FRI0211 The role of NKG2D, CX3CR1 and TLR4 in the pathogenesis of giant cell arteritis
Authors: J. Al-Massad, C. Dejaco, C. Duftner, T. Ness, H. Haller, M. Schirmer, A.D. Wagner
Journal: Annals of the Rheumatic Diseases (2013)

<h3>Background</h3> Pattern recognition receptors like NKG2D [1] and TLR4 [2] together with chemokine receptors like CX3CR1 [3] are important mediators of innate immunity. <h3>Objectives</h3> The study was performed to assess the expression of NKG2D, CX3CR1 and TLR4 on T-cells in temporal arteries from patients with giant cell arteritis (GCA) and to compare findings with results from peripheral blood analysis. <h3>Methods</h3> Temporal artery biopsies were obtained from 19 patients diagnosed with GCA and from 9 patients without GCA. For analysis of peripheral blood T-cells from consecutive patients with GCA (n=16) and PMR (n=78) were investigated. Immunohistochemical staining was performed on paraffin-embedded temporal arteries using anti-CD3, anti-CD4, anti-CD8 and anti-NKG2D (monoclonal antibodies) as well as anti-CX3CR1 and anti-TLR4 (polyclonal antibodies) according to a routine protocol. For assessment of circulating T-cells anti-CD4, anti-CD8, anti-CD28, anti-NKG2D, anti-CX3CR1 and anti-TLR4 mAbs were used and cells were analyzed by flow cytometry. Statistical analysis was performed using SPSS. <h3>Results</h3> Immunohistochemical analysis of temporal arteries confirmed CD4<sup>+</sup> T-cells as the dominant T-cell population in GCA showing a ratio of 70/30 compared with CD8<sup>+</sup> T-cells. Most pronounced expression of NKG2D was shown in the media and adventitia compared to intima. Immunofluorescence double-staining confirmed the expression of NKG2D on every fifth CD3<sup>+</sup> T-cell especially in the adventitia near the vasa vasorum. The expression of NKG2D showed no dependence on a therapy with glucocorticoids over time. The chemokine receptor CX3CR1 and the toll-like receptor TLR4 accumulated in the adventitia of temporal arteries. Likewise CX3CR1<sup>+</sup>CD3<sup>+</sup> and TLR4<sup>+</sup>CD3<sup>+</sup> T-cells were detected on every fifth and third T-cell, respectively. Biopsies of the control group compared to the GCA group showed statistically significant lower numbers of NKG2D-, CX3CR1- and TLR4-positive cells as determined by student's t-test. In peripheral blood analysis we found NKG2D, CX3CR1 and TLR4 particularly on senescent CD4<sup>+</sup>CD28<sup>-</sup> T-cells (NKG2D: 23.1±24.0% out of CD4<sup>+</sup>CD28<sup>-</sup>cells, p&lt;0.001 compared to CD4<sup>+</sup>CD28<sup>+</sup> cells; CX3CR1: 62.7±22.8%, p&lt;0.001 TLR4 4.7±11.1%, p&lt;0.001) whereas expression was negligible on CD4<sup>+</sup>CD28<sup>+</sup>. In the CD8<sup>+</sup> T-cell subset, NKG2D was expressed in &gt;95% of cells with comparable levels between CD8<sup>+</sup>CD28<sup>-</sup> and CD8<sup>+</sup>CD28<sup>+</sup> T-cells. CX3CR1 was present in the CD8<sup>+</sup>CD28<sup>-</sup> subset only (65.8±20.2%, p&lt;0.001 compared to CD8<sup>+</sup>CD28<sup>+</sup>cells) and TLR4 was not expressed on CD8<sup>+</sup> T-cells. <h3>Conclusions</h3> The expression of NKG2D is indicative of co-stimulative activity. The finding of CX3CR1 on T-cells close to vasa vasorum might be in accordance with leucocyte extravasation. The expression of TLR4 on T-cells most likely with the loss of the co-stimulatory surface glycoprotein CD28 represents a link between the adaptive and the innate immune system and might be indicative for an alternative signaling pathway in the pathophysiology of GCA. <h3>References</h3> Maasho K et al. J Immunol, 2005; 174: 4480-4484. Raffeiner B et al. Arthritis Res Ther. 2005; 7:1412-1420. Umehara H et al. Arterioscler Thromb Vasc Biol. 2004; 24: 34-30. <h3>Disclosure of Interest</h3> None Declared