La cellule de Langerhans : cellule dendritique de l'épiderme et des muqueuses

Human thymic dendritic cells

ABSTRACT Human thymic dendritic cells (DC) represent a member of the bone marrow-derived dendritic cell family. They have a dendritic shape and are found in small numbers mainly at the corticomedullary border and in medullary regions of the thymus. Human thymic DC were isolated by density gradient separation, followed by treatment with CD2, CD7, CD1, and CD11b mAb and immunobeads magnetic separation. The resulting population contains 60-75% brightly HLA-DR+ cells which present the morphological characteristics of DC observed in situ. Extensive phenotypic analysis confirmed that they are of mesenchymal origin and that some express CD11a and CD54 molecules. Freshly isolated DC do not stain with a wide variety of anti-T-B and -monocyte or -macrophage mAb. However, they acquire the CD1 molecule after a few days in culture. By using a cell sorter we obtained 90-95% of purified human thymic DC. Functional studies have shown that human thymic DC are potent activators in mixed lymphocyte reactions, act as accessory cells in mitogenic thymocyte proliferation, increase the thymocyte proliferative response to a toxin signal, and produce IL-1. They also formed spontaneous physical associations with thymocytes, which raises questions about the implication of DC in differentiation and/or maturation processes of thymocytes.

Quantitative analysis of the immune cells in the anal mucosa

The prevalence of anoperineal diseases, i.e. sexual transmitted infections, is increasing particularly in AIDS, a fact which is likely due to the alteration of mucosal immunity. However, no data were available on normal anal status. In order to study anal immunity in man, we characterized lymphocytes subtypes and Langerhans' cells (LC) using quantitative morphometric analysis and immunohistochemistry. Anal normal mucosal samples obtained from surgical specimens of 45 patients (30 suffering from hemorrhoids and 15 from fissurations) were analyzed. Immunohistochemistry was performed on frozen sections with antibodies recognizing CD1a (LC), CD3 (T lymphocytes), CD4 (T4), CD8 (T8) and CD22 (B-lymphocytes). Immunostained cells were counted per square millimeter of mucosal epithelium. The surface of CD1a cells was measured using a computerized software program and a percentage of CD1a immunostained area was calculated in comparison to the whole mucosal surface. LC and T-Lymphocytes were found in the squamous epithelium in all analyzed samples. The mean values of LC number were 84.13 +/- 9.6 and 64.77 +/- 9.8 in hemorroid- and fissure-patients, respectively. The mean values of LC area (% of CD1a stained area over total mucosal surface) were 3.89 +/- 0.44 and 4.84 +/- 0.64, respectively. In the two groups, the number of intraepithelial CD8 lymphocytes was higher than that of CD4 lymphocytes. These data suggest for the first time that anal mucosa could be considered as a part of MALT system.

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

Langerhans cells are dendritic cells of the epidermis originating from bone marrow precursors which may exceptionally undergo mitosis within the skin. We report herein an electron-microscopic observation of a dividing LC within a seemingly hyperproliferative human epidermis. This observation further underlines the self-reproducing capacity of LC in situ and suggests that LC may respond to the same mitogenic stimuli as keratinocytes.