Differences in systemic and skin migrating-specific CD4 T cells in papular urticaria by flea bite

Background: Papular urticaria by flea bite is a chronic allergic condition in which clinical improvement may occur at the age of 7 years, thus representing a natural model of acquired immunologic tolerance in humans. The aim of this study was to characterize regulatory cells and specific responses to flea antigens of CD4⁺ T lymphocytes expressing cutaneous migration markers in patients with papular urticaria caused by flea bite and with different disease evolution times. Methods: Cell populations were characterized by flow cytometry in samples from patients and healthy controls. Specific cell stimulation was performed with a complete flea body extract. The Mann-Whitney U test was used for comparisons. Results: Total dendritic cells were lower in patients than in healthy controls. No quantitative differences were found in CD4 regulatory T cells. CD4⁺ T cells from patients produced more IL-4, lL-10, IL-17, and IFN-γ. Patients who experienced the onset of symptoms within the first 5 years of age showed a greater percentage of local (cutaneous lymphocyte antigen +) IL-4- and IL-17-producing cells, while patients who experienced the onset of symptoms after the age of 5 years had a higher percentage of systemic (cutaneous lymphocyte antigen -) IL-10-producing cells. Conclusion: Analysis of the cellular immune response against whole flea antigen in patients with papular urticaria by flea bites suggests a possible participation of inflammatory cytokines in the skin reaction (Th17) and a systemic control mechanism (IL-10). This pattern of cytokine production in patients could be a consequence of an impaired dendritic cell population.