Conjunctival Intraepithelial Lymphocytes, Lacrimal Cytokines and Ocular Commensal Microbiota: Analysis of the Three Main Players in Allergic Conjunctivitis

Abstract

Conjunctival intraepithelial lymphocytes, tear soluble molecules and commensal microbiota have important roles in the ocular mucosal immune response in healthy and diseased subjects. For the purpose of this study, the cellular and microbial populations of the conjunctiva and the lacrimal soluble molecules were analyzed to find the main biomarkers in allergic conjunctivitis. A total of 35 healthy subjects, 28 subjects with seasonal allergic conjunctivitis and 32 subjects with perennial allergic conjunctivitis were recruited to obtain peripheral blood, conjunctival brush cytology, tear fluid and microbiota samples. Flow cytometry for lymphocytes, multiplex bead assays for cytokines and high-throughput DNA sequencing for microbiome analysis were used. For perennial allergic conjunctivitis, an increased proportion of Th2 and NKT lymphocytes was found, while CD3+TCRγδ+ lymphocytes and double negative MAIT cells were decreased. In contrast, seasonal allergic conjunctivitis was distinguished by an increase in Th17 and Th22 cell proportions, while the Th1 cell proportion decreased. Among tear fluid, the vast majority of pro-inflammatory cytokines (especially Th2 and Th17 cytokines) in perennial allergies and MMP-9 together with IgA in seasonal allergies were increased. In contrast, TGF-β2 was decreased in both forms of conjunctivitis. Finally, fungal (Malassezia species) and bacterial (Kocuria and Propionobacterium acnes species) colonization were observed in the perennial allergic conjunctivitis group. These results provide the basis for the development of a disease profile for perennial allergic conjunctivitis and open the door to new therapeutic and diagnostic strategies.

Role of the ocular surface microbiome in allergic eye diseases

“…Furthermore, the ratio of genera Bacillus/Acinetobacter (B/A) was higher in the OSM of AC patients, which may be a more specific biomarker for allergy-related inflammatory status [39 ▪ ]. There is also some preliminary evidence to suggest a subtle difference in conjunctival microbial profiles of PAC compared to SAC patients, with detection of Kocuria and Pseudomonas acnes species only in PAC specimens, insinuating a higher state of allergic development in perennial disease compared to seasonal ones [41 ▪ ].…”

Cytokines in Allergic Conjunctivitis: Unraveling Their Pathophysiological Roles

“…Conjunctival epithelial cells play a role in receiving and sending immune signals. Leukocytes are found scattered throughout the healthy conjunctival epithelium [ 32 , 33 , 34 ]. The most common cell types in the conjunctival epithelium are CD8 + T cells [ 33 ] and Langerhans cells [ 35 , 36 , 37 ].…”

Functions of mucosal associated invariant T cells in eye diseases

“…Allergic conjunctivitis is associated with chronic inflammation at the ocular surface where there is immunoregulatory interplay between commensal microbiota, conjunctival intraepithelial lymphocytes and epithelial cells ( 62 ). Approximately 16% of CD45 + leukocytes in the upper tarsal conjunctiva of healthy individuals were MAIT cells ( 63 ). MAIT cell frequency was not increased at the ocular surface in patients with chronic allergic conjunctivitis, in whom Cutibacterium acnes became the predominant commensal bacterial population ( 63 ) ( Figure 1 ).…”