Decreased density of epidermal dendritic cells in melanocytic naevi: the possible role of in vivo sun exposure.

Melanocytic naevi are benign skin tumours that originate in the epidermis. The pathogenesis of naevi and cutaneous malignant melanoma has been linked to sun exposure. This study evaluates alterations in the density of immunologically active epidermal dendritic cells (EDCs) in naevi in response to sun exposure. Immunohistologically stained sections of 266 naevi from patients from Israel (n = 135) and Germany (n = 131) were evaluated. The proportion of naevi with decreased density of HLA-DR+ (dDR+) and CD1(a)+ (dCD1(a)+) EDCs was analysed according to country, last exposure to sunlight, anatomical location and histological subtype. The risk of dDR+ was found to be linked to residence in Israel compared with Germany (odds ratio [OR] = 4.2; 95% confidence interval [CI] = 2.0-8.9), suggesting a latitude-dependent effect. Naevi removed in summer had a higher risk of dCD1(a)+ (OR = 4.7; 95% CI = 2.3-9.8) compared with those removed in winter. The most conspicuous dDR+ among the German cases, and dCD1(a)+ among the Israelis, occurred in naevi located on commonly exposed skin. The similar densities of EDCs in the lesional and perilesional skin of the majority of the naevi indicates that the underlying naevus cells have no effect on EDC density. It is not unlikely that an altered immune response due to dDR+ and dCD1(a)+ in sun-exposed skin in the vicinity of naevi contributes to the subsequent melanoma risk in highly susceptible individuals. (C) 1999 Lippincott Williams & Wilkins.