Exploring CD4 +CD8 + double-positive T cells in canine allergy and health: A pilot study.

Background
CD4 +CD8 + double-positive (DP) T cells are present in low numbers in the peripheral blood of both healthy and sick humans and dogs. In humans, these cells play cytotoxic or suppressive roles depending on the disease, but their function in dogs remains unclear.Objectives
This study aims to investigate the presence of DP T cells in a cohort of dogs with adverse food reactions (AFR), compare their frequency among AFR, non-food-induced atopic dermatitis (NFICAD), and healthy dogs (HTY), and evaluate whether DP T cells could serve as a diagnostic tool to differentiate between AFR and NFICAD and identify the culprit allergens in AFR dogs.Methods
Peripheral blood samples were collected from dogs with AFR, NFICAD, and healthy controls. PBMCs were isolated and analyzed by flow cytometry to assess T cell subpopulations. AFR dogs were grouped by their specific culprit allergens, and DP T cell proliferation in response to each allergen was compared across groups. An overall comparison of DP T cell proliferation was made between the three groups (AFR, NFICAD, HTY) under both stimulated and non-stimulated conditions. The mean percentage of proliferating DP T cells in healthy dogs was used as a cut-off to correlate with oral food challenge (OFC) results.Results
DP T cells proliferated in all groups, with the greatest proliferation observed in the AFR group when stimulated with food allergens. Statistically significant differences were found between AFR and NFICAD groups, with AFR dogs showing more proliferation. The test identified the culprit allergens in 28.57 % of cases, with false positives occurring in 17.86 %.Conclusions
DP T cells showed greater proliferation in food-allergic dogs compared to those with other allergic conditions like NFICAD. Despite these differences, overlapping results indicate that DP T cells are not a reliable screening test for distinguishing allergic from healthy dogs. While the test holds potential for identifying allergic phenotypes, it lacks sufficient diagnostic value for pinpointing specific allergens. Future studies with larger sample sizes and refined methods are needed to improve diagnostic accuracy.