Electron microscopic identification of Langerhans cells in the dermal infiltrates of mycosis fungoides

Interaction of cutaneous lymphoma cells with reactive T cells and dendritic cells: implications for dendritic cell-based immunotherapy

BACKGROUND

Cutaneous T-cell lymphomas (CTCLs) are a heterogeneous group of skin neoplasms that originate from T lymphocytes. An anti-CTCL T-cell immunity has been described but seems to be inefficient to clear CTCL cells. It is not known whether cutaneous dendritic cells (DCs) perpetuate the proliferation of the malignant CTCL cell clone or play a role in the control of this usually slowly progressing disease.

OBJECTIVES

To characterize CTCL cell properties in the control of anti-CTCL T cells and to pave the way for a DC-based immunotherapy for CTCL.

METHODS

We studied the interaction of a CTCL cell line with DCs and with allogeneic T cells.

RESULTS

We found an antigen non-specific capacity of viable but not apoptotic CTCL cells to hamper CD4+ and CD8+ T-cell proliferation in a dose-dependent manner, indicating a suppressive potential of CTCL cells. Both viable and apoptotic CTCL cells were phagocytosed by immature DCs but only apoptotic CTCL cells induced an upregulation of DC maturation markers to a degree which enabled classification of these DCs as semimature. CTCL cells did not respond with proliferation when encountering allogeneic, mature DCs either loaded with CTCL cell material or unloaded, indicating a role for DCs in the induction of anti-CTCL T-cell immunity rather than in perturbation of clonal proliferation. For the loading of DCs with CTCL material lysate seems to be optimal as apoptotic cells were not phagocytosed extensively and necrotic CTCL material induced a partial cellular toxicity in DCs. DCs loaded with CTCL material were cryopreservable without significant loss of DC viability, surface marker expression or allostimulatory activity.

CONCLUSIONS

Together, these data argue in favour for a DC-based immunotherapy for CTCL patients and provide an experimental protocol for preparing CTCL cell-loaded DCs.

Density of neoplastic lymphoid infiltrate, CD8+ T cells, and CD1a+ dendritic cells in mycosis fungoides

BACKGROUND/AIMS

CD8+ T cells and epidermal/dermal dendritic cells expressing CD1a are found among neoplastic CD4+ T cells in mycosis fungoides (MF) lesions. This study analysed the relation of CD8+ tumour infiltrating lymphocytes (TILs), CD1a+ epidermal Langerhan's cells (LCs), and dermal dendritic cells (DDCs) to clinicopathological parameters in 46 MF cases.

METHODS

Pretreatment diagnostic biopsy specimens of 46 MF cases were submitted to histological analysis and immunohistochemistry. Four histological grades were defined based on the density of the neoplastic infiltrate: grade 1 (mild superficial perivascular infiltrate), grade 2 (moderate superficial perivascular infiltrate with some tendency to confluence), grade 3 (pronounced superficial band-like infiltrate), and grade 4 (deep nodular infiltrate). Epidermotropism was scored as low, moderate, or high. Numbers of CD8+ T cells and of dermal and epidermal CD1a+ cells were scored as 1 (low), 2 (moderate), and 3 (high). Correlations between these parameters and clinical data (age, sex, clinical type of lesions, stage, response to treatment, and recurrence) were analysed by the chi(2) test.

RESULTS

Numbers of TILs and DDCs were associated with subepidermal infiltrates, being lower in less dense infiltrates, whereas there was no association between epidermal CD1a+ cells and the analysed parameters. Complete remission in treated patients was related to subepidermal infiltrates but not to TILs, LCs, or DDCs.

CONCLUSIONS

These results support the notion that CD8+ cells and dermal CD1a+ cells are active against tumour cells. MF with low numbers of TILs could represent an early stage of the disease, before TILs are activated against tumour specific antigens.

Immunohistochemistry and electron microscopy in Langerhans cell histiocytosis confined to the skin

Four cases of benign Langerhans cell histiocytosis limited to the skin were studied. In all three self-healing cases (cases 2, 3, and 4) many dense bodies, myelin bodies, and worm bodies were found. In one chronic case (case 1) none of these was identified. In all four cases, in addition to CD1, HLA-DR, and S-100 stains, interferon-gamma and S-100 beta-subunit were positive in the dermal tumor cells. Both interferon-gamma and S-100 beta-subunits were negative in the normal epidermal Langerhans cells. A comprehensive literature review yielded 87 cases of skin-limited Langerhans cell histiocytosis. These cases could be subgrouped into three categories: (1) those that resolved spontaneously, (2) those that responded to therapy and had no recurrence, and (3) those with persistent or recurrent lesions, not responding to therapy but still limited to the skin.

A subpopulation of Langerhans cells (CD1a+Lag-) increased in the dermis of plaque lesions of mycosis fungoides

The population of CD1a+ cells and the quantity of Birbeck granules were evaluated in comparison with the population of T lymphocytes in a variety of clinical lesions of mycosis fungoides. Anti-CD1a and Lag antibodies that specifically react with Birbeck granules and related structures of human Langerhans cells were used immunohistochemically. CD1a+ cells in the dermis of lesions of mycosis fungoides significantly increased in plaques of the plaque stage and in plaques of the tumor stage. They were most frequent in lesions with CD4+ cells ranging in number from 100 to 150/mm2. These lesions were suspected to be progressing from the plaque to the tumor stage. During the course of the disease, most of the dermal CD1a+ cells had few Lag antigens. These results suggest that dermal CD1a+Lag- cells may promote the progression of mycosis fungoides from the plaque to the tumor stage.

Epidermal Langerhans' cell densities influence survival in mycosis fungoides and Sézary syndrome

Because Langerhans' cells (LC) (CD1a-positive epidermal cells) have been discussed to be involved in the pathogenesis of mycosis fungoides and Sézary syndrome, the authors examined the influence of densities of Langerhans' cells and, concurrently, of other phenotypes retrospectively on survival of 35 patients. Cell densities were assessed on cryostat sections (alkaline phosphatase antialkaline phosphatase-technique) of the respective diagnostic biopsy specimens. Additionally, two clinical parameters (age, stage of disease) were evaluated. CD1a-positive epidermal cells were demonstrated to be the only cell population being significantly associated (P = 0.011) with survival. Death resulting from mycosis fungoides and Sézary syndrome was significantly (P = 0.003) less frequent in patients with epidermal CD1a-positive cell densities higher than 90 cells/mm2 (optimal break point) as compared with patients with lower numbers. These results suggest that Langerhans' cells have a significant impact on prognosis of patients with mycosis fungoides and Sézary syndrome. They play an important role in the host defense mechanisms against these lymphomas rather than to favor their progression as proposed recently.

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.

Lymphocytes and macrophages of the epidermis and dermis in lesional psoriatic skin, but not epidermal Langerhans cells, are depleted by treatment with cyclosporin A

Since cyclosporin A (CsA) is an immunosuppressive agent, its beneficial effect in psoriasis suggests that immune cells may play a role in the pathogenesis and resolution of psoriasis. To determine early effects of CsA in psoriasis, we quantitated immune cells using double immunofluorescence microscopy on biopsy specimens obtained prior to therapy and after 3, 7, and 14 days of CsA therapy. CsA therapy resulted in significant reductions in the absolute number of immune cells (including T cells, monocytes/macrophages, and antigen presenting cells) contained within psoriatic skin. The effect was rapid, with over one-half of the reduction in the density of HLe1+ (human leukocyte antigen-1 positive or bone marrow derived) cells, including T cells, activated T cells, monocytes, and Langerhans cells (LCs), occurring within 3 days. Despite the overall reduction in the numbers of immunocytes in the skin, the proportion of T cells, Langerhans cells, and monocytes in relation to the total number of immune cells was unchanged with therapy, reflecting equally proportional losses of each subtype. Dermal CD1+DR+ cells (putative Langerhans cells), which are not found in normal skin but are present in lesional psoriasis skin, were virtually cleared from the papillary dermis after CsA therapy. Although absolute numbers of epidermal Langerhans cells, defined as cells expressing both CD1 (T6) and DR molecules (CD1+DR+), were also reduced after CsA, epidermal non-Langerhans CD1-DR+ cells (macrophages, activated T cells, DR- keratinocytes) demonstrated a proportionally greater decrease, with the ratio of CD1+DR+ Langerhans cells/non-Langerhans CD1-DR+ epidermal cells changing from a mean of 0.82 at baseline to 1.92 at day 14.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of OKM5 antigen on epidermal cells in mycosis fungoides plaque stage

To characterize and quantitate potential antigen-presenting cell subsets in the epidermis of patients with cutaneous T-cell lymphoma, epidermal cells in suspension were obtained from involved and uninvolved skin. Involved epidermis contained increased numbers of OKT6+HLA-DR+ Langerhans cells and a variable number of OKM5+ epidermal cells (ECs) in all mycosis fungoides (MF) patients tested (N = 14). The OKM5+ EC population from involved epidermis of MF patients were heterogeneous and comprised both OKM5+HLe1- keratinocytes and OKM5+HLe1+ leukocytes. Uninvolved epidermis, in 6 of 14 patients with MF, contained a small number of OKM5+ leukocytes; however, no OKM5+ keratinocytes were detected. Neither OKM5+ leukocytes nor OKM5+ keratinocytes were detected in the epidermis obtained from healthy controls. The increased number of potential antigen-presenting cells, that is, OKT6+HLA-DR+ Langerhans cells and OKM5+HLA-DR+ monocytic leukocytes, in the epidermis of patients with MF may be important for the activation of abnormal T cells contained within the epidermis of these patients. Such activated T cells may release gamma-interferon and induce expression of both HLA-DR and OKM5 antigens on keratinocytes. OKM5+ keratinocytes are present in the epidermis of patients with MF, but not in normal skin, and may thus play a role in the pathogenetic mechanisms of mycosis fungoides by recruitment of immunocompetent cells to the epidermis.

Electron microscopic and immunolabeling studies of the lesional and normal skin of patients with mycosis fungoides treated by total body electron beam irradiation

Biopsy specimens were taken from lesional and normal skin of nine patients with mycosis fungoides before and after total body electron beam therapy. By electron microscopy, lesional skin had one and one-half to ten times as many epidermal Langerhans cells and indeterminate cells as did the normal skin. In successfully treated lesional skin 1 month after the end of electron beam therapy, the density of epidermal Langerhans cells and indeterminate cells had decreased markedly. In incompletely resolved lesions, Langerhans cells and indeterminate cells were still at pretreatment levels. Epidermal T6 and Ia antigens showed the same pattern of response. Epidermal cell suspensions from lesional and normal skin before and after electron beam therapy were assayed for epidermal thymocyte activating factor. The values of production of this factor did not correlate with the source of the epidermal cells, response to therapy, or the patient's disease course. Skin lesions resembling xerosis and parapsoriasis and histologically lacking the criteria for mycosis fungoides appeared during clinical remissions. These nonspecific skin lesions had densities of epidermal Langerhans cells, indeterminate cells, and T6-positive and Ia-positive cells comparable to levels found in pretreatment lesional skin.

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.

Langerhans cells in the dermal infiltrate of hyperkeratosis lenticularis perstans

Typical papules obtained from a patient with hyperkeratosis lenticularis perstans (HLP) were examined by light and electron microscopy. Dense cellular infiltrate, which consisted mainly of mononuclear cells, was observed in the dermis underlying the lesion. Electron microscopic studies revealed that these cells were mostly lymphocytic cells. In addition, several Langerhans cells were found in the infiltrate, some of which were apposed to the lymphocytic cells. These findings suggested that immunologic reactions via Langerhans cells might occur in HLP and further raises a possibility that Langerhans cells might be involved in the pathogenesis of HLP.

Dendritic cells in the dermal infiltrate of Sézary syndrome

The dermal infiltrates of four patients with the Sézary syndrome were studied by electron microscopy and the data were evaluated quantitatively. The nuclear contour index of lymphocytes was calculated, and many tumour cells had an index greater than 6.5. Dendritic cells were found in all cases. The dendritic cells contained smooth and rough endoplasmic reticulum, moderately well-developed Golgi apparatus, scanty lysosomes and many thin and intermediate filaments; their surface was scalloped with numerous vesicles. Birbeck granules were not found in the cytoplasm of dendritic cells. Dendritic cells comprised 24% of infiltrating cells and were interspersed with lymphocytes; 75% of the lymphocytes were in contact with dendritic cells; 35% of the lymphocytes in contact with dendritic cells had a nuclear contour index higher than 6.5 and 76% had a nuclear contour index higher than 5. The data strongly suggest a functional relationship between lymphocytes and dendritic cells in the dermal infiltrate of Sézary syndrome. They are discussed in relation to the hypothesis that the disease is a consequence of chronic immune stimulation.

Langerhans cells in verruciform xanthomas: an immunoperoxidase study of 10 oral cases

Ten oral verruciform xanthomas were studied using an immunoperoxidase stain for S-100 protein. All cases exhibited positively stained dendritic cells among the mononuclear inflammatory cell infiltrate at the base of the lesions and to a lesser extent among the "foam cells". The foam cells were, however, negative for S-100 staining. We suggest that, based on these findings, verruciform xanthomas belong to a new category of "non-X histiocytoses" in which the presence of Langerhans cells suggests an immunologic pathogenesis.

Heterogeneity of cutaneous T-cell lymphoma. Phenotypic and ultrastructural characterization of four unusual cases

This study characterized, by means of immunocytochemistry and electron microscopy, four cases of "unusual" cutaneous T-cell lymphoma (CTCL) other than classical mycosis fungoids and Sézary syndrome. Cases 1, 2, and 4 were diffuse lymphoma of a pleomorphic type, and Case 3 was of a mixed type. Case 4 shared a feature common to pagetoid reticulosis. A fairly large number of inflammatory cells were seen in Cases 1, 3, and 4. Functionally, the neoplastic cells of Cases 1, 3, and 4 were of a helper/inducer T-cell subset, whereas those of Case 2 were of a suppressor/cytotoxic T-cell type. Epidermotropic cells with pagetoid growth in Case 4 failed to show these specific surface phenotypes, although they still retained pan T-cell markers. Neoplastic large or intermediate-sized cells revealed a marked difference in the development of cytoplasmic organelles and their nuclear profiles, ranging from a few simple indentations (Cases 2 and 3) to forms with many deep indentations (Case 1) and highly cleaved shapes (Case 4). All of these cells, however, possessed dense-cored granules located in a portion of the cytoplasm. This study indicated the clinicopathologic and immunologic heterogeneity of CTCL, which may be classified, according to the reactivity with monoclonal antibodies and the fine structural features, into subtypes that correspond to functionally distinct subsets of T-cells and their stages or types of differentiation.

Reduced epidermal Langerhans cell densities in patients with pulmonary malignancies do not correlate with anergy or nutritional status

Epidermal Langerhans cell (ELC) densities are markedly reduced in a number of clinical situations including anergic sarcoidosis patients. To help determine whether this reduction is related to the anergic or nutritional status of the patient, we examined the non-sun-exposed epidermis of 23 hospitalized patients with various malignancies (MP), 10 hospitalized control (HC) patients without malignancy, and 24 biopsies from historical control (HIC) patients. There was no significant difference in the density of HLA-DR+ ELC among HC, HIC, or patients with nonpulmonary malignancy (primary or metastatic). Six patients with pulmonary malignancy had significantly fewer HLA-DR+ and OKT6+ epidermal cells. The reason ELC densities are reduced specifically in pulmonary malignancies remains under study.

Heterogeneity of dermal OKT6+ cells in inflammatory and neoplastic skin diseases

This immunopathologic study of both normal and pathologic skin specimens (contact dermatitis [CD], lichen planus [LP], cutaneous T cells lymphoma [CTCL], and histiocytosis X [HX]) allowed as to differentiate four types of dermal OKT6+ cells: (1) cells with the same morphologic features as epidermal Langerhans cells (LCs), rarely found in either normal or pathologic dermis; (2) cells structurally similar to LCs but lacking Birbeck granules (BGs), found mainly in CD and LP; (3) larger cells rich in cytoplasmic organelles, only 5% of which contained BGs. They were especially common CTCL; and (4) cells typical of HX.

Monoclonal antibodies and cutaneous T cell lymphoma. Theoretical and practical considerations

The T cell nature of mycosis fungoides and Sézary syndrome was established a decade ago. The recent advent of monoclonal antibodies to T cells and other lymphoid subpopulations has resulted in an explosion of knowledge on the biology of this group of disorders. These reagents have increased our knowledge on thymic differentiation status, pathogenesis, the phenotype of premalignant vs malignant lymphocytic infiltrates, the identification of other previously unrecognized cells within lymphomas, and the phenotype of circulating vs skin lymphocytes. Therapeutic applications may result. These new developments are discussed.

In situ study of T-cell subpopulations in cutaneous T-cell lymphoma. Diagnostic criteria

The T-cell subpopulations present in skin biopsy specimens from 91 patients with cutaneous T-cell lymphoma (CTCL) and from 19 patients with benign lymphocytic infiltrates of the skin were examined in situ to define criteria for the differentiation of benign from malignant lymphocytic infiltrates. The monoclonal antibodies OKT 1 (pan T-cell), BE 3 (pan T-cell), OKT 4 (helper/inducer T-cell), OKT 6 (cortical thymocyte and Langerhans' cell), OKT 8 (suppressor T-cell), and OKT 10 (pan thymocyte) were used in direct or indirect immunoperoxidase reactions. Sections were examined at high magnification, and the distribution and percentage of cells reactive with each antibody were assessed. Three main patterns of staining were observed in the CTCL patients: (1) 64% of the biopsy specimens showed that 60% of the cells present in the dermis were T-cells that were OKT 1+ and BE 3+ and there was an even distribution of the different T-cell subpopulations, with 54% being OKT 4+ and 8% OKT 8+; (2) 21% patients showed selective loss of OKT 1 antigen, and 80% of these also showed loss of BE 3 antigen; and (3) 15% patients showed large numbers of OKT 8+ cells (range, 50%-90%) but the percentages of OKT 1+ and OKT 4+ cells were within the ranges seen in Group 1, indicating the presence of a population of T-cells simultaneously expressing OKT 4 (helper/inducer) and OKT 8 (suppressor) reactivity. In 95% of the CTCL patients, 3.5% OKT 6+ cells were present in the dermal infiltrate, and in 92% of patients, 3% OKT 10+ cells were present. Comparing sections from CTCL and benign dermatoses, no single diagnostic feature was identified, but helpful differentiating features were: (1) the even, rather than nodular, distribution of the T-cell subpopulation; (2) the selective loss of OKT 1 and BE 3 antigens; (3) the presence of T-cells simultaneously expressing OKT 4 and OKT 8 antigens; and (4) the presence of OKT 10+ cells.

T-cell subsets and nuclear contour index of skin-infiltrating T-cells in cutaneous T-cell lymphoma

Cases of cutaneous T-cell lymphomas including Sézary syndrome were used to evaluate nuclear contour index (NCI), nuclear cytoplasmic ratio (N/C), and helper/suppressor T-cell ratio. It was found that: (1) the average NCI measured in pan-T-cell monoclonal antibody positive cells (N = 100) is higher than that measured in non-T-cells (N = 100) in the same lesion; (2) NCI increased from erythematous stage to tumor or Sézary stage as disease process advances; (3) N/C was not significantly increased with disease process and did not correlate with NCI; (4) suppressor T-cells were significantly increased in early stages of the disease, whereas helper T-cells were dominant in late stage lesions; and (5) the majority of tumor cell infiltrating into the epidermis were helper T-cells in all stages. In control specimens from chronic and acute skin conditions in which lymphocytic infiltration is seen, cells with NCI greater than 6.5 did not exceed 20%. It is concluded that if 25% or more cells in the lesion have NCI greater than 6.5 in pan-T-monoclonal antibody positive cells, the diagnosis of CTCL is very likely. Varying numbers of OKT6 positive cells (Langerhans' cell, thymocyte) were admixed in the dermis of all cases, and had no significant correlation with the stages.

What's new in dermatopathology?

This review emphasizes the important work in dermatopathology reported in the past 3 years. In reviewing the recent contributions in the field, four areas appear to have received particular attention: (1) new information concerning the histogenesis of cutaneous tumors based on the dual functional capacities of cells; (2) the Langerhans cell and its role in inflammatory and neoplastic processes; (3) prognostic factors in stage I malignant melanoma; and (4) the use of new immunofluorescent and immunohistochemical technics as diagnostic tools in cutaneous pathology.

Antigens specified by the Tla locus are expressed on the surface of murine Langerhans cells

A monoclonal antibody against the murine thymus leukemia antigen TL, was employed to demonstrate the presence of the antigen on the surface of dendritic cells in murine epidermis of Tla-positive strains, B.10A and A.TH. Immunofluorescence and immunoperoxidase staining of EDTA-separated epidermal sheets demonstrated dendritic cells with a distribution pattern and density comparable to that noted for anti-IAk staining. Tla-negative mouse strains such as A.TL, C3H/HeJ, and C57BL/6 did not show any staining of dendritic epidermal cells. Epidermal cell suspensions similarly contained 2-4% cells with discrete surface staining with anti-TL antibody. Capping was noted in these cells. Once again positive results were noted only in appropriate Tla-positive strains. Control staining was carried out in all cases on frozen sections of thymii from mice. Thymocytes in the cortical zones and some dendritic cells at the corticomedullary junction were stained. TL antigen in mouse appears to be analogous to T-6 antigen previously detected on human Langerhans cells.

Lymphomatoid papulosis and Hodgkin's disease: are they related?

Two different characteristic types of lymphomatoid papulosis (type A and type B) can be histologically distinguished, that represent the ends of a spectrum. In the present report, two patients are described. One patient with both lymphomatoid papulosis type A and type B lesions for more than 25 years developed Hodgkin's disease (nodular sclerosing type) in the para-aortic and para-iliac lymph nodes. Histologic examination of the skin lesions in the second patient, who had Hodgkin's disease (nodular sclerosing type) in many supradiaphragmatic lymph nodes, showed the characteristic features of lymphomatoid papulosis type A. These findings, together with the results of recent immunohistochemical investigations showing many similarities between the large atypical cells in lymphomatoid papulosis type A lesions and Reed-Sternberg cells in Hodgkin's disease, support the view that lymphomatoid papulosis type A and Hodgkin's disease are closely related conditions. The results of recent studies indicate a close relationship between lymphomatoid papulosis type B and the early stages of mycosis fungoides. Accordingly, the possible relationship between lymphomatoid papulosis types A and B, mycosis fungoides, and Hodgkin's disease is discussed.

A second look at intraepithelial Langerhans cells in mycosis fungoides and related disorders. Ultrastructural study with special reference to Langerhans granules and virus-like particles

Skin biopsies of patients with small and large plaque parapsoriasis, premycotic lesions and mycosis fungoides in different stages were examined. Special attention was paid to the relationships between Langerhans cells (LC) and the neighbouring keratinocytes and lymphocytes. At the contact areas of LC and keratinocytes as well as LC and lymphocytes, particular cell membrane phenomena were observed. Aggregations of Langerhans granules and fusions of granules with LC plasma membranes were found exclusively at LC-keratinocyte interfaces. At LC-lymphocyte contact zones cell membrane appositions were seen. In all cases investigated, virus-like particles were mainly found in LC and indeterminate cells (IDC). In 3 cases lymphocytes also contained these particles. It was of particular interest that virus-like particles were observed in skin specimens of all diseases investigated. Discrimination of these particles from other cellular organelles - especially lysosomes - was difficult, however. The significance of our findings, particularly regarding to the supposed virus aetiology of cutaneous T cell lymphomas, is discussed.