Electron-microscopic observation of a human epidermal Langerhans cell in mitosis

Self-renewal capacity of human epidermal Langerhans cells: observations made on a composite tissue allograft

Epidermal Langerhans cells (LC) are dendritic, antigen-presenting cells residing within mammalian epidermis and mucosal epithelia. When massively depleted, they are replaced by cells of bone-marrow origin. However, their renewal within normal skin under steady-state conditions is not precisely known. We observed that epidermal LC within a human hand allograft remain stable in the long term (10 years) and are not replaced by cells of recipient's origin; furthermore, we observed a Langerhans cell in mitosis within the epidermis 8 years postgraft. These results show that under almost physiological conditions, human LC renew in the epidermis by local mitoses of preexisting cells.

CD1a expression in psoriatic skin following treatment with propylthiouracil, an antithyroid thioureylene

BACKGROUND

The antithyroid thioureylenes, propylthiouracil (PTU) and methimazole (MMI), are effective in the treatment of patients with plaque psoriasis. The mechanism of action of the drugs in psoriasis is unknown. Since the drugs reduce circulating IL-12 levels in patients with Graves' hyperthyroidism, the effect of propylthiouracil on CD1a expression in psoriatic lesions was examined in biopsy samples of patients with plaque psoriasis. CD1a is a marker of differentiated skin antigen presenting cells (APC, Langerhans cells). Langerhans cells and skin monocyte/macrophages are the source of IL-12, a key cytokine involved in the events that lead to formation of the psoriatic plaque.

METHODS

Biopsy specimens were obtained from six patients with plaque psoriasis who were treated with 300 mg propylthiouracil (PTU) daily for three months. Clinical response to PTU as assessed by PASI scores, histological changes after treatment, and CD1a expression in lesional skin before and after treatment were studied.

RESULTS

Despite significant improvement in clinical and histological parameters the expression of CD1a staining cells in the epidermis did not decline with propylthiouracil treatment.

CONCLUSIONS

It appears that the beneficial effect of propylthiouracil in psoriasis is mediated by mechanisms other than by depletion of skin antigen-presenting cells.

Langerhans cell microgranulomas (pseudo-pautrier abscesses): morphologic diversity, diagnostic implications and pathogenetic mechanisms

The term 'Langerhans cell microgranuloma' (LCM) was introduced a decade ago to draw attention to focal collections of these cells within the epidermal layer that develops during certain immune reactions. In spite of a growing awareness of this phenomenon during the past decade, few reports have focused on the development and phenotype of LCM. In this commentary, we review the historical development of the concept of LCM, demonstrate the salient immunomorphologic characteristics of LCM, and advance a hypothesis to explain their sequential evolution and formation.

Olmsted syndrome: report of two new cases and literature review

Olmsted syndrome is a rare keratinization disorder; 18 cases have been published so far. It associates a mutilating cogenital palmoplantar keratoderma with periorificial erythematokeratotic lesions. We report herein two new unrelated male children with Olmsted syndrome (OS), one of whom was studied by light and electron microscopy. Our histological, immunohistochemical, and ultrastructural findings suggest that this disease is related to epidermal hyperproliferation. We present herein a review of the twenty cases published so far and discuss the major clinicopathological and genetic features of this disease.