CHARACTERIZATION OF THE MONONUCLEAR INFILTRATE INVOLVED IN REGRESSIONOF HALO NEVI

Halo nevi are characterized by progressive degeneration of nevus cells surrounded by a mononuclear cell infiltrate. We studied the morpholog ical features of the nevus cells and the composition of the mononuclea r cell infiltrate in 15 cases of halo nevi using immunohistochemical t echniques and a battery of antibodies to different subsets of lymphocy tes and histiocytes. Regression could be divided into four more or les s identifiable stages, associated with different subsets of lymphocyte s and monocyte-macrophage lineage cells. Stage I (pregression): nests of unremarkable nevus cells were surrounded by a moderate number of T lymphocytes (relatively small percentage of helper/inducer T cells), o ccasional B cells and macrophages. Stage II (early regression): large number of T lymphocytes and FXIIIa-positive cells were in dose contact with nevus cell clusters which showed ragged edges. Lysozyme-positive cells and epidermal Langerhans cells were mildly increased. Stage III (late regression): single nevomelanocytes showing mild atypia were pr esent. Numerous T lymphocytes and macrophages positive for lysozyme, K P1 and/or FXIIIa were interspersed between the nevus cells. Increased numbers of epidermal Langerhans cells were present. Stage IV (complete regression): no nevus cells were observed and moderate numbers of T l ymphocytes only remained. These results suggest that T cells, especial ly T-suppressor cells, and different subsets of macrophages participat e in the regression of the nevi. (C) Munksgaard 1994.