Interleukin 6 and its soluble receptor are elevated in aqueous humor of patients with uveitis

To determine the levels of interleukin 6 (IL-6) and its soluble receptor (sIL-6R) in the aqueous humor (AH) of patients with different uveitis entities.

AH and serum samples were collected from 35 patients (39 eyes) who underwent surgery for uveitis complications and from 10 controls (senile cataract). In the studied group, seven patients had HLA-B27(+) anterior uveitis, two had Fuchs' heterochromic iridocyclitis, 12 had chronic anterior uveitis of unknown etiology, and in the remaining 14 the causative agent was exogenous. The cytokine and receptor levels were measured by enzyme-linked immunosorbent assay (ELISA).

In controls, the median IL-6 level in AH was higher than that in corresponding sera (40.4 pg/ml and 5.2 pg/ml, respectively). In contrast, sIL-6R showed an inverse relation: there were less sIL-6R in control AH than in control sera (378.9 pg/ml and 52749.0 pg/ml, respectively). The same qualitative relationship was observed in patients with uveitis. Quantitatively, in comparison to controls, elevated levels of IL-6 and sIL-6R were found in AH of patients with uveitis. As expected, the maximal IL-6 and sIL-6R values were observed in the patients with uveitis of exogenous etiology (1558.3 and 1326.2 pg/ml, respectively). sIL-6R was also significantly elevated in AH of patients with HLA-B27( +) anterior uveitis (p<0. 01). In all individuals under study, sIL-6R levels in AH samples were 2-10 times higher than IL-6 levels. In serum samples, sIL-6R level were 10000 times higher than corresponding IL-6 values.

The results confirmed the role of IL-6 in intraocular inflammation and gave new information regarding the presence of its sR in normal and inflamed eyes. Low levels of sIL-6R in AH compared to those found in serum suggest the presence of active local regulatory mechanisms that require further investigation.