Inflammatory markers in tears help detect COVID-19

Elevated levels of various proinflammatory cytokines in tears can indicate active SARS-CoV-2 infection and the presence of the virus in the conjunctiva, a recent study has found.

The study included 232 patients with symptomatic coronavirus disease 2019 (COVID-19), in whom ocular viral infection was confirmed through positive swabs on RT-PCR testing. Tear films were collected and subjected to magnetic bead assays to measure levels of inflammatory markers including tumour necrosis factor-α (TNF-α), interferon-γ (IFN-γ), granulocyte-macrophage colony-stimulating factor (GM-CSF), and interleukins (IL)-5, -8, and -6.

Compared with patients who had negative conjunctival swab results, those who were positive for ocular viral infection showed a significantly higher level of TNF-α in tear film samples (2.05 vs 1.18 pg/mL; p=0.047). Similarly, tear GM-CSF levels were elevated in these patients (0.50 vs 0.37 pg/mL; p=0.004).

In addition, IFN-γ in tear film appeared to be a significant indicator of ocular infection (1.72 vs 1.17 pg/mL; p=0.04), as did IL-5 (0.21 vs 0.15 pg/mL; p=0.048) and IL-8 (135.32 vs 82.72 pg/mL; p=0.04).

Moreover, IL-1β tear film concentrations were significantly correlated disease severity (p=0.035) and were higher in those with pneumonia complicating COVID-19 (0.52 vs 0.28 pg/mL; p=0.0041).

“The activation of ocular immune responses observed in the group of symptomatic COVID-19 patients with positive conjunctival swab results may indicate the presence of active infection with SARS-CoV-2 and might carry some important therapeutic implications,” the researchers said.

“Further molecular studies are needed to confirm or refute these results. In particular, more studies are warranted to detect the existence of SARS-CoV-2 in different ocular tissues to clarify the existing ambiguities,” they added.