Pathomechanisms of photosensitive lupus erythematosus.

This review discusses the mechanisms involved in different photosensitive lupus syndromes: acute cutaneous lupus erythematosus, chronic cutaneous (discoid) lupus erythematosus, subacute cutaneous lupus erythematosus, and neonatal lupus erythematosus. It is proposed that there are three principal determinants of photosensitivity in lupus: 1) susceptibility to UVR-induced release of epidermal and dermal cytokines; 2) susceptibility to UVR-induced release or translocation of sequestered antigens in the epidermis or dermis; and 3) different specific immunologic effector mechanisms, activated by cytokines and directed against discrete epidermal targets. Several characteristics of photosensitive lupus are discussed in detail: autoantibody specificities, autoantigen translocation, induction of epidermal intercellular adhesion molecule-a (ICAM-1), vascular activation, cytokine release and T-cell activation, and clinical phototesting. The role of antibodies to the extractable nuclear antigens Ro and La and the relationship to subacute cutaneous lupus erythematosus (SCLE) and neonatal lupus erythematosus is discussed in detail, and a model of SCLE is proposed.