The Ocular Surface and Immunity
Investigative Ophthalmology & Visual Science
The Human Microbiome Project characterized the microbiomes of various body sites, but the eye was not among them. Zysset-Burri et al. conducted a study to better understand the microbial composition of the ocular surface and its relationship to the tear proteome. They found a crucial immune-defense link between these systems.
For this study, the authors collected lid swabs, conjunctival swabs, and tear fluid from 20 patients (20 eyes). The mean age of participants was 69.7 years; 75% were male. Swabs were processed, and DNA was isolated and underwent whole-metagenome shotgun sequencing. The tear proteome was identified using chromatography in tandem with mass spectrometry. Linear modeling was applied to explore interactions between the microbial or functional features of the microbiome and the functional features of the tear proteome.
Altogether, 229 taxa were found in ocular surface microbiomes. The majority (93.15%) were bacteria, 6.83% were viruses, and 0.02% were eukaryotes. The ocular microbiome was dominated by the phyla Actinobacteria and Proteobacteria. The most abundant class was Actinobacteria (63.1%), and the most prevalent genera were Propionibacterium (31.9%), Agrobacterium (22.4%), and Corynebacterium (21.2%). P. acnes and Staphylococcus epidermidis were much more common in lid samples than conjunctiva (p = .015 and .020, respectively). Lid microbiomes were enriched in genes of stage 3 glycolysis as well as de novo adenosine and L-isoleucine biosynthesis pathways. More than 2,100 protein groups were identified from human tear proteome. The most prevalent proteins were lactotransferrin, albumin, lipocalin-1, lysozyme, and immunoglobulin A. All of these except albumin have antimicrobial activity. Gene ontology terms were assessed for correlation with tear and lid findings. Positive correlations were found for the Firmicutes phylum and the term fatty-acid binding; for the Agrobacterium genus and vitamin B1 synthesis and the term upregulated antimicrobial activity; and between the term sensory perception of chemical stimus and the biosynthesis of heme, L-arginine, and L-citrulline.
These findings highlight the integral interplay of the ocular surface microbiome and tear proteome in ocular health, said the authors. They believe this knowledge could lead to new strategies to prevent and treat diseases of the ocular surface.
The original article can be found here.