Background/Purpose: Antisynthetase syndrome (ASS) is a rare autoimmune myositis associated with interstitial lung disease (ILD) and characterized by specific anti-tRNA-synthetase autoantibodies (ARS). To date, the pathogenesis of ASS remains largely unknown and the involvement of innate immune cells, such as Natural Killer (NK) cells is poorly described. The aim of this study was to conduct the first extensive analysis of the phenotype and functional properties of NK cells in ASS.

Methods:

This monocentric study included 14 ASS patients (woman/man= 13, median age 51, range 29-77) and 7 healthy controls (w/m= 6, median age 30, range 22-42). Patients were divided into 2 groups, based on their ASS activity: active myositis (myalgia/muscle weakness with elevated creatine-kinase) or deteriorating ILD (> 10% decrease in lung vital capacity) leading to disease-modifying antirheumatic drug use, distinguished patients with active (n=6) vs inactive (n=8) ASS. NK cell phenotype was performed by flow cytometry after staining with an appropriate antibody cocktail: CD16, CD57, CD69; Natural Cytotoxicity Receptors (NKp30 and NKp44); pan-KIR, NKG2A-C-D and ILT2. Assessment of NK cell functions was performed spontaneously or after an interleukin-12 and -18 overnight stimulation, in the presence of K562 target cells, at a 1/1 ratio. Degranulation was evaluated by CD107a detection, and production of TNFα and IFNγ was measured by specific intracellular-staining. Comparisons between patient groups were performed using the Mann-Whitney test; a p-value < 0.05 was considered significant.

Results:

Myositis and ILD occurred each in 12/14 patients (median time from onset: 4 years, range 1-22) and the distribution of ARS was anti-Jo1 (n=9), anti-PL12 (n=4) and anti-PL7 (n=1). Patients (n=12) were receiving stable doses of steroids (n=10, median 10 mg/d, range 5-20) and/or immunosuppressive drugs, including Methotrexate (n=5), Mycophenolate Mophetil (n=3) or Hydroxychloroquine (n=3). Patients with ASS had a normal percentage of NK cells among circulating lymphocytes (9.6 ± 6.4%) but a dramatically low absolute count: 89 ± 73/mm³ (vs controls: 221 ± 100/mm³, p=0.02). NK cells from ASS patients were indistinguishable from those of controls in term of the cell-surface expression of NK receptors. However, NKp30, a receptor involved in NK cell-Dendritic cell crosstalk, was decreased in active ASS patients as compared to both inactive patients and controls (50.3 ± 25.7% vs 80.6 ±11.2% and 85.4 ± 7.4, p=0.03 and 0.01, respectively).

Functional activities revealed no differences between ASS patients and controls, regarding both spontaneous degranulation capacities (29.7 ± 13.4% vs 21.8 ± 9.4%, p=0.14) and intracellular-TNFa production after stimulation (4 ± 4.4% vs 6,2 ± 6.4%, p=0.25). Conversely, IFNg production was dramatically decreased after stimulation in ASS patients vs controls (12.7 ± 14.0% vs31.3 ± 12.9%, p=0.01) and seemed not related to treatments.

Conclusion:

Although quantitatively decreased, NK cells mainly displayed a normal phenotype in ASS. However, NK cells from patients with ASS had a significantly decreased capacity to produce IFNg, suggesting that they may play an immune regulatory role in favor of a TH2/TH1 imbalance.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/decreased-number-of-circulating-nk-cells-and-dramatic-lack-of-ifn-gamma-production-in-patients-with-antisynthetase-syndrome/