Background The etiology of spondyloarthritis (SpA) is unknown but seems to indicate a link between genetic and environmental factors. Many GWAS studies demonstrated a strong association between IL23R gene and the disease. Moreover, several IL-17 producing lymphocyte populations characterized by the expression of CCR6 (TD4+, TCD8, Tγδ and ILC) are involved in pathophysiolgy of SpA.
Objectives The aim of the study was to identify cells population involved in the disease development:
- By comparing simultaneously cells population TCD4+, TCD8+, Tγδ et ILC (and sub-population ILC3) in patients and healthy controls.
By analysing simultaneously the expression of IL23R and CCR6 by TCD4+, TCD8+, Tγδ and ILC in patients
Methods Patients: 10 patients aged from 18 to 50, fulfilling the ASAS criteria and presenting a BASDAI>40 were recruited from diagnosis (between February to may 2015), and compared to 7 healthy subjects paired according to their age.
Methods: The cell analysis was realized by hyperspectrale cytrometry (Sony SP6800®) after cell staining of the mononuclear cells. This emerging technology combines optical spectroscopy and flow cytrometry. The panel used included 13 colours (BV421 conjugated to anti-CD127, V450 conjugated to anti-CD3, V500 conjugated to anti-CD4, BV570 conjugated to anti-CD8, BV605 conjugated to anti-CD62L, BV650 conjugated to anti-CD117, BV711 conjugated to anti-CCR6, BV786 conjugated to anti-NKp46, Percp Cy5.5 conjugated to anti-CD161, PE conjugated to anti IL23R, PE-CF594 conjugated to anti-CRTH2, PE-Cy7 conjugated to anti-TCRgd).
Results The quantitative analysis of cell populations did not show any significant difference between patients and controls: TCD4+ (p=0.2), TCD8+ (p=0.93), Tγδ (p=0.52), ILC (p=0.46) et ILC3 (p=0.71). These results suggested that the functional properties of immune cells (rather than their frequencies) were involved in the disease process. We have demonstrated TCD4+, TCD8+, Tγδ and ILC, all expressed IL23R as well as CCR6. However, we did not notice any difference in expression of these two markers between patients and controls. Then, we showed that in SpA, the level of CCR6 expression was higher in TCD4+ lymphocyte populations (p=0.0031). Similarly, the level of expression of IL23R was higher in TCD8+ lymphocyte (p<0.0001).
Conclusions These preliminary results suggest SpA development does not result from the increase of specific cell populations but rather from the modification of the functional properties of immune cells. The increase of CCR6 expression in TCD4+ and IL23R in TCD8+ shows that these two cell populations take a major part in the disease. In spite of recent datas concerning Tγδ and ILC3, our results did not highlight a major participation of these cells. These prelimanry data need to be confirmed in a larger cohort of patient.
Acknowledgement Département d'immunologie Unité “ immunorégulation ”, CNRS URA 1961 Institut Pasteur Paris
Disclosure of Interest None declared