Allergic conjunctivitis and gut microbiota

Pubblicato il

Monday, 4 March 2024

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Ocular Inflammations

Allergic conjunctivitis has a major impact on the quality of life of all those who suffer from it. But what's new from genetic research.

Spring is approaching and, even in the altered rhythm of the seasons brought about by climate change, with the first fine days, the nightmare of spring allergies and, in particular, allergic conjunctivitis, appears on the horizon for sufferers.

Allergic conjunctivitis is an inflammatory, autoimmune-based eye disease that affects the conjunctiva, eyelids and cornea. Among the most frequent forms are seasonal allergic conjunctivitis (SAC) and the Perennial allergic conjunctivitis (CAP). The first, arising during spring and/or summer, is triggered by the presence of pollen in the air, usually of grasses. SAC is often also associated with significant symptoms affecting the nasal passages, and in this case we speak of rhino-conjunctivitis.

The Perennial allergic conjunctivitisOn the other hand, it can occur at all times of the year and for this allergic form, the allergens can be different: dust mites, pet dander or the presence of fungal spores, as well as mould.

In recent years, growing evidence has emerged of a decisive role played by the gut microbiota in balancing and modulating the immune response and in the pathogenesis of allergic manifestations. This finding implies that an imbalance in the gut microbiota could be a useful marker in predicting the onset of allergic conjunctivitis. In particular, from the perspective of predictive, preventive and personalised medicine, clarifying this role of gut microbiota imbalance in the onset of allergic conjunctivitis could offer an opportunity for primary prediction first and then for targeted prevention and, finally, for customised treatment of the disease.

In a study, published in May 2023 in the EPMA Journal, the official organ of Evidence-based Predictive, Preventive & Personalised Medicine, researchers tested the hypothesis that individuals with gut dysbiosis may be more susceptible to allergic conjunctivitis due to an increased inflammatory response. To this end, genetic variants related to gut microbiota conditions (N= 18,340) and allergic conjunctivitis (4,513 cases, with 649,376 controls) were selected from genome-wide association studies.

Innovative Screening and Targeted Interventions
With the advent of modern sequencing technologies targeting the 16S ribosomal RNA gene (16S rRNA), it is now possible to rapidly and cost-effectively analyse microbial communities in the gut from faecal samples, which can be obtained easily and non-invasively.

Identifying an alteration in the gut microbiota is crucial, not least because allergic conjunctivitis can serve as an early and reliable indicator of systemic disorders such as atopic dermatitis and asthma. Sequencing of the 16S rRNA gene showed that people who are at risk of a reduction in the Ruminococcaceae_UCG_002 , Holdemanella, Catenibacterium, Senegalimassilia and increased levels of the Oscillospira are at increased risk of allergic conjunctivitis.

Subjects identified in this way should undergo aggressive early treatment to correct the dysbiosis, such as: changing the diet, taking probiotic supplements and prebiotics.

Recent studies confirm that certain probiotic strains are able to alleviate the symptoms of allergic conjunctivitis. Probiotics are naturally occurring microorganisms that are compatible with those naturally present in the gut and make up, together with prebiotics, the intestinal ecosystem which, between harmless and pathogenic microorganisms, hosts more than 400 species.

For example, you can raise the level of Ruminococcaceae_UCG_002 with targeted probiotic supplementation, while targeted antibiotics can be administered to suppress the growth of Oscillospira.

Furthermore, 'high-throughput' 16S rDNA sequencing could become a routine test to identify alterations in the gut microbiota in patients with allergic conjunctivitis, which would be the first step to then delineate the specific probiotic strains for each patient, modify their diet and administer specific antibiotics to improve the inflammatory response and symptoms and improve the quality of life from the early stages of allergic conjunctivitis. This approach is also very useful for secondary prevention of the disease. Remember that primary prevention consists of preventing an individual from becoming allergic, while secondary prevention consists of preventing contact with the allergen.