CD4+ cutaneous T-cell lymphomas show the phenotype of helper/inducer T cells (CD45RA-, CDw29+)

Roles of OX40 and OX40 Ligand in Mycosis Fungoides and Sézary Syndrome

Mycosis fungoides (MF) and Sézary syndrome (SS), the most common types of cutaneous T-cell lymphoma (CTCL), are characterized by proliferation of mature CD4+ T-helper cells. Patients with advanced-stage MF and SS have poor prognosis, with 5-year survival rates of 52%. Although a variety of systemic therapies are currently available, there are no curative options for such patients except for stem cell transplantation, and thus the treatment of advanced MF and SS still remains challenging. Therefore, elucidation of the pathophysiology of MF/SS and development of medical treatments are desired. In this study, we focused on a molecule called OX40. We examined OX40 and OX40L expression and function using clinical samples of MF and SS and CTCL cell lines. OX40 and OX40L were co-expressed on tumor cells of MF and SS. OX40 and OX40L expression was increased and correlated with disease severity markers in MF/SS patients. Anti-OX40 antibody and anti-OX40L antibody suppressed the proliferation of CTCL cell lines both in vitro and in vivo. These results suggest that OX40–OX40L interactions could contribute to the proliferation of MF/SS tumor cells and that the disruption of OX40–OX40L interactions could become a new therapeutic strategy for the treatment of MF/SS.

Phenotypical Markers, Molecular Mutations, and Immune Microenvironment as Targets for New Treatments in Patients with Mycosis Fungoides and/or Sézary Syndrome

Primary cutaneous lymphomas encompass a wide spectrum of rare lymphoproliferative disorders originating in the skin, among which, mycosis fungoides (MF) is the most common subtype. The treatment of this disease is based on skin-directed therapies eventually in association with biologic response modifiers in the early phases, whereas in patients with the advanced stages, several therapeutic strategies can be used including mono and/or polychemotherapy and bone marrow transplantation. In recent years, the identification of specific markers (phenotypical, immunological, and molecular) has led to the development of several studies (including two randomized phase III trials). The results of these studies are modifying our therapeutic strategy toward a personalized treatment approach in which the clinical characteristics of the patients and tumor-node-metastasis-blood stage are considered together with the expression of specific markers (i.e., a CD30-positive expression for the use of brentuximab vedotin). This review will provide a comprehensive scenario of the main phenotypical, molecular, and immunological markers related to MF pathogenesis and disease evolution, which could represent the target for the development of innovative effective treatments in this disease.

Aberrant CD137 ligand expression induced by GATA6 overexpression promotes tumor progression in cutaneous T-cell lymphoma

CD137 and its ligand, CD137L, are expressed on activated T cells and antigen-presenting cells, respectively. Recent studies have shown that CD137L and CD137 are aberrantly expressed by tumor cells, especially in some hematopoietic malignancies, and interactions between these molecules on tumor cells promote tumor growth. In this study, we investigated the roles of CD137L and CD137 in cutaneous T-cell lymphoma (CTCL), represented by mycosis fungoides and Sézary syndrome. Flow cytometric analysis showed that primary Sézary cells and CTCL cell lines (Hut78, MyLa, HH, SeAx, and MJ) aberrantly expressed CD137L. CD137L expression by tumor cells in CTCL was also confirmed by immunohistochemistry. Anti-CD137L-neutralizing antibody inhibited proliferation, survival, CXCR4-mediated migration, and in vivo growth in CTCL cell lines through inhibition of phosphorylation of AKT, extracellular signal-regulated kinase 1/2, p38 MAPK, and JNK. Moreover, suppression of CD137L signaling decreased antiapoptotic proteins Bcl-2 and phosphorylated Bad. We also explored the transcription factor regulating CD137L expression. Because GATA6 has been proposed as an oncogene in many types of tumors with aberrant CD137L expression, we examined GATA6 expression and the involvement of GATA6 in CD137L expression in CTCL. DNA hypomethylation and histone acetylation induced GATA6 overexpression in CTCL cells. Furthermore, chromatin immunoprecipitation, luciferase reporter assay, and knockdown by short hairpin RNA showed that GATA6 directly upregulated CD137L expression. Inhibition of GATA6 resulted in decreased survival and in vivo growth in CTCL cells. Collectively, our findings prompt a novel therapeutic approach to CTCL based on the discovery that the GATA6/CD137L axis plays an important role in the tumorigenesis of CTCL.

Interleukin-13 is overexpressed in cutaneous T-cell lymphoma cells and regulates their proliferation

Cutaneous T-cell lymphomas (CTCLs) primarily affect skin and are characterized by proliferation of mature CD4(+) T-helper cells. The pattern of cytokine production in the skin and blood is considered to be of major importance for the pathogenesis of CTCLs. Abnormal cytokine expression in CTCLs may be responsible for enhanced proliferation of the malignant cells and/or depression of the antitumor immune response. Here we show that interleukin-13 (IL-13) and its receptors IL-13Rα1 and IL-13Rα2 are highly expressed in the clinically involved skin of CTCL patients. We also show that malignant lymphoma cells, identified by the coexpression of CD4 and TOX (thymus high-mobility group box), in the skin and blood of CTCL patients produce IL-13 and express both receptors. IL-13 induces CTCL cell growth in vitro and signaling through the IL-13Rα1. Furthermore, antibody-mediated neutralization of IL-13 or soluble IL-13Rα2 molecules can lead to inhibition of tumor-cell proliferation, implicating IL-13 as an autocrine factor in CTCL. Importantly, we established that IL-13 synergizes with IL-4 in inhibiting CTCL cell growth and that blocking the IL-4/IL-13 signaling pathway completely reverses tumor-cell proliferation. We conclude that IL-13 and its signaling mediators are novel markers of CTCL malignancy and potential therapeutic targets for intervention.

The influence of STAT5 antisense oligodeoxynucleotides on the proliferation and apoptosis of selected human cutaneous T-cell lymphoma cell lines

STAT5 (signal transducers and activators of transcription) are suggested to play a role in the pathogenesis of leukaemia and lymphoma; however, their influence on the growth of cutaneous T-cell lymphoma cells is not clear enough. The aim of our study was to analyse the function of STAT5 proteins in the proliferation and apoptosis of selected cutaneous T-cell lymphoma cell lines (HUT 78; PB-1; HUT 102B), using antisense oligodeoxynucleotide (ODN) strategy. RT-PCR and Western blot were applied to analyse the expression of STAT5 after incubation with antisense ODN (AS ODN). The effect of ODN pretreatment on the cell clonogenecity was analysed in methylcellulose cultures. The process of apoptosis was estimated using two different flow cytometry (FACScan) methods: (1) combined Annexin V/propidium iodide staining, (2) the TUNEL method. Perturbation of STAT5 expression reduced the proliferation of the PB-1 cells after a 24-h exposure to antisense ODNs. Prolonged exposure (72 h) decreased the growth of each examined cell line, especially after antisense STAT5A (AS STAT5A) treatment. Incubation with AS STAT5 induced apoptosis in the population of HUT 78 and PB-1 cells. STAT5s may play a significant role in the growth and the process of apoptosis of selected human cutaneous T-cell lymphoma cells.

Establishment of a mouse xenograft model for mycosis fungoides

Mycosis fungoides (MF) is the most frequent variant of cutaneous T-cell lymphomas (CTCLs). MF primarily involves the skin initially with patches and plaques. In later stages, cutaneous tumors develop and tumor cells may spread to lymph nodes and finally to visceral sites. Here, we describe an animal model for MF in immune-deficient nude mice, using the CTCL cell line MyLa. Subcutaneous transplantation of MyLa cells leads to the formation of cutaneous tumors in 80% of the mice (50/60 total). Spread of tumor cells to visceral sites was detected by immunohistochemistry and polymerase chain reaction (PCR)-based detection of specific T-cell receptor-gamma rearrangement. MyLa cells were found circulating in the blood, lymph nodes, and in blood vessels of heart, kidney, lung, and liver. In lung and liver tissue, tumor cells presented perivascular invasion, but no large secondary tumors developed. The nude mouse model described here will be a valuable test system for new therapeutic approaches for the treatment of MF and opens the unique opportunity to study the disease in vivo.

Polyclonal expansion of T cells with the TCR Vbeta type of the tumour cell in lesions of cutaneous T-cell lymphoma: evidence for possible superantigen involvement

The involvement of superantigens in the pathology of cutaneous T-cell lymphomas (CTCL) has been suggested before, but without unequivocal evidence for superantigen activity in the patients. Seeking evidence for superantigen activity we analysed clones and microdissected single cells isolated from the epidermis of early-stage lesions of a CTCL patient for their T-cell receptor (TCR) V beta expression and TCR V gamma gene rearrangements. The vast majority of these T cells expressed the TCR V beta family type of the tumour. From their TCR gamma gene rearrangements, however, these cells were polyclonal. The tumour cell clone accounted for about 60% of these cells, about 40% were of heterogeneous origin. This dominance of a single V beta family in the polyclonally expanded dermal T-cell populations implies superantigen activity in the CTCL lesions.

The relevance of peripheral blood T-helper 1 and 2 cytokine pattern in the evaluation of patients with mycosis fungoides and Sézary syndrome

BACKGROUND

There is evidence that a T-helper (Th) 2 cytokine pattern dominates in the peripheral blood as well as in tissue of patients with Sézary syndrome (SS), and that the malignant clone is of Th2 phenotype. However, there are conflicting studies on the cytokine pattern in the peripheral blood in different stages of cutaneous T-cell lymphoma (CTCL).

OBJECTIVES

To examine, by means of flow cytometry (FC), the Th1/Th2 cytokine profile [cytoplasmic interferon (IFN)-gamma/interleukin (IL)-4] in peripheral blood T cells from patients with mycosis fungoides (MF) and SS, the most common forms of CTCL, and to correlate their expression with clinical stage, clonality and T-cell immunophenotype changes in order to evaluate their relevance in CTCL progression.

METHODS

We investigated by FC the percentage of CD3+ T cells expressing cytoplasmic IFN-gamma and IL-4 after stimulation in blood specimens of 43 CTCL patients (32 stage I-II and 11 stage III-IV), eight of whom were erythrodermic. Next, we compared cytoplasmic IFN-gamma and IL-4 expression between patients of different stages and controls, and correlated our findings to T-cell receptor (TCR)-gamma gene rearrangement, used as a marker of clonality, and changes in T-cell immunophenotype (CD4+, CD8+, CD4+/CD7-, CD4+/CD25+) and natural killer cells. Polymerase chain reaction amplification of the TCR-gamma gene was performed in 41 blood and 26 skin specimens. We also examined the cytokine expression pattern in patients with erythrodermic MF and SS.

RESULTS

A significantly higher frequency of CD3+/IL-4+ T cells was found in late (III-IV) compared with early (I-II) CTCL patients (P = 0.002) or controls (P < 0.001). There were significant positive correlations between the percentages of CD3+/IL-4+ and the percentages of CD3+/CD4+ T cells (r = 0.385, P = 0.05), CD4+/CD7- T cells (r = 0.335, P < 0.05) and CD4+/CD25+ T cells (r = 0.433, P = 0.01); there was a negative correlation between the percentages of CD3+/IL-4+ and CD3+/CD8+ T cells (r = -0.463, P = 0.005) and a positive correlation between the percentages of CD3+/IFN-gamma+ and CD3+/CD8+ T cells (r = 0.368, P = 0.02). Increased percentages of CD3+/IL-4+, CD3+/CD4+ and CD4+/CD7- T lymphocytes were associated with the presence of clonality (P = 0.025, P < 0.001 and P = 0.0031, respectively). All independent variables showed a statistically significant difference between SS and erythrodermic MF patients, or controls, apart from cytoplasmic IL-4, which was high both in erythrodermic MF and SS patients compared with controls (P = 0.003 and P = 0.008, respectively). In multiple regression logistic analysis, the probability of belonging to advanced CTCL stages was associated only with increased cytoplasmic IL-4 (P = 0.007, odds ratio 1.13, 95% confidence interval 1.033-1.229).

CONCLUSIONS

Increased T-cell cytoplasmic IL-4 is more frequent in late CTCL stages, correlates with T-cell immunophenotype changes found in advanced disease and is associated with clonality. Increased cytoplasmic IL-4 is frequent both in erythrodermic MF and SS patients, in contrast to other variables found increased only in SS, suggesting that IL-4 may be an early indicator of disease progression. Moreover, our results show that increased cytoplasmic IL-4 is the sole predictor of advanced CTCL disease and confirm the relevance of FC determination of IL-4 in the routine evaluation of CTCL cases.

Diagnostic and prognostic importance of T-cell receptor gene analysis in patients with Sézary syndrome

BACKGROUND

Sézary syndrome (SS) is characterized by erythroderma, peripheral lymphadenopathy, and circulating Sézary cells and is clinically heterogeneous.

METHODS

T-cell receptor (TCR) gene analysis was performed using DNA extracted from peripheral blood mononuclear cells from 74 patients, and the results were correlated with a variety of other diagnostic parameters and patient outcomes.

RESULTS

Two groups were identified: 66 patients with clonal TCR gene rearrangement (clonal patients) detected with Southern blot analysis and/or polymerase chain reaction/single-strand conformational polymorphism analysis and 8 patients with no clonal rearrangement detected (nonclonal patients) using either technique. Clonal patients were compared with nonclonal patients. The following median blood parameters were significantly greater in the clonal group: total white cell count (13.7 10(9)/L vs. 9.6 10(9)/L), lymphocyte count (4.9 10(9)/L vs. 2.2 10(9)/L), absolute Sézary count (3.22 10(9)/L vs. 0.99 10(9)/L), CD4 count (3.17 10(9)/L vs. 1.36 10(9)/L), and CD4:CD8 ratio (15.86 vs. 3.21). An expanded population of T-cells of a specific TCR variable beta subset was detected in 7 of 36 clonal patients and in 1 of 4 nonclonal patients. Cytogenetic analysis of peripheral blood from 1 nonclonal patient and 6 clonal patients was normal. The median survival from the time of diagnosis was 45 months in the clonal group, and 40 of 49 deaths were cutaneous T-cell lymphoma (CTCL)-related, whereas 3 deaths in the nonclonal group were unrelated to CTCL (P < 0.01; log-rank test). Multivariate proportional hazards analysis showed that the absolute Sézary count and lymph node status were independent prognostic variables (P = 0.016 and P = 0.036, respectively).

CONCLUSIONS

TCR gene analysis defines a distinct clinicopathologic group of patients with SS. Clonal patients have a poor prognosis and are likely to die from leukemia/lymphoma, whereas nonclonal patients may have a reactive, inflammatory T-cell disorder. The authors suggest that the definitive diagnostic criteria for patients with SS should include the presence of a clonal TCR gene rearrangement.

The relevance of the CD4+ CD26- subset in the identification of circulating Sézary cells

BACKGROUND

The lack of specific markers for the phenotyping of circulating neoplastic T cells in Sézary syndrome (SS) patients makes it difficult both to ascertain the presence of clonal cells and to quantify the tumour burden in the peripheral blood. In previous reports we showed that the lack of CD26 (dipeptidyl-aminopeptidase IV) is a characteristic feature of circulating Sézary cells (SC).

OBJECTIVES

The purpose of this study was to ascertain, by means of high-resolution two-, three- or four-parameter flow cytometry, the relationship between CD26 expression on peripheral blood lymphocytes and peripheral blood involvement in cutaneous T-cell lymphoma patients and to assess its significance in SS diagnosis.

METHODS

The patient population included 52 SS patients, 151 mycosis fungoides (MF) patients at different clinical stages (including 14 with blood involvement, B1-MF), 88 patients with erythrodermic inflammatory skin diseases (EISD) and 72 healthy donors (HD). CD26+ values were available in all cases, whereas CD4+ CD26- level measurement was performed in 23 SS, 141 MF, 71 EISD and 72 HD.

RESULTS

CD4+ CD26- percentage values were higher than 30% in all but one B1-MF and higher than 40% in all SS cases, whereas HD, EISD and B0-MF patient values were always lower than 30%. A statistically significant difference was found in both CD26- and CD4+ CD26- percentage and absolute values between SS and HD, EISD and B0-MF patients. The CD26- and CD4+ CD26- percentage values (but not the absolute values) were significantly higher in B1-MF compared with HD, EISD and B0-MF patients (P < 0.001). Moreover, CD26- absolute values and CD4+ CD26- percentage and absolute values were significantly higher in SS than in B1-MF (P < 0.001). A statistically significant direct relationship was found between CD4+ CD26- percentage values and the percentage of circulating SC within the lymphoid population in SS and B1-MF (r = 0.77; P < 0.001). The lack of CD26 was confirmed on phenotypically clonal cells in patients with an expanded circulating TCRvbeta population or a T-cell antigen loss. Sorted CD4+ CD26- cells from both SS patients and HD showed the characteristic cerebriform nuclei of SC.

CONCLUSIONS

We feel that a CD4+ CD26- percentage value higher than 30% of peripheral blood lymphocytes could correctly identify the presence of peripheral blood involvement in SS and MF patients.

Sézary T-cell activating factor is a Chlamydia pneumoniae-associated protein

We previously identified a protein that was stimulatory for malignant Sézary T cells, termed Sézary T-cell activating factor (SAF). However, the identity of this protein has not been fully elucidated, nor has it's role been determined in the pathogenesis of cutaneous T-cell lymphoma (CTCL). The basis for epidermotropism and proliferation of malignant cells in the skin of patients with CTCL is unknown. Using a monoclonal antibody inhibitory for SAF activity, we demonstrated that SAF is present in the skin of 16 of 27 samples from patients with mycosis fungoides, the predominant form of CTCL. In this report, the SAF determinant is demonstrated to be associated with Chlamydia pneumoniae bacteria by immunohistochemistry, immunoelectron microscopy, and culture analysis. Reactivity of antibodies against an outer membrane protein of C. pneumoniae or against the lipopolysaccharide of Chlamydiae spp. demonstrated that these determinants are coexpressed in 90% of the SAF-positive samples. We confirmed the presence of C. pneumoniae DNA and RNA in the skin by PCR and reverse transcription-PCR and by sequence analysis of the PCR products. The expression of the C. pneumoniae antigens and SAF appears to be associated with active disease in that C. pneumoniae antigens were absent or greatly diminished in the skin of three patients examined after Psoralen and long-wave UVA radiation treatment. Our results suggest that SAF is a Chlamydia-associated protein and that further investigation is warranted to determine whether SAF and C. pneumoniae play a role in the pathogenesis of CTCL.

Detection of clonal T cells in cutaneous T cell lymphoma by polymerase chain reaction: comparison of mutation detection enhancement-polyacrylamide gel electrophoresis, temperature gradient gel electrophoresis and fragment analysis of sequencing gels

Cutaneous T cell lymphomas (CTCL) can be differentiated from benign inflammatory dermatoses by the demonstration of clonal T cells in skin biopsy. As a marker of the T cell clonality, the rearrangement of the T cell receptor (TCR) genes is amplified by polymerase chain reaction (PCR) and subsequently analyzed by several electrophoresis techniques. Since the validity of this approach depends substantially on the separating capacity of the applied electrophoresis technique, we investigated in the present study the lower detection limit and the sensitivity of heteroduplex-loaded polyacrylamide gel electrophoresis on MDE (mutation detection enhancement) gels (HD-MDE PAGE), of heteroduplex-loaded temperature gradient gel electrophoresis (HD-TGGE) and fragment analysis (FA) on sequencing gels. Genomic DNA from formalin-fixed, paraffin-embedded skin biopsies of 53 CTCL specimens and 27 samples of benign dermatoses was analyzed by TCRy PCR followed by electrophoretic separation. Clonality was detected by HD-MDE PAGE in 22, by HD-TGGE in 34, and by FA in 33 of the 53 CTCL cases. Additionally, FA revealed an oligoclonal fragment profile in seven CTCL specimens. In the 27 samples from benign dermatoses, HD-MDE PAGE and HD-TGGE showed the expected polyclonal pattern in 26, and FA in 25 specimens. HD-TGGE and FA detected a clonal pattern down to a dilution of 10(3) monoclonal cells in 10(6) peripheral blood mononuclear cells (PBMC), while HD-MDE PAGE revealed a detection limit of 10(4) monoclonal cells in 10(6) PBMC. In conclusion, HD-TGGE and FA possess a higher sensitivity and lower detection limit than HD-MDE PAGE. Therefore, both former techniques are useful tools for the routine diagnostic procedure. With regard to time and cost, we recommend HD-TGGE.

Aberrant responses of human lymphocytic neoplasms to cytokine regulation

Studies in this laboratory have recently focused on two hemic neoplasms: B cell chronic lymphocytic leukemia (B-CLL) and a T cell disorder, Sézary syndrome. These tumors do not have consistent cytogenetic or molecular genetic alterations, and so we have concentrated on their response to and production of various regulatory cytokines. Although B-CLL cells show variable proliferative responses when exposed to transforming growth factor beta (TGF beta), these cells have consistently shown resistance to the pro-apoptotic effects of this cytokine. Also, interleukin 4 (IL4), IL5, and interferon-gamma (IFN gamma) all show a consistently increased protective effect against apoptosis in B-CLL cells as compared to normal human B cells. Thus, a defect in apoptosis appears to be an important factor in the pathogenesis of CLL. By contrast, the neoplastic T cells of Sézary syndrome show a consistent resistance to the antiproliferative effects of TGF beta, suggesting that aberrant proliferation is more important than apoptosis in this disorder. In both neoplasms, we have shown that the defective responses to cytokines are in some instances related to alterations in receptor expression, but this has not been true in all circumstances, and other stages in the signaling pathways are being investigated. As we define more precisely the specific defects that contribute to the clonal expansion of these neoplasms, the findings may ultimately lead to improved clinical control of these disorders.

Genotraumatic T cells and cutaneous T-cell lymphoma. A causal relationship?

Mycosis fungoides, or cutaneous T-cell lymphoma (CTCL), is a T-cell mediated chronic inflammatory skin disease, which can occasionally progress with a variable time course to a fatal lymphoma or to a leukaemic form called Sézary's syndrome. Extensive research into CTCL has not yet elucidated the primary pathophysiological mechanisms. Immunohistological studies are so far less helpful than expected in establishing early diagnosis and prognosis of the disease. The proposition that an exogenous virus is the cause of CTCL has not been substantiated. Karyotypic analysis of lymphocytes from the skin and blood of patients with CTCL have shown the existence of several genetically aberrant T-cell clones in the same patient. These changes are discussed as potential primary events for the development of CTCL. The hypothesis is put forward that the development of genotraumatic T lymphocytes is involved in the progression of the disease.

Expression of CD45RA (naive) and CD45RO (memory) antigens in T-acute lymphoblastic leukaemia

We have determined the distribution of CD45RO (memory) and CD45RA (naive) antigens in the bone marrow blasts from 25 patients with T-acute lymphoblastic leukaemia (T-ALL). Four groups of patients were identified on the basis of reactivity with specific antibodies by flow cytometric analysis: (a) CD45RA-/CD45RO+ (16 patients): four CD4-/CD8+, seven CD4+/CD8+ and five CD4-/CD8-; (b) CD45RA+/CD45RO- (three patients): three CD4-/CD8-; (c) five CD45RA-/CD45RO-: one CD4+/CD8-; one CD4-/CD8+; three CD4+/CD8+; (d) CD45RA+/CD45RO+ (one case): CD4+/CD8-. There was no correlation between the expression of the naive and the memory phenotypes and the presence of CD4, CD8 or any other antigen except the CD10 antigen which was expressed by all CD45RA-/CD45RO- patients. The predominance of the CD45RA-/CD45RO+ phenotype (65%) and the low incidence of the hybrid phenotype CD45RA+/CD45RO+ (5%) in T-ALL, differs from the results reported by others for chronic or prolymphocytic T-cell leukaemias, in which the simultaneous expression of these maturational antigens was detected in approximately half of the cases.

Cell-bound IgE and increased expression of Fc epsilon-receptors on dendritic cells in cutaneous infiltrates of mycosis fungoides

Skin biopsies of 31 non-atopic patients, 20 with mycosis fungoides, six with psoriasis and five with contact dermatitis, and of five non-atopic healthy controls were compared for the presence of cell-bound IgE and vacant IgE binding sites. IgE+ cells were demonstrated in the cutaneous infiltrate of nine (45%) patients with mycosis fungoides, two (33%) with psoriasis and one (20%) with contact dermatitis. Following pre-incubation of skin sections with IgE myeloma protein to saturate vacant IgE-binding sites, 14 out of 16 patients (88%) with stage I mycosis fungoides, five (83%) patients with psoriasis and one (20%) with contact dermatitis showed an increase in the number of IgE+ cells. While cell-bound IgE was positively related to serum IgE levels the expression of IgE-binding sites was not. All IgE+ cells were HLA-DR+ dendritic cells identified as either macrophages (CD68+, CD14+) or Langerhans cells (CD1+). Skin biopsies of non-atopic healthy controls or clinically uninvolved skin in mycosis fungoides had neither any IgE+ cells nor any vacant binding sites. Inhibition studies with IgG1, IgG4 and IgE myeloma proteins as well as with several enzymatic fragments of IgE demonstrated that IgE interacted with Fc epsilon-receptors through isotype-specific structures on the Fc epsilon-fragment. Four anti-CD23 monoclonal antibodies, however, were unable to stain vacant Fc epsilon-receptors nor could they block IgE-binding. We hypothesize that locally-secreted lymphokines, like IL-4 or interferon-gamma, induce Fc epsilon-receptors on dendritic cells in the cutaneous infiltrate and that these receptors become occupied in parallel with elevated serum IgE levels.