This study aims to evaluate the effector function and expression of TIGIT and PD-1 on Tregs, as well as the Th2/Treg ratio, in patients with allergic conjunctivitis with and without desensitization therapy, compared to healthy controls.

Peripheral blood and tear samples will be collected once at enrollment. Treg and Th2 populations will be immunophenotyped, TIGIT and PD-1 expression assessed, and functional assays performed. Cytokine and antibody (IgE, IgG4) concentrations will be measured in serum and tears.

Results will be analyzed using descriptive statistics, Shapiro-Wilk test for distribution, t-tests or ANOVA for group comparisons, and correlation analyses for associations, with p<0.05 considered significant. This study seeks to identify immunological markers associated with disease severity and treatment response, potentially informing future therapeutic strategies.

Allergic conjunctivitis is a prevalent ocular condition affecting approximately 10-20% of the global population, with 40-60% of allergic individuals exhibiting ocular symptoms. It is characterized by redness, itching, burning, and tearing, which result from excessive activation of immune response cells. Severe forms can significantly impact vision and quality of life, particularly in children, adolescents, and young adults. The disease is mediated by hypersensitivity reactions: Th2 lymphocytes release cytokines (IL-4, IL-5, IL-13) that stimulate IgE production by B lymphocytes. IgE binds to mast cells and induces the release of pro-inflammatory mediators upon allergen recognition. Regulatory T cells (Tregs) play a critical role in maintaining immune homeostasis by suppressing the activation and proliferation of effector T cell subsets, including Th1, Th2, Th9, and Th17, via cell-surface molecules such as TIGIT, LAP-TGF-β, and PD-1. Additionally, Tregs produce IL-10, which suppresses IgE production and induces IgG4 secretion by B cells. Allergen-specific immunotherapy (desensitization) has been employed to reduce symptoms and prevent recurrence in allergic diseases.

Rationale:

Allergic conjunctivitis is a public health concern that affects the quality of life of a substantial portion of the Mexican population. Immunological imbalances between effector T cells and Tregs have been reported. Understanding the balance of these subpopulations and the role of TIGIT and PD-1 molecules in Treg functional status is critical to elucidating disease mechanisms. Moreover, it is important to determine whether desensitization therapy induces changes in the Th2/Treg ratio and modulates TIGIT and PD-1 expression, which could serve as biomarkers of treatment response or therapeutic targets.

Hypothesis:

The effector function and expression of TIGIT and PD-1 on Tregs are decreased in patients with allergic conjunctivitis and are enhanced following desensitization therapy.

Objectives:

The primary objective is to evaluate the effector function and expression of TIGIT and PD-1 on Tregs and the Th2/Treg ratio in patients with allergic conjunctivitis with and without desensitization therapy, compared to healthy controls. Secondary objectives include assessing correlations between immunological parameters and clinical severity of ocular symptoms and response to treatment.

Study Design and Methods:

This observational, cross-sectional, case-control study will include patients with allergic conjunctivitis, with or without desensitization therapy, and healthy control subjects. Peripheral blood and tear samples will be collected once at enrollment. Peripheral blood mononuclear cells will undergo immunophenotyping to quantify Treg and Th2 populations and assess TIGIT and PD-1 expression. Tregs will be isolated for functional assays. Cytokine concentrations associated with Th2 and Treg cells, as well as IgE and IgG4 levels, will be measured in serum and tears.

Statistical Analysis:

Descriptive statistics will summarize participant characteristics and study outcomes. The Shapiro-Wilk test will assess data distribution. Comparisons between two groups will use t-tests (parametric or non-parametric), and comparisons among more than two groups will use ANOVA (parametric or non-parametric). Correlation analyses will evaluate associations between immunological parameters and clinical outcomes. A p-value <0.05 will be considered statistically significant.

Inclusion Criteria:

• Subjects aged between 5 and 30 years, of either sex.
• Subjects with a confirmed diagnosis of allergic conjunctivitis.
• Presence of active symptoms.
• Positive skin tests.
• Willingness to participate in the protocol by signing informed consent.

Exclusion Criteria:

• Subjects who have had an infection within the two months prior to sample collection.
• Patients with other active systemic allergic diseases (such as bronchial asthma, dermatitis, among others).
• Subjects with chronic-degenerative or autoimmune diseases.
• Subjects who have received topical immunosuppressive treatment in the last two months.
• Subjects receiving systemic immunosuppressive therapy.

The study subjects are patients recruited from the outpatient clinic of "Clinical Immunology" at Instituto de Oftalmologia Conde de Valenciana. All patients are evaluated by specialists in ophthalmology and allergy.