Background: There have been few clinical studies of the role of regulatory T cells (Tregs) in halo formation of halo nevus. Objective: To evaluate the clinicopathologic features and the presence of Tregs in halo nevi. Methods: We analyzed 30 halo nevi and performed immunohistochemical analysis using antibodies against CD4, CD8, CD25 and Foxp3. We also performed double immunohistochemical staining for Foxp3 and CD25. Results: We found significant increases in Foxp3⁺ Tregs, and the shorter the halo nevus duration, the more Foxp3⁺ Tregs were detected. Also, the ratio of Foxp3 to CD8 T cells was increased in early stages of halo nevi. Double immunohistochemical staining suggested that the Tregs in the halo nevi were CD25⁺Foxp3⁺ T cells. Conclusions: Foxp3⁺ Tregs were greatly increased in the halo nevi. The shorter the halo nevi duration, the more Foxp3⁺ Tregs were involved in the earlier developmental stages of halo nevi.

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