Background/Purpose: To evaluate if interleukin-6 (IL-6) expression in the temporal artery biopsy (TAB) specimens may differentiate patients with giant cell arteritis (GCA) from those without.

Methods: 63 consecutive formalin-fixed, paraffin-embedded (FFPE) TABs performed between 2009 and 2012 from 32 patients with transmural biopsy-proven GCA, 8 patients with biopsy-negative GCA and 23 controls were retrieved. Demographic, clinical, and laboratory data at presentation and at each follow-up visit were collected. A pathologist reviewed all TABs. Immunohistochemistry was performed on 4μm FFPE tissue sections with a 1:400 dilution of rabbit polyclonal anti-human IL-6 antibody (NOVUS Biologicals Littleton, Co.) for 60’ at 37°. Slides of TAB specimens were independently assessed by five readers. IL-6 expression was graded as 0 (absent), 1 (mild), 2 (moderate) and 3 (marked). Inter-reader differences were resolved by consensus. Anti-IL6 staining was considered positive if staining was grade 2 or 3, since grade 1 was faint, sometimes difficult to differentiate from background, and showed the least degree of agreement between Readers.

Results: TAB specimens from patients with biopsy-proven GCA, biopsy-negative GCA and controls were positive for anti-IL-6 staining in 59%, 13% and 48% of cases, respectively, the difference between biopsy-proven and biopsy-negative GCA patients being significant (p = 0.04). In non-inflamed TABs, IL-6 was mainly expressed by mesenchymal cells in media and intima layers, while in inflamed TABs IL-6 was mainly expressed by mononuclear inflammatory infiltrating cells. IL-6 grade 2-3 expression was observed in all 6 patients with visual loss compared to 25 (43.9%) of 57 patients without (p = 0.011). Blindness was recorded in 2 patients with biopsy-proven GCA and 4 controls (all with a final diagnosis of non-arteritic ischemic optic neuropathy). No associations were found between IL-6 expression and demographic characteristics, GCA signs/symptoms, laboratory and histopathological TAB findings. However, there was a statistical trend (p = 0.055) of increased frequency of the halo sign at temporal artery CDS in patients with IL-6 expression grade 2-3 compared to those with IL-6 expression grade 0-1. No significant differences for the expression of IL-6 were observed between patients with and without PMR (5/8 – 62.5% – versus 6/15 – 40% -, p = 0.400) and between patients with isolated PMR and those with TAB positive GCA (62.5% vs 59%, p = 1.000).

Conclusion: Our study provides evidence that IL-6 expression does not increase the sensitivity of TAB in patients with morphologically uninflamed arteries. A search for further markers that may increase the sensitivity of TAB is warranted.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/interleukin-6-expression-in-inflamed-and-non-inflamed-temporal-arteries-from-patients-with-giant-cell-arteritis/