The involution of the central pigmented lesion in halo nevus (HN) seems to be mediated by an immune response against self antigens expressed by melanocytes.

We assessed the presence of activated lymphocytes in the peripheral blood lymphocytes from patients with HN.

Peripheral blood was obtained from patients with HN associated with benign pigmented lesions (5) or melanoma (2) as well as from patients with melanoma without HN (5) and healthy subjects (10). Activated lymphocytes were detected by flow cytometry analysis using monoclonal antibodies (mAb) against CD69, CD71, CD98, HLA-DR, and activated β₁ integrins (HUTS-21 mAb).

The peripheral blood lymphocytes from patients with HN, associated with either benign or malignant lesions, exhibited a significantly higher expression of all activation markers studied compared with patients with melanoma without HN or compared with healthy subjects. Therefore the peripheral blood of HN patients contained a significant fraction of lymphocytes with an activated (CD69⁺, HLA-DR⁺, CD98^bright), cell proliferating (CD71^bright), and high adhesive (HUTS-21^bright) phenotype. These activated cells disappeared from peripheral blood after the surgical resection of the skin lesion.

Our findings further support the involvement of immune activation in HN phenomenon.