Inflammatory cytokines in normal human tears

To elucidate inflammatory cytokine levels in normal human tears, we investigated the concentrations of interleukin-1alpha (IL-1alpha), interleukin-1beta (IL-1beta), interleukin-6 (IL-6), and interleukin-8 (IL-8) both in basal tears and reflex tears of normal healthy eyes.

Tear samples were collected from 270 healthy, normal volunteers with no past history of ocular surface disease; the total number of eyes was 295. All tear samples were collected in graduated disposable microcapillaries from the conjunctival cul-de-sac. Reflex tear stimulation was carried out by inserting an applicator into each volunteer's nose. Cytokine levels in basal tears and reflex tears were determined by ELISA. Tears were not diluted, and pooled samples were used for the cytokine assays.

In basal tears, the concentrations of IL-1alpha, -1beta, -6 and -8 were 10.9 +/- 1.2, 12.9 +/- 2.3, 226.2 +/- 29.6 and 731.4 +/- 116.2 pg/ml, respectively. In reflex tears, IL-1beta was not detectable, and the concentrations of IL-1alpha, -6 and -8 were 9.3 +/- 2.7, 11.6 +/- 1.6 and 276.1 +/- 47.5 pg/ml respectively. IL-1beta, -6 and -8 levels in reflex tears were significantly lower than those in basal tears, except for IL-1alpha.

In the present study, the normal concentration range of inflammatory cytokines in human basal tears was clarified, as a baseline for further studies to examine the levels of these cytokines in tears during disease states.