rash and biopsy-proven vasculitis. Histopathology characterization was performed on affected skin and small bowel tissues. Neutrophils and low-density granulocytes (LDGs) were isolated during active disease. Neutrophil extracellular traps (NETs) were quantified and visualized by fluorescence microscopy. Neutrophils were incubated with graded concentrations of adenosine +/- ADA2 enzyme and resultant NET formation was quantified. Evaluations were conducted during active disease and 4 months later during disease remission after treatment with etanercept. Immune cell subsets before and after treatment were quantified by multi-panel flow cytometry. 

Results:

Both children were compound heterozygotes for G358R and G47R mutations in the CECR1 gene. The mother was a carrier for G358R mutation and had a history of unexplained lacunar infarct at age 45. A maternal great grandmother had a history of biopsy-proven PAN onset at age 60, and a maternal great uncle had a history of autoimmune colitis and livedo reticularis. The father was a carrier for G47R mutation and had a history of Guillian-Barré syndrome. Fibrinoid necrosis of medium-sized blood vessels, intravascular thrombi, and dense perivascular infiltrates of netting neutrophils and macrophages were visualized in affected skin and small bowel sections from children. Immunohistochemistry showed aggregates of MPO, CD163 and CD3 positive cells in the deep dermis and perivascular region. An abundance of circulating LDGs prone to spontaneous NET formation was observed during active disease and also in clinically unaffected heterozygous carriers of CECR1 mutation. LDG numbers normalized when remission was achieved using anti-TNF agents. Various concentrations of adenosine [0.2, 0.5, 16 µM] stimulated robust NET formation, and this was inhibited by addition of recombinant ADA2. Following treatment with etanercept, there were decreases in CD14⁺/CD16⁺ monocytes (8% vs 2%), increases in memory T_reg cells (12% vs 23%), activated T_reg(2% vs 7%) and B cells (2% vs 19%).

Conclusion:

Neutrophils may play pathogenic roles in DADA2. LDGs and NETs are observed during active disease in children with DADA2 and their parents.  Deficiency of ADA2 may increase risk for adenosine-induced NET formation, which is a novel mechanism of NETosis. Alterations in the adenosine-mediated signaling pathway may contribute to the pathogenesis of DADA2.  The autoimmunity observed in this family suggests that carriers of CECR1gene mutation may have increased risk for autoimmune diseases and that DADA2 and idiopathic PAN may be genetically related.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/role-of-adenosine-and-neutrophils-in-inflammation-associated-with-mutations-in-cecr1-gene/