The immune response in halo nevi.

The mechanism(s) responsible for halo nevus presents a provocative link with the immune response to melanoma. Although no direct demonstration of melanocyte killing has been observed by the immune effector cells found within the halo, the abundance of antigen-presenting cells in the regressing nevus and the presence of T lymphocytes at the site of depigmentation suggest that these cells participate in the halo phenomenon. Within the latter population of cells, evidence points to the involvement of CD8+ T cells as potential effectors in the destruction of nevomelanocytes. The break in tolerance that triggers migration and the presumed activation of these and other lymphocytes in the nevus in the apparent absence of disease remains unexplained. This brief overview reviews the evidence for the participation of the immune response in the genesis of the halo nevus.