IgA-Expressing Cells at the Human Ocular Surface and Reduced Tear IgA2 Abundance in Schirmer Strip Extracts from Patients with Dry Eye Disease and Primary Sjögren’s Syndrome

This study investigated the distribution of IgA-expressing cells in human ocular tissues and IgA subclass profiles in Schirmer strip extracts from patients with dry eye disease (DED) and primary Sjögren’s syndrome (pSS). Immunofluorescence staining was performed on paraffin-embedded lacrimal gland, conjunctival, and corneal tissues from body donors. Independently, Schirmer strip extracts from healthy controls (n = 18), patients with DED (n = 75), and patients with pSS (n = 10) were analyzed. Total protein concentrations were determined using a bicinchoninic acid assay, while total IgA, IgA1, and IgA2 were quantified by ELISA and normalized to total protein. CD38+ and CD38− IgA-expressing cells were detected in the lacrimal gland and conjunctival stroma, with IgA1-expressing cells predominating over IgA2-expressing cells. No IgA-positive cells were detected in the examined corneal sections. Total protein concentrations were lower in pSS than in DED. Normalized IgA2 abundance was reduced in both DED and pSS compared with controls, while normalized total IgA was additionally reduced in pSS. Unnormalized extract concentrations showed broadly similar patterns. These independent findings demonstrate differences in recovered IgA subclass profiles, although differences in collection materials and patient characteristics preclude attributing these alterations exclusively to the underlying diseases.