Correlations between Tear IP-10 and other Biomarkers in Normal and Dry Eye Patients

Abstract

Purpose: : This lab previously reported high levels of IFN-gamma-inducible protein (IP-10) in normal tear fluid using a Bio-Rad 27-Plex cytokine assay. Because tear IP-10 has been found by others to increase under pro-inflammatory conditions, correlations between tear IP-10 and other biomarkers were investigated in normal and dry eye patients.

Methods: : Non-stimulated tear samples were collected by micropipette from normal (n = 7) and dry eye (n = 14) patients. Inclusion criteria for the dry eye group: OSDI score (≥ 18) plus one or more of the following: NIBUT ≤ 10s, fluorescein or Lissamine green score >3, Schirmer 1 test ≤ 10 mm/5 min). Tear samples were stored in assay buffer at -80°C prior to assay on a Luminex 200 system. The 27-Plex-based tear IP-10 assay was separately validated by running matching tear samples on a WHO-calibrated single analyte ELISA (DiaClone, France).

Results: : The correlation between ELISA and 27-Plex assay levels for IP-10 was moderate, but significant, and the multiplex assay consistently reported higher IP-10 values. IP-10 levels in the dry eye group (25.1 ± 5.3 ng/mL) did not correlate with IFN-γ (p > 0.46), but correlated significantly with IL-1RA (p<0.05) and IL-7 (p<0.01). As with earlier studies, normal patients showed high tear IP-10 levels (51.9 ± 14.7 ng/mL), that also did not correlate with IFN-γ (p>0.13). However, several normal tear biomarkers correlated significantly with IP-10: IL-1β (p<0.04), IL-7 (p<0.03), IL-9 (p<0.01), IL-10 (p<0.01), IL-12p70 (p<0.01), IL-13 (p<0.01), IL-17 (p<0.05) and PDGF-bb (p<0.01).

Conclusions: : High levels of IP-10 in tears have been confirmed by other groups. However, the finding in the current study of higher tear IP-10 levels in normal patients differs from other reports. A lack of correlation between tear IP-10 and IFN-γ in both normal and dry eye groups is surprising, given that IP-10 correlated significantly with other specific biomarkers in each group. Interference in the 27-Plex assay may be responsible for exaggerated tear levels. However, the current findings suggest that the anti-angiogenic properties of tear IP-10 may contribute to normal ocular surface immune privilege.

Keywords: cytokines/chemokines