Phenotype of Tear Leukocytes in Seasonal Ocular Allergy and Their Potential Impacts on Ocular Surface Inflammation

Under normal physiological conditions, tear polymorphonuclear neutrophils (PMNs) collected from the ocular surface after prolonged eye closure at night exhibit a distinct phenotype from circulating PMNs. While leukocytes have been previously observed in tears of individuals suffering from ocular allergies, limited knowledge exists on tear PMNs activation. This pilot study aims to investigate the phenotype of tear PMNs collected from participants with seasonal ocular allergy.

Ten participants experiencing symptoms of ocular allergy were recruited and age- and gender-matched with 10 healthy participants. Participants were asked to collect cells using a gentle eyewash protocol immediately following a full night of sleep in the morning on Day 1 and at the end of the day on Day 2. After cell count, tear leukocytes were activated with N-Formyl-Methionyl-Leucyl-Phenylalanine (fMLP) or left unstimulated. Samples were stained with antibodies against degranulation markers (CD66b, CD63), adhesion markers (CD11b, CD54), eosinophil marker (CD193), and aging marker (CD184), and analysed by flow cytometry.

Significantly more tear leukocytes were collected after a night of sleep from participants with ocular allergy compared to healthy participants (p = 0.024), while there was no difference in late afternoon collections. Tear PMNs from ocular allergy patients also exhibited a less activated baseline phenotype but a higher activation potential in response to fMLP.

This study indicates that the ocular environment in seasonal allergy affects the recruitment and activation of tear PMNs. Further research is needed to understand the role of tear leukocytes in ocular surface homeostasis and inflammation.