Survey of cytokines in normal canine tears by multiplex analysis: A pilot study

The purpose of this pilot study was to use a multiplexed assay to measure cytokines in normal stimulated canine tears.

25 healthy dogs were included in the study. Stimulated tears were collected in capillary tubes from the right (OD) and left (OS) eyes and stored at -80 °C until batch sample analysis was performed. The samples were analyzed utilizing Luminex^® canine-validated multiplex beads on a Bio-Rad multiplex analyzer for IL-2, IL-6, IL-7, IL-8, IL-10, TNF-α, and IFN-γ. Based upon previous human studies, tears were initially evaluated at a 1:10 dilution. Eight random samples were later re-analyzed without dilution.

Diluting the samples 1:10 rendered all analytes undetectable except IL-8. A repeat analysis of eight randomly selected undiluted samples still demonstrated very low cytokine levels except for IL-8 (16/16 eyes; 2254 ± 1677 pg/ml OD, 1095 ± 786.8 pg/ml OS); and IFN-γ (15/16 eyes; 13.37 ± 13.08 pg/ml OD,16.08 ± 19.4 pg/ml OS).

This pilot study is the first to analyze cytokines in canine tears. This study demonstrated that IL-8 is consistently detected in both diluted and undiluted samples, but undiluted samples may be superior to 1:10 diluted samples for evaluation of other cytokines in canine tears.