Background Systemic sclerosis (SSc) is an autoimmune disease characterized by dysregulation of the immune system, vasculopathy and fibrosis of the skin and internal organs. Natural Killer (CD56⁺CD3^-, NK) and NKT-like (CD56⁺CD3⁺) cells display receptors (NKR) whose expression pattern determines their cytotoxic and immune-regulatory activity. The role of NK and NKT-like cells in the dysregulation of the immune system in SSc has not been fully elucidated yet.

Objectives To improve our knowledge on the contribution of NK, NKT-like and a subset of NKT cells expressing invariant TCR (iNKT) in SSc development, we performed a broad phenotyping of NKR in the circulation of SSc patients, including subjects with pre-clinical SSc.

Methods NKR were assessed by flow cytometry using two 13-color panels on whole blood of 84 SSc patients and 20 healthy controls (HC). In particular, 15 patients with early SSc (EaSSc) without signs or symptoms of evolutive disease (2001 LeRoy and Medsger criteria¹), 24 patients with definite SSc without skin or lung fibrosis (defSSc), 26 patients with limited (lcSSc) and 19 patients with diffuse cutaneous SSc (dcSSc) (2013 ACR/EULAR classification criteria for SSc²) were included. NK degranulation in response to K562 target cells was assessed in lcSSc and dcSSc patients versus HC.

Results The number of circulating lymphocytes, NKT-like and iNKT cells - but neither CD3⁺ T nor NK cells - was reduced in dcSSc versus HC. NKp46⁺ NK cells co-expressing NKG2D and CD16 were decreased in dcSSc versus HC and EaSSc. Consistently with these observations, dcSSc exhibited lower degranulation capability. (CD57⁺)KIR⁺ and activating NKR-expressing NKT-like cells were diminished in both dcSSc and lcSSc versus HC.

Conclusions dcSSc patients showed a defective NK cytotoxicity potential, possibly due to the decreased NKp46⁺ fraction. The regulatory, cytolytic KIR⁺ NKT-like fraction was also reduced with a parallel decrease of activating receptors expression in both lcSSc and dcSSc. Overall these results point towards an impairment of NK and NKT-like cells as immune check-points in fibrotic SSc.

References

1. LeRoy EC, et al. J Rheumatol 2001.

2. van den Hoogen F, et al. Arthritis Rheum 2013.

References

Acknowledgements Supported by a grant from Gruppo Italiano per la Lotta alla Sclerodermia (GILS). MC and TR are partly supported by the VIDI laureate and Dutch Arthritis Foundation (NWO, Netherlands Institute for Science) and ERC starting grant (EU) obtained by TR. The authors would like to thank Koos Gaiser (U-DAIR, LTI, UMC Utrecht) for the technical assistance in developing the 13-color flow cytometry panels; Dr F. Montero, L. Nieto-Gligorovski and E. Gautherot (Beckman Coulter Inc, Marseille) for providing the NKG2A-PB antibody; the NIH Tetramer Facility for providing the CD1d tetramers.

Disclosure of Interest None declared