The reports of induced pemphigus have multiplied over the last 10 years. Several heterogeneous factors, such as drugs (penicillamine, pyritinol, captopril, rifampicin, etc.), physical agents (burns, UV, and ionizing radiation) and viruses, can play an inducing role. Usually, the disease is preceded by prodromal, non-specific lesions. The full-blown stage shows features of pemphigus foliaceus, erythematosus or herpetiformis. Histologically, acantholytic splits mostly occur at the highest malpighian layers. Intercellular antibodies and frequently concomitant other auto-antibodies are found in the serum, the titre of the former usually being low and unrelated to the severity or course of the disease. The biological progress is variable and ranges from rapidly and definitively healing cases (induced pemphigus proper) to others which, in spite of the elimination of the inducing factor, self perpetuate just like true pemphigus (triggered pemphigus). Pathogenic hypotheses are based on the act that some inducing factors can alter the antigen distribution on keratinocyte membranes and/or interfere with immune surveillance by impairing T-suppressor cells.

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The possible acantholytic property of captopril and thiopronine has been investigated using in vitro tissue cultures. Normal human breast skin explants have been cultured in Hanks’ balanced salt solution containing 40% normal inactivated human serum with the addition of L-cysteine, or reduced glutathione (GSH), or captopril, or thiopronine, at four different concentrations (1, 5, 10, 15 mM). Patterns of diffuse, mainly suprabasal acantholysis, with formation of bullae, were observed in the skin explants cultured with captopril or thiopronine at a 15-mM concentration after 5 days of culture; intraepidermal splits were present also at a 10-mM concentration. Focal acantholysis was seen in specimens cultured with L-cysteine or GSH at a 15-mM concentration. No lesions occurred in the samples treated with lower concentrations of the above substances, nor in controls. The results show a biochemical acantholytic potential of both captopril and thiopronine, resembling that of penicillamine in similar experimental conditions, and consonant with clinical observations of pemphigus induced by drugs containing thiol groups in their molecule (SH drugs).

Kaposi's sarcoma appeared on a chronically lymphedematous leg of a 75-year-old man. Immunologic investigations revealed a lack of cellular immune response confined to the involved lower limb. Regional disorders of immune surveillance are thought to play an important role in the early stages of Kaposi's sarcoma.

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