Comparison of tear proteome in allergic rhinoconjunctivitis patients and controls with respect to pollen season

Tear fluid comprises electrolytes, lipids, mucins and proteins among other components [1]. Tear composition reflects the physiological condition of underlying tissue but can be altered in disease related to the eye or other organs and systemic diseases like diabetes [2]. Several tear proteomic studies for diseases other than allergic rhinoconjunctivitis exist proofing the feasibility of proteomic approaches to tear fluid [3-6]. This article is protected by copyright. All rights reserved.

To the Editor, Tear fluid comprises electrolytes, lipids, mucins, and proteins among other components. 1 Tear composition reflects the physiological condition of underlying tissue but can be altered in disease related to the eye or other organs and systemic diseases such as diabetes. 2 Several tear proteomic studies for diseases other than allergic rhinoconjunctivitis exist proofing the feasibility of proteomic approaches to tear fluid. [3][4][5][6] Twenty-one individuals (8 male, 13 female) with a mean age of 33 years (SD: 8.3 years) were prospectively included in the study group comprising 10 (48%) patients with allergic rhinoconjunctivitis (AR) and 11 (52%) healthy controls (HC). From patients with AR, tear fluid was collected in pollen season according to their sensitization pattern and the airborne pollen exposure (pollen counts) and symptoms present. On the same day, the same number of healthy controls was recruited from the outpatient department at the same time to have the same natural pollen exposure. The same patients and controls were recalled on the same day out of season. The day depended on the respective patients with AR. They must not have had symptoms, and natural pollen exposure must have been diminished during the out of season visit. Tear fluid was collected and sent to LC-MS/ MS mass spectrometry. For detailed methods, please see Data S1.
In total, 90 proteins could be identified and quantified in tear fluids. Given the requirement that the protein was filtered for 70% valid values of samples in at least one group, 22 different proteins were further analyzed (Table S1, online). Comparing seasonal and group differences, six proteins showed significantly different abundances ( Figure 1).
Lactotransferrin was the only protein that was significantly less abundant (1.2-fold) out of season in patients with allergic rhinoconjunctivitis than in season ( Figure 1).
In contrast, in healthy controls, eight proteins were significantly altered in abundance out of season as compared to in season ( Figure 1). Three proteins were found to be more abundant in HC out of season. On the other hand, five proteins had decreased abundance out of season.
Out of season, four different proteins were significantly more abundant in AR than in HC. In season, three proteins were significantly more abundant in AR than in HC ( Figure 1).
The majority of pathways over both groups and seasons were related to the immune system ( Figure S1). Others were transport of small molecules, vesicle-mediated transport, metabolism of proteins, disease, and hemostasis.
Here, we investigated the tear fluid proteome of patients with allergic rhinoconjunctivitis and controls following them in and out of pollen season. Lipocalin-1/LCN1 was found to be significantly more abundant in AR compared to HC in season and was significantly less abundant in HC in season compared to out of season. Lipocalins have been described for various functions in tear fluid including tear viscosity but were thus far not brought into context with allergic rhinoconjunctivitis, but with keratoconus. 6,13 Their reduced abundance in season could be a reaction toward pollen stress in HC lowering tear viscosity enhancing clearing of allergens from the conjunctiva which was not observed in AR.
Zinc-alpha-2-glycoprotein/AZGP1 and zymogen granule protein 16 homolog B/ZG16B were both significantly upregulated in AR out of season compared to HC and in season in HC compared to out of season. AZGP1 has similarity to MHC class I antigen-presenting molecules and may have a role in immune response in tear fluid. 14 ZG16B was significantly elevated in reflex tears. 15

CONFLI CTS OF INTEREST
The authors declare that they have no conflicts of interest.