Faculty Bibliography

Although Sezary syndrome (SS) represents an advanced stage of cutaneous T-cell lymphoma, this diagnosis presents a challenge even for the most experienced dermatologic clinicians. SS is characterized clinically by erythroderma, but can also be identified in the presence of specific histologic and peripheral blood findings. Erythrodermic cutaneous T-cell lymphoma can mimic a number of nonmalignant disorders with erythroderma, including pityriasis rubra pilaris, psoriasis, atopic dermatitis, and graft-versus-host disease. The diagnosis is made even more challenging because the histology of SS is often nonspecific and rarely pathognomonic. As a result, peripheral blood studies in patients with erythroderma are frequently informative in the diagnosis of SS. Peripheral blood abnormalities including elevated CD4/CD8 ratio, aberrant CD26, CD27 and CD7 expression, and T-cell clonality can all be used to help arrive at a diagnosis. This review evaluates current data on the usefulness and limitations of specific peripheral blood markers detected by flow cytometry and T-cell receptor gene rearrangement polymerase chain reaction.

Pemphigus vulgaris is a blistering disease associated with autoantibodies to the desmosomal adhesion protein, desmoglein 3. Genetic deficiency of desmoglein 3 in mice mimics autoimmunity to desmoglein 3 in pemphigus vulgaris, with mucosal-dominant blistering in the suprabasal layer of the epidermis. Mice with an epidermal-specific deletion of desmocollin 3, the other major desmosomal cadherin isoform expressed in the basal epidermis, develop suprabasal blisters in skin that are histologically identical to those observed in pemphigus vulgaris, suggesting that desmocollin 3 might be a target of autoantibodies in some pemphigus vulgaris patients. We now demonstrate that desmocollin 3 is an autoantigen in pemphigus vulgaris, illustrated in a patient with mucosal-dominant blistering. Six of 38 pemphigus vulgaris and one of 85 normal serum samples immunoprecipitate desmocollin 3 (P = 0.003). Incubation of patient IgG with human keratinocytes causes loss of intercellular adhesion, and adsorption with recombinant desmocollin 3 specifically prevents this pathogenic effect. Additionally, anti-desmocollin 3 sera cause loss of keratinocyte cell surface desmocollin 3, but not desmoglein 3 by immunofluorescence, indicating distinct cellular pathogenic effects in anti-desmocollin and anti-desmoglein pemphigus, despite their identical clinical presentations. These data demonstrate that desmocollin 3 is a pathogenic autoantigen in pemphigus vulgaris and suggest that pemphigus vulgaris is a histological reaction pattern that may result from autoimmunity to desmoglein 3, desmocollin 3, or both desmosomal cadherins.