Dendritic cells in the dermal infiltrate of Sézary syndrome

Ordered array of dendritic cells and CD8+ lymphocytes in portal infiltrates in chronic hepatitis C

AIMS

Despite the importance of dendritic cells in stimulating primary and secondary immune responses by presenting antigens to T-lymphocytes in draining lymph nodes and peripheral tissues, respectively, very limited information is available on the presence and localization of these cells in hepatitis C virus (HCV)-related chronic active hepatitis. Therefore, we addressed the ultrastructure, immunophenotype, distribution and relationships to lymphatics of dendritic cells in portal infiltrates of this disease.

METHODS AND RESULTS

Part of percutaneous diagnostic liver biopsies (Knodell's histological assessment index: 9-13) was processed for electron microscopy and for immunohistochemical detection of immune system cell membrane antigens and of the lymphatic endothelium marker podoplanin. In portal infiltrates, cells with electron microscopical and cell marker features of dendritic cells and expressing the activation markers CD54, CD80, CD83 and CD86 were organized in a discontinuous network, that embedded CD8+ lymphocytes in close contact with dendritic cells and came in contact with hepatocytes, sometimes infiltrating beyond the limiting plate. Also, dendritic cells were found within newly formed lymphatic capillaries in thin, infiltrated septa among hepatocytes.

CONCLUSIONS

This evidence strongly suggests a critical role of dendritic cells and newly formed lymphatics in the pathogenesis and organization of the immune infiltrate that characterizes HCV-related chronic active hepatitis.

Interstitial dendritic cells of the rat heart. Quantitative and ultrastructural changes in experimental myocardial infarction

BACKGROUND

This study was undertaken to investigate the qualitative and quantitative changes that interstitial dendritic cells (IDC) of the heart undergo during the time course of experimental myocardial infarction.

METHODS AND RESULTS

Left coronary arterial ligations were performed in 43 rats that were killed 2, 4, 7, 14, and 21 days after surgery. Thirteen unoperated and 39 sham-operated rats were used as controls. Frozen sections were stained with monoclonal antibodies (OX 6 and W3/25) to identify and count IDC by light microscopy. Immunoelectron microscopy was also used to identify IDC. The number of IDC per mm2 of tissue section was calculated for all hearts. In hearts with myocardial infarction, IDC were counted in three areas: the center of the myocardial infarction, the border zone, and the noninfarcted left ventricle. In OX 6 antibody-stained preparations, the number of IDC per mm2 was 82 +/- 10 in the left ventricle of unoperated rats. Hearts with myocardial infarction showed marked increases in the numbers of IDC per mm2 in the border zone (796 +/- 79 at 7 days and 528 +/- 98 at 14 days). In the border zone, IDC often were associated with small clusters of T-helper lymphocytes, which reacted with W3/25 antibody (the rat homologue of human CD4). The center of the myocardial infarction showed an increase in IDC only on day 7 (120 +/- 18). By 21 days, IDC in the border zone were only slightly increased (159 +/- 15).

CONCLUSIONS

These findings suggest that IDC migrate to the myocardial infarction border zone. They participate in the activation of lymphocytes and in the initiation of immune responses and decrease in number as inflammation subsides and scarring develops.

Morphology and membrane antigens of nonlymphoid accessory cells in oral hairy leukoplakia

We have investigated the features and distribution of accessory cells (ACs) and the relationship of these cells to each other and to lymphocytes in the epithelium and lamina propria of oral hairy leukoplakia (HL), with the objective of better defining the differentiation and mutual interactions of immune-response cells within HL as a preliminary step to understanding the onset and significance of this lesion during human immunodeficiency virus (HIV) infection. Twenty-four HIV-infected patients with HL, two asymptomatic HIV-positive subjects, and three HIV-negative subjects were studied by immunohistochemistry; five HIV-positive patients with HL and three asymptomatic HIV-positive subjects were studied by electron microscopy. In both the epithelium and the lamina propria of HL, we found cells with the immunohistochemical and ultrastructural features of variably differentiated ACs; differences were found between the epithelium and lamina propria. In the lamina propria, ACs were characterized by dendritic shape, multiple contacts with lymphocytes, expression of CD1a antigen, and ultrastructural features of fully differentiated ACs. Conversely, in the epithelium ACs showed bluntly dendritic shape, low expression of CD1a, absent expression of HLA-DR, constant expression of CD11c and CD14 antigens, only occasional contacts with lymphocytes, and ultrastructural features of variably, but always incompletely, differentiated cells of monocyte-dendritic lineage. Seventy-nanometer wide intracisternal particles, closely resembling A particles described in retroviral infections, were found in the intraepithelial ACs in two patients with HL. The defective differentiation of ACs in the epithelium of HL--possibly influenced by the perturbation of the epithelial microenvironment induced by Epstein-Barr virus, and following the direct HIV infection of these cells--and the exceptional finding of close contacts with lymphocytes suggest that the lesional epithelium of HL may constitute a pathway for the entry of foreign antigens which circumvent monitoring by ACs and can induce immune tolerance. The impairment of the local immune response in HL may contribute to the development of full blown, systemic immunodeficiency.

Langerhans cells and mycosis fungoides--a critical overview of their pathogenic role in the disease

Skin biopsies from seven patients with mycosis fungoides in various clinical stages (patches, plaques, nodules) were studied immunohistochemically and ultrastructurally, with the aim of investigating and quantifying the distribution of Langerhans cells and their relationships to mycosis cells. Our findings have revealed that in patches and plaques both Langerhans cells and mycosis cells were numerous in the epidermis. Notwithstanding this, in all the specimens examined, only one Langerhans cell forming close contact with a mycosis cell was detected. In the nodules, Langerhans cells and mycosis cells were sparse in the epidermis and no contacts were seen between them. Moreover, in all the patients studied, only a single Langerhans cell was found in the dermal infiltrate without any closely related mycosis cells. Conversely, numerous interdigitating cells have been found in the dermis of patches and plaques, often tightly adhering to mycosis cells. In the nodule, a few scattered interdigitating cells were seen, but often these had close contacts with neoplastic lymphoid cells. These findings indicate that close apposition between Langerhans cells and mycosis cells, which led previous authors to hypothesize a persistent stimulatory action of Langerhans cells on T lymphocytes, eventually leading to the malignant transformation of the latter, is unusual in mycosis fungoides. Therefore, if such a pathogenic role may be attributed to accessory cells in mycosis fungoides it is more probably exerted by dermal interdigitating cells and not by Langerhans cells, as previously proposed.

Interdigitating reticulum cells in lymph nodes of Sézary syndrome. Freeze-fracture and ultrathin-section morphology

Lymph nodes with extensive leukemic infiltration from three patients with the Sézary syndrome were examined in ultrathin sections and in freeze-fracture replicas. Sézary cells (SC) and interdigitating reticulum cells (IDC) were the predominant cell types in the lymph nodes. Both were closely connected with each other by apparently interdigitating cytoplasmic processes. The projections between these cells were, in the main, processes from the IDC. In freeze-fracture replicas these cellular processes did not appear as interdigitations but were more bubble-like, and for this reason these cells are imprecisely described by the term "interdigitating." The SC were seen to possess only short cytoplasmic processes. The frequent polar grouping of cell organelles in SC in the region of the contact zone with IDC and the high organelle content of IDC ('activated IDC') could be the morphologic expression of intense interaction between IDC and SC. IDC displayed three features in freeze-fracture which are not specific to the Sézary syndrome, but should be applicable to IDC in general: (1) they exhibited an approximately equal density of intramembrane particles in both the E-face and the P-face, (2) some of the intramembrane particles in the P-face were assembled in clusters and (3) the surface showed bubble-like formations of the cytoplasmic processes. On the basis of these properties it was possible to distinguish IDC from macrophages and lymphocytes in freeze-fracture replicas.

Immunohistochemical study of epidermal Langerhans cells and dermal dendritic cells in benign and malignant skin lesions characterized by a dermal lymphoid infiltrate consisting either of B-cells or T-cells

Skin biopsies from 43 patients with a rather dense dermal lymphoid infiltrate of either inflammatory or neoplastic nature have been investigated. We studied the number, distribution and immunophenotype of epidermal Langerhans cells and dermal dendritic cells. As previously reported, differences in epidermal Langerhans cell and dermal dendritic cell numbers between skin biopsies with a B-cell infiltrate and skin biopsies with a T-cell infiltrate were found, dendritic cells being more numerous in the latter. The main finding of this study was an uneven distribution of epidermal Langerhans cells and dermal dendritic cells in skin biopsies with a T-cell infiltrate: in skin lesions with an inflammatory lymphoid infiltrate, small clusters of epidermal and dermal dendritic cells admixed with T-lymphocytes (predominantly T-helper/inducer cells) and small blood vessels were present at areas of exocytosis. In skin lesions with a neoplastic lymphoid infiltrate larger, more loosely arranged aggregates of dendritic cells and T-cells were seen. These cell aggregations composed of activated (inflammatory or neoplastic) T-cells and dendritic cells may represent the cutaneous homologue of the secondary T-nodule in the lymph node. Both types of cell aggregates may correspond to the dendritic cell-T cell clusters observed in in vitro induced immune responses.