Induction of lymphocyte differentiation by epidermal cultures

Role of Lymphoid Structure in Skin Immunity

The skin is the outermost organ of the body and is exposed to many kinds of external pathogens. To manage this, the skin contains multiple types of immune cells. To achieve sufficient induction of cutaneous adaptive immune responses, the antigen presentation/recognition in the skin is an essential process. Recent studies have expanded our knowledge of how T cells survey their cognate antigens in the skin. In addition, the formation of a lymphoid cluster, named inducible skin-associated lymphoid tissue (iSALT), has been reported during skin inflammation. Although iSALT may not be classified as a typical tertiary lymphoid organ, it provides specific antigen presentation sites in the skin. In this article, we provide an overview of the antigen presentation mechanism in the skin, with a focus on the development of iSALT and its function.

Novel insights into the role of immune cells in skin and inducible skin-associated lymphoid tissue (iSALT)

The skin is equipped with serial barriers that provide rapid and efficient protection against external intruders. Beneath the epidermal physical barriers of the stratum corneum and the tight junctions, the integrated immune systems in both the epidermis and the dermis act in a coordinated manner to protect the host. This “immunological” barrier is composed of various cells, including skin-resident cells, such as keratinocytes, dendritic cells, tissue-resident macrophages, resident memory T cells, mast cells, and innate lymphoid cells. Additionally, infiltrating memory T cells, monocytes, neutrophils, basophils, and eosinophils are recruited in support of the host immunity.

In addition to discussing the role of each of these cellular populations, we describe the concept of skin associated lymphoid tissue (SALT), which reminds us that the skin is an important component of the lymphatic system. We further describe the newly discovered phenomenon of multiple cell gathering under skin inflammation, which can be referred to as inducible SALT (iSALT). iSALT contributes to our understanding of SALT by highlighting the importance of direct cell-cell interaction in skin immunity.

Vascularized composite allotransplantation: towards tolerance and the importance of skin-specific immunobiology

PURPOSE OF REVIEW

Vascularized composite allotransplantation (VCA) is increasingly utilized in the restoration of complex injuries and tissue loss. Acute skin-targeted rejection episodes are common and concerns remain regarding the risks of conventional immunosuppression. We review current immunosuppressive regimens for VCA, progress with immunomodulatory and tolerance protocols, and highlight recent advances in cutaneous immunobiology which will have significant implications for future development in the field.

RECENT FINDINGS

Advances in induction protocols have demonstrated effective prevention of early graft loss in hand transplantation, although long-term outcomes are still pending. Furthermore, recent findings in leukocyte populations within the skin and their mechanisms of communication reveal that considerable numbers of resident T-effector memory cells, including a T-regulatory subset, exist, and that epidermal Langerhans' cells communicate with these cells, mediating both immunity and tolerance to maintain skin homeostasis.

SUMMARY

The majority of VCA centers utilize antibody-mediated induction, followed by double or triple-agent maintenance immunosuppression. A clinical trial of a minimal-immunosuppression protocol based on bone marrow infusion reports encouraging interim results, but long-term follow-up will be required. Skin remains the primary target of rejection in VCA. New data demonstrate extensive T-cell memory resident in skin, and complex interactions between these cells and epidermal Langerhans' cells will have implications for VCA rejection and tolerance, and warrant further investigation in the allogeneic setting.

Skin as a peripheral lymphoid organ: revisiting the concept of skin-associated lymphoid tissues

Antigen presentation to T cells is essential for the induction of adaptive immunity. This event takes place not solely in the lymph node (LN) but also in the skin. Recent in vivo trafficking studies using Kaede-transgenic mice reveal that skin-homing effector memory T cells alter their effector function and homing ability by transitioning to a central memory T cell-like phenotype through antigen recognition that occurs in the skin. In addition, these cells travel back and forth between the skin and draining LNs. These studies are evocative of the classic concept of skin-associated lymphoid tissues and underscore the critical role of skin as a peripheral lymphoid organ.

The distribution of lymphocyte subpopulations in normal and acanthotic ovine skin

The prevalence and distribution of lymphocyte subpopulations in normal and acanthotic ovine skin were investigated using monoclonal antibody immunocytochemistry. CD8+ cells were predominant in the epidermis of both normal and acanthotic skin, but were CD8+ cells, CD4+ cells and T19+ cells infrequent in normal epidermis. Within the dermis of normal skin, there were significantly greater numbers of CD4+ and T19+ cells situated around the superficial dermal vessels than in any other region examined. The majority of the CD8+ cells adjoined vessels, but the proportion that did not was greater for CD8+ than for CD4+ or T19+ cells. The CD4+ and CD8+ subsets were represented equally in adnexa. T cells were of memory phenotype. B cells and naive T cells, both of which express the CD45RA antigen, were rarely seen and tended to be associated with vessels in both normal and acanthotic skin. None of the T19+ cells (which are gamma delta+) resembled the dendritic gamma delta cells seen in murine epidermis. Acanthotic skin was strikingly different to normal skin. There was a greater abundance of T cells, particularly CD4+ cells, in acanthotic epidermis and the numbers of CD8+ and T19+ cells, and to a greater extent CD4+ cells, were greater at the dermal-epidermal junction. There were more CD4+ and CD8+ cells in the superficial dermal stroma of acanthotic skin. Within the dermis of acanthotic skin, T cells were concentrated near vessels but the apportioning of T cells between stromal/adnexal and vessel-associated sites differed from normal. Such observations suggest that migration away from perivascular sites and into the stroma may be controlled separately for subregions of skin and for each T cell subset. The role of this altered nonrandom migration of T cells in skin chronically exposed to ultra violet radiation is uncertain.

Thymus-independent generation of Thy-1+ epidermal cells from a pool of Thy-1- bone marrow precursors

Thy-1+ dendritic epidermal cells (Thy-1+ DEC) and immature thymocytes share several phenotypic features: CD45+, Thy-1+, asialo-GM1+, CD3+, CD4-, and CD8-. In view of this similarity, it has been suggested that the epidermis may be a site of either post-thymic or extra-thymic T-cell development. In order to address this issue, we used C3H/He/Han (Thy-1.2)----AKR/Ola (Thy-1.1) radiation bone marrow chimeras. Animals were first either thymectomized or sham-thymectomized, then lethally irradiated (750R) and, finally, reconstituted with allogeneic bone marrow cells previously depleted of Thy-1-bearing cells. Six weeks after bone marrow transplantation, spleens and lymph nodes of sham-treated animals, but not of thymectomized animals, contained large numbers of CD3+ donor-type Thy-1+ cells. The epidermis of both thymectomized and sham-treated animals contained not only many recipient-type CD3+, Thy-1+ DEC, but also small numbers of CD3-, donor-type Thy-1+ cells. After 4 months, the frequency of donor cells had greatly increased, but they still lacked CD3 antigens. Most of the donor cells had a rounded shape, but some exhibited a dendritic configuration. These results demonstrate that Thy-1- bone marrow-derived precursors of Thy-1+ DEC can migrate to the epidermis without thymic influence and yet acquire Thy-1 antigens during their journey. Although donor-type Thy-1+ epidermal cells failed to mature into CD3+ dendritic epidermal cells, the experimental model used in this study may be a versatile tool for studying the influence of thymic and extrathymic epithelia on T-cell maturation.

Genotypic analysis of T-cell clones derived from cutaneous T-cell lymphoma lesions demonstrates selective growth of tumor-infiltrating lymphocytes

The nature of T cells contained within cutaneous lesions of cutaneous T-cell lymphoma (CTCL) has not been studied at the clonal level. T cells extracted from skin lesions of two CTCL patients were cloned by limiting dilution and propagated in interleukin-2 (IL-2) containing medium with periodic lectin stimulation. Twelve T-cell clones were derived from each patient. In both cases, genotypic analysis of the T-cell clones revealed that these clones had T-cell receptor (TCR) beta- and gamma-chain gene rearrangements distinct from the predominant, presumably malignant, clone present in the skin, lymph nodes, or blood. This suggests that they were derived from presumably reactive (non-malignant) T cells. Furthermore, these clones had gene rearrangements different from each other, indicating their multiple clonal origins. The failure to propagate in vitro the CTCL T-cell clone suggests that CTCL cells may have growth requirements different from normal T cells. Thus, conventional T-cell culturing methods using IL-2 and lectins as mitogen may selectively propagate the presumably reactive T cells contained within the skin lesions. The ability to selectively grow these reactive lesional T cells (so-called tumor infiltrating lymphocytes) raises the possibility that these cells could be used in adoptive immunotherapy.

Histologic and electron microscopic characterization of the antiperinuclear factor antigen

The presence of the antiperinuclear factor, an autoantibody that recognizes cytoplasmic antigens, was detected in sera from patients with rheumatoid arthritis (59%), seronegative rheumatoid arthritis (36%), systemic lupus erythematosus (46%), systemic sclerosis (26%), and in nonautoimmune controls (10%). The antigenic perinuclear granules were found in the stratum intermedium layer of the buccal mucosa. Granules exhibited histologic features of nucleoproteins, stained for ribonucleoprotein, and showed the ultrastructural characteristics of aggregated rough endoplasmic reticulum. The antiperinuclear factor may recognize a common autoantigen in connective tissue disease.

The role of adhesion molecules in epithelial-T-cell interactions in thymus and skin

Interaction of T lymphocytes with other cell types is important for normal T-cell development and function. Recently, a number of adhesion molecules important in T-cell interactions with other cell types have been defined. In this paper we review the role of two adhesion pathways, CD2/LFA-3 and LFA-1/ICAM-1, in T-cell interactions with epithelial cells of the thymus and skin. While thymic epithelium-T-cell interactions were mediated by both the LFA-1/ICAM-1 pathway and the CD2/LFA-3 pathway, epidermal-T-cell interactions were mediated primarily by the LFA-1/ICAM-1 pathway. Although ICAM-1 was not expressed in vivo on epidermal keratinocytes in normal skin, ICAM-1 was expressed by epidermal keratinocytes at the site of T-cell infiltration in inflammatory dermatitis. ICAM-1 was expressed in vivo on thymic epithelium. Both LFA-3 and ICAM-1 were expressed on epithelial cells of thymus and skin early on in fetal ontogeny. These antigen-independent adhesion molecules play an important role in the cell-cell interactions associated with T-cell differentiation and function.

T cell receptor beta-chain gene rearrangement without gamma-chain gene rearrangement in cutaneous T cell lymphoma: an unusual finding

T cells from the blood and skin of a patient with cutaneous T cell lymphoma demonstrated rearrangement of the T cell receptor beta-chain gene in the absence of rearrangement of the gamma-chain gene. To our knowledge, this has not been previously reported. This finding was unexpected in light of prevailing concepts of T cell ontogeny. Potential explanations for it are discussed.

Phorbol ester regulation of terminal deoxynucleotidyl transferase, proliferation, and TcR alpha in a pre-T cell line

Terminal deoxynucleotidyl transferase (TdT) is a template-independent DNA polymerase that is transiently expressed during the normal development of T and B lymphocytes. Phorbol 12-myristate 13-acetate (PMA) has been reported to induce maturation-like changes, including the loss of TdT, in many leukemic cell lines. We investigated the mechanism of TdT repression by PMA in an early thymocyte-like cell line, RPMI 8402. At a concentration of 8 nM, PMA caused both repression of TdT synthesis and arrest of proliferation. At greater concentrations of PMA, these same changes initially occurred, but then cell proliferation resumed, and TdT was reexpressed. At both 8 and 160 nM PMA, TdT biosynthesis and TdT mRNA became undetectable within 8 hours, while cell proliferation and DNA synthesis were not significantly reduced until 16 hours. Growth arrest induced by serum starvation did not result in a similar reduction of TdT RNA even after 48 hours. With 160 nM PMA, TdT mRNA could be detected again by 24 hours, and proliferation resumed. Transcription run-off assays indicated that TdT RNA synthesis ceased within 1 hour after exposure to both 8 and 160 nM PMA. T cell receptor alpha (TcR alpha) RNA was induced when TdT RNA was repressed. TcR beta RNA levels were unchanged, and TcR gamma RNA was up-regulated. TdT gene repression and modulation of cell proliferation as well as induction of TcR gene expression are normal events during intrathymic T cell maturation. This cell model provides a system for analyzing the molecular regulation of these significant developmental events.

Effect of aging on epidermal dendritic cell populations in C57BL/6J mice

The density and function of epidermal dendritic cell populations were investigated in aged C57BL/6J mice. The densities of both Langerhans cells (LC) and Thy-1+ dendritic epidermal cells were found to decrease with age. Epidermal cell suspensions from aged mice showed impaired immunologic function as assessed in vitro by the skin-lymphocyte reaction assay and by measuring the ability of epidermal cell suspensions to stimulate the proliferation of sensitized T cells in the presence of the sensitizing antigen. However, the capacity of LC to transport antigen from the skin to the draining lymph nodes was found in vivo to be comparable to that of young mice. Results of transplantation of bone marrow cells from young and old donors into irradiated recipients indicate that the decreased Langerhans cell density found in old mice may result from a deficiency in Langerhans cell bone marrow progenitors.

Cutaneous lymphohistiocytic infiltrates in patients with hypogammaglobulinemia

Six patients (5 to 15 years of age) with hypogammaglobulinemia had scattered papular lesions in association with widespread dermatitis. These disfiguring lesions were a portal of entry for secondary infections and led to social withdrawal. Biopsy specimens from the papules demonstrated dense lymphohistiocytic infiltrate limited to the dermis. Infectious causes (bacterial, fungal, and viral) were excluded. The skin lesions failed to respond to conventional treatment, including topical corticosteroids. Replacement therapy with monthly infusions of high doses of immune serum globulin resulted in gradual improvement and ultimate clearing of the lesions. This unusual skin abnormality, which is unresponsive to traditional treatment, may provide the earliest clue to the presence of hypogammaglobulinemia.

Histogenesis of malignant melanoma of the skin: the role of lymphocytes in the transformation of tissue developmental units

It is proposed that the completion of both growth and differentiation, in highly specialized progressively evolving multicellular organisms, is achieved throughout two separated but sexually interacting populations of cells (bi-clonal model): 1) the germ line, seated in an obligatory axial position, required for the generation of cytoplasmic replicons, is the source of travelling vectors (spermatozoa, lymphocytes ...) endowed with these potentially transforming nucleoproteins. 2) The centrifugally growing somatic tissues subjected to mitotic senescence. The progressive loss of replicons probably triggers meiotic-like recombinations and differentiation in distal tissues. The shedding of axial replicons to distal meiotic targets seems to be instrumental in transformation, initiating both, embryogenesis and cancer. This theoretical approach is applied to the histogenetic model of malignant melanoma of the skin. In this setting, the axial population is identified as lymphocytes involved in a process of extrathymic maturation (lichenoid lesions), in the same field where melanoma would arise. Pagetoid nests of melanocytes are considered to be the expression of TDUs evolving in a distal population of senescent neurocristic cells. This situation establishes the likelihood of mixing between potentially transforming lymphocytes and the meiotic melanocytes resulting in a transformed hybrid, the earliest cellular expression of malignant melanoma.

Synthetic retinoids inhibit the antigen presenting properties of epidermal cells in vitro

The clinical efficacy of retinoids in benign and malignant skin diseases involving immune mechanisms suggests that they affect the immunologic functions of the epidermis. However, these effects have yet to be demonstrated. The action of vitamin A (retinol) and the synthetic retinoids, isotretinoin, etretinate, acitretin, and arotinoid-free acid have been studied on the lymphocyte proliferation induced by phytohemagglutinin (PHA), by the mixed lymphocyte reaction (MLR), and the mixed epidermal cell-lymphocyte reaction (MECLR). The results for PHA-induced proliferations were highly variable for all the retinoids. However, in MECLR, the synthetic retinoids consistently reduced the proliferation by 20%-30%. This occurred at therapeutic drug concentrations of about 10(-7)M. In MLR, a minor decrease of 10%-15% was only found for higher concentrations (10(-5)M). Retinol induced no effect in either reaction. Further analysis of acitretin on MECLR showed that it reduced lymphocyte proliferation in a dose-dependent fashion. This reduction was combined with a decrease in cytotoxic T-lymphocyte induction (CTL). Addition of 10(-6)M acitretin at various times also revealed that its presence at cell culture initiation was necessary to inhibit proliferation significantly. Furthermore, cell treatments prior to MECLR showed that exposure of epidermal cells to acitretin was essential to produce this inhibition, suggesting that it acts directly on epidermal cells. Consequently, it is suggested that the specific inhibitory effect of synthetic retinoids on lymphocyte activation in MECLR may partly account for their therapeutic action on the skin.

Developmental biology of T cell receptors

T cell receptors are the antigen-recognizing elements found on the effector cells of the immune system. Two isotypes have been discovered, TCR-gamma delta and TCR-alpha beta, which appear in that order during ontogeny. The maturation of prothymocytes that colonize the thymic rudiment at defined gestational stages occurs principally within the thymus, although some evidence for extrathymic maturation also exists. The maturation process includes the rearrangement and expression of the T cell receptor genes. Determination of these mechanisms, the lineages of the cells, and the subsequent thymic selection that results in self-tolerance is the central problem in developmental immunology and is important for the understanding of autoimmune diseases.

A surface glycoprotein complex related to the adhesive receptors of the VLA family, shared by epidermal Langerhans cells and basal keratinocytes

A murine monoclonal antibody, designated K20, was raised by immunization with a human malignant T-cell line. It reacted specifically with membrane glycoprotein complexes on early haematopoietic cells, T cells, and monocytes. In epidermis, K20 specifically reacted with Langerhans cells and basal keratinocytes, as demonstrated by double labeling experiments. Membrane immunoprecipitation analysis demonstrated that the antigen identified by K20 on lymphoid cells and epidermal cells was different. While on lymphoid cells, K20 recognized glycoprotein complexes made of a constant 130-kD subunit associated with subunits of higher molecular weight ranging from 150 to 200 kD, a complex of 105-145 kD was precipitated from Langerhans and basal cells. Metabolic labeling studies demonstrated that these proteins were synthesized by the basal cells. The antigen identified by K20 was thought to belong to the integrins, a family of cell surface receptors that play a role in cell adhesion, cell interactions, wound healing, and immune defense mechanisms. K20 is the first monoclonal antibody that specifically recognizes a membrane antigen common to Langerhans and basal cells. Additionally, K20 is the first of five reported monoclonal antibodies to have been characterized on the epidermal cells that detect antigens shared by lymphoid subpopulations and normal basal keratinocytes.

Long-term efficacy, curative potential, and carcinogenicity of topical mechlorethamine chemotherapy in cutaneous T cell lymphoma

Complete responses lasting from 4 to 14 years were documented in 65 of 331 (20%) patients with cutaneous T cell lymphoma treated with topical mechlorethamine (HN2) between 1968 and 1982. Such long-lasting remissions occurred most often, but not invariably, in patients with patch or plaque phase mycosis fungoides without palpable lymphadenopathy (stage Ia or Ib). The likelihood of a continuous remission was enhanced by initiation of treatment before an unequivocal pathologic diagnosis. Despite the long-lasting responses in these patients, however, relapses have been documented in 11 (17%) of these patients, and all relapses occurred within 8 years of discontinuing maintenance topical chemotherapy. Thus, in our experience, a continuous remission lasting 8 or more years provides evidence that cutaneous T cell lymphoma can be eradicated by aggressive topical chemotherapy. This circumstance was observed in 35 patients, representing a cure rate of at least 11% overall. In addition, when compared with the general population of the United States, patients who received topical HN2 were at an 8.6-fold and a 1.8-fold increased risk for the development of squamous cell carcinoma and enhanced for Hodgkin's disease and colon cancer but not for systemic cancers known to be induced by systemic administration of alkylating drugs. These results compare favorably with experiences with topical HN2 chemotherapy at other centers but raise questions about the risks associated with long-term administration for maintenance of remissions.

Amino acid sequence of thymopoietin isolated from skin

The isolation of thymopoietin-reactive material in fetal bovine skin was monitored by means of a radioimmunoassay to thymopoietin. The amino acid sequence of this material was determined to be identical with that of thymopoietin isolated from the thymus. Experimental evidence suggests that thymopoietin in the circulation derives from the thymus and not from the skin, suggesting that the thymopoietin in keratinocytes has a local function, either apocrine and/or immunoregulatory.

Immunomodulation and Sézary syndrome: experience with thymopentin (TP-5)

The clinical, histological and immunological effects of long-term treatment with thymopentin (TP-5), administered 50 mg i.v. three times a week on alternate days, in four patients with Sézary syndrome is reported. In all four cases reduction of itching, oedema, scaling and thickening, and clearing of erythroderma were noted after 2 months treatment. Peripheral blood Sézary cells decreased in three cases. Reduction or suspension of the drug was followed by a clinical relapse. A loss of epidermotropism and a reduction in cell infiltrates were observed together with a dramatic reduction in epidermal and dermal Langerhans cells. An increase in the proliferative response to mitogens and in IFN-gamma production, and the expression of activation antigens in PHA stimulated cultures occurred after 3 months. HNK-I+ cells increased both in the peripheral blood and in the dermis following a transient increase in IL-2 receptors, suggesting that clinical response in TP-5 treated patients may be mediated by an increased production of IL-2 and consequent generation of cytotoxic cells or release of lymphokines able to augment NK activity.

An extract of bovine thymus stimulates human keratinocyte growth in vitro

An extract prepared from newborn calf thymus stimulated proliferation of human keratinocytes cultured from newborn foreskins and from skin biopsies of 26 adult volunteers aged 19 to 70 years. Growth over the 7-day assay period in the basal medium was age-dependent, with newborn cultures achieving a 10-fold increase in cell number over seeding density, old adult cultures barely maintaining their seeding density and young adult cultures intermediate in proliferative capacity. Maximally stimulatory extract concentration was 5-fold higher for newborn than for adult keratinocytes, with adult cultures experiencing toxicity at doses still growth-promoting for newborn cultures. At optimal extract concentration the maximal average increase in cell yield (66.3% for newborn, 53.6% for young adult, and 18.1% for old) indicated decreased mitogen responsiveness or increased inhibitor sensitivity with increasing donor age. Stimulation of cholera toxin-treated cultures was equally high, ranging from 39.4% to 145.9%, suggesting that the extract acts through a cyclic AMP-independent pathway. Thymic extract did not increase colony forming efficiency. Our findings provide further support for the concept of functional interactions between the skin and the immune system, in addition to the recognized morphologic similarities between thymic cells and keratinocytes. Furthermore, these data confirm earlier findings of an inverse relationship between mitogen responsiveness and donor age for cultured cells.

Role of epidermal Langerhans cells in viral infections

Langerhans cells function as highly potent antigen-presenting cells in the epidermis. In the last few years, their role in viral infections has been studied in various experimental systems. They have been shown to be involved in the pathogenesis of a number of infections of viral origin. These include vaccinia virus, human papilloma virus, herpes simplex virus, foot and mouth disease virus and human retrovirus infections. Studies on the effect of various factors, that are known to modulate the activity and density of Langerhans cell in the epidermis, may lead in the future to the development of new strategies aimed at inhibiting virus infections or even eradicating latent infection.

Induction of an immature T-cell phenotype in malignant helper T cells by cocultivation with epidermal cell cultures

The possible inductive effect of epidermal cells on T-cell maturation has been examined employing an in vitro cocultivation technique. Mononuclear cells from 6 patients with cutaneous T-cell lymphoma (CTCL) and from 12 healthy volunteers were studied. In the 6 CTCL patients, all showed an expansion of the helper T-cell subpopulation and in one patient with leukemic CTCL, there was almost complete replacement of peripheral blood mononuclear cells by malignant cells with a helper T-cell phenotype. Epidermal cells derived from normal human skin were cultured to confluent monolayers, and were cocultivated with the mononuclear cells from CTCL patients or normal controls for 48 h at a density of 10(6)/ml. Following cocultivation, the surface phenotype of the cells from the 12 healthy volunteers and 5 of the patients with CTCL showed no significant phenotypic change. In the patient with leukemic CTCL, however, the surface phenotype of the malignant T cells had changed, with the acquisition of the T6 antigen by the majority of the cells. Cells cocultivated in medium alone and with human fibroblast monolayers showed no change in surface phenotype. The malignant T cells from the leukemic CTCL patient failed to react in a mixed lymphocyte culture to lymphocytes from 2 different healthy donors, and showed no phenotypic change following culture with these lymphocytes, indicating that the phenotypic change seen was not due to allogeneic stimulation.

Human keratinocytes and epidermoid carcinoma cell lines produce a cytokine with interleukin 3-like activity

Keratinocytes are capable of releasing distinct immunomodulating cytokines such as epidermal cell-derived thymocyte activating factor (ETAF) and an epidermal cell-derived natural killer cell augmenting factor (ENKAF). The present study was performed to determine whether human keratinocytes also may secrete an interleukin 3 (IL-3)-like mediator and thereby participate in the regulation of mast cell activity in the skin. Supernatants of freshly isolated human epidermal cells (EC) and malignant keratinocyte cell lines (A 431, SCC) were tested for their capacity to induce the proliferation of IL-3-dependent cell lines 32 DCL and FDCP. Human epidermal cell interleukin 3 (EC IL-3) is spontaneously released by freshly isolated EC, A 431, and squamous cell carcinoma (SCC) cells. However, both normal EC and A 431 cells produced increased levels of EC IL-3 activity when cultured in the presence of different stimulants, such as phorbol myristate acetate and lipopolysaccharide. The EC IL-3 activity was not inhibited when treated with a monoclonal anti-IL-1 or anti-IL-2-antibody. Biochemical characterization showed that human EC IL-3 has a molecular weight of 17K, elutes of DEAE-ion exchange high-performance liquid chromatography (HPLC) as one major peak at 0.36 M NaCl, and upon HPLC-chromatofocusing exhibits 3 isoelectric points of 7.8, 7.5, and 5.6. Upon reversed-phase HPLC, EC IL-3 activity eluted at about 100% acetonitrile. When highly purified EC IL-3 was labeled with 125I and subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis, a single homogeneous band exhibiting a molecular weight of 17K was seen, which correlated with the IL-3 activity and was free of ETAF/IL-1, IL-2, and interferon activity. These data indicate that human EC synthesize an IL-3-like cytokine which is distinct from ETAF/IL-1, IL-2, and interferon and thereby may participate in the regulation of mast cell activity during inflammatory and fibrotic, as well as hypersensitivity reactions.

Epidermal cell-derived lymphocyte differentiating factor (ELDIF) inhibits in vitro lymphoproliferative responses and interleukin 2 production

We have examined the biologic characteristics and immunologic properties of epidermal cell-derived lymphocyte differentiating factor (ELDIF), a lymphocyte differentiating factor produced by cultured human keratinocytes. The ELDIF was semipurified by a gel filtration procedure. This factor, which is distinct from prostaglandins, epidermal cell-derived thymocyte activating factor (ETAF), and the well-known thymic hormones (thymulin, thymopoietin, and thymosin alpha 1) did not exhibit any interleukin (IL)-1, IL-2, or IL-3 activity. It strongly inhibited in vitro lymphoproliferative responses of normal mouse spleen cells to phytohemagglutinin, concanavalin A, and lipopolysaccharide. This dose-dependent phenomenon was associated with a suppression of IL-2 production rather than any toxic effect. It can be concluded that ELDIF, a product of human epidermal cells, which displays in vitro T-cell differentiation and regulatory activities, could be of major importance in vivo in the control of cutaneous inflammatory reactions.

Human keratinocyte-lymphocyte reactions in vitro

To extend our observation that recombinant gamma interferon (r-IFN-gamma) induces the synthesis and expression of HLA-DR antigen we have investigated 2 major areas including the modulation of r-IFN-gamma-induced HLA-DR expression and the possible immunologic consequences of keratinocyte HLA-DR expression in vitro. The induction of keratinocyte HLA-DR expression was greater for continuous compared with pulse dosage (0.5-24 h) of r-IFN-gamma and was markedly decreased after trypsinization of attached monolayers into single cell suspensions. The r-IFN-gamma caused induction of HLA-DR and this was not influenced by either pretreatment with irradiation, PGE2, or indomethacin. Both HLA-DR+ and HLA-DR- cultured keratinocytes induced RNA synthesis and gamma interferon production by allogeneic peripheral blood mononuclear leukocytes (PBMLs) indicating mononuclear cell activation. However, this activation was not followed by significant mitogenesis and only slightly increased levels of [3H]thymidine incorporation (maximal = 5800 cpm) by the PBMLs was observed. Cultured keratinocytes apparently inhibit both lectin-driven and mixed-lymphocyte reactions by producing a soluble mediator which is not dialyzable, or inhibited by pretreatment with indomethacin or anti-alpha, -beta, -gamma interferon antibodies. These results suggest that lymphocyte-keratinocyte reactions in vitro are complex and may be mediated by a variety of cytokines, lymphokines, and prostaglandins.

The skin immune system Its cellular constituents and their interactions

The term immunodermatology describes the systematic investigation of the complex mechanisms of the 'skin immune system' in health and disease. In this review Jan Bos and Martien Kapsenberg discuss the skin's vascular and lymphatic systems and the various cells which participate in the immune response. These include Langerhans' cells, indeterminate cells, veiled cells, endothelial cells, mast cells, tissue macrophages and 'homing' T lymphocytes, which are all present in skin under physiological conditions.

Keratinocyte-derived T-cell growth factor: a T-cell growth factor functionally distinct from interleukin 2

T-cell growth factor, more recently termed interleukin 2 (IL-2), is the product of activated T lymphocytes and is considered the principal trophic factor for T lymphocytes. The activity of IL-2 preparations is assessed by the degree to which they support the growth of various IL-2-dependent cell lines. We report that murine epidermal epithelial cells (keratinocytes) produce and release a factor that supports the growth of the helper-T-cell-derived, IL-2-dependent cell line HT-2. This substance, keratinocyte-derived T-cell growth factor (KTGF), does not support the growth of an IL-2-dependent cell line derived from cytotoxic T cells (line CTLL-2). This differential effect on IL-2-dependent cell lines is unique to KTGF. KTGF has an apparent molecular weight of 25,000-35,000 and has properties similar to those of conventional IL-2 by reversed-phase and gel-filtration HPLC analysis. However, even highly purified KTGF fails to stimulate the proliferation of CTLL-2 cells. The observation that epidermal epithelium produces a trophic factor for T lymphocytes may help explain the basis for preferential proliferation of T cells in the microenvironment of skin in certain dermatologic disorders. Further, it suggests that different IL-2-dependent T-cell lines may have distinct growth requirements and that non-lymphocyte cell types may produce factors capable of maintaining the growth of T cells.

Reactivity of T lymphotropic retrovirus antibody (12/1-2) in man: comparison of epidermis with other epithelial cells

The reactivity of a monoclonal antibody against human T lymphotropic retrovirus (antibody 12/1-2, recognising the HTLV-1 p19 internal core viral protein) with benign and malignant cutaneous biopsy specimens was examined and compared with results obtained on normal skin, on various other human cells and tissues, and on immunoblotted extracts of tonsil squamous epithelium. In keeping with previous studies, 12/1-2 labelled a proportion of the thymic epithelial stroma and the entire layer of basal cells in stratified non-keratinized and keratinized epithelium. Furthermore, antibody 12/1-2 reacted with basal cell carcinomas and showed an essentially identical staining pattern in normal skin, cutaneous T cell lymphomas, and a range of benign dermatoses. The dot blot preparations showed that 12/1-2 recognised an antigen associated with keratin intermediate filaments. These data indicate that antibody 12/1-2 forms a useful marker for subsets of epithelial cells, which presumably participate in T cell education, and that a range of cutaneous disorders of widely different aetiology show no abnormalities in epithelial expression of this antigen.

Evolution of a terminal deoxynucleotidyl transferase-positive lymphoma from a chronic T cell lymphocytosis

A 56-yr-old Caucasian man presented with a generalised scaly rash and a peripheral blood lymphocytosis of 5.6 X 10(9)/l. 5 yr later he developed cutaneous nodules, lymphadenopathy and hepatosplenomegaly. Cells with convoluted nuclei and prominent nucleoli were seen in the peripheral blood. He underwent splenectomy and received intensive chemotherapy but died 6 months later with CNS infiltration. At presentation the peripheral blood lymphocytes were E-ve, UCHT1 + ve, and OKT8 + ve. Following transformation, cells in blood, spleen and CSF were E-ve, OKT11 + ve, DR + ve and Tdt + ve. A proportion of these cells had a Sézary-like appearance at E/M. The splenic cells showed functional suppressor activity. This is the first reported case of the evolution of a Tdt + ve lymphoma from a post-thymic T cell lymphocytosis.

Advances in the immunobiology of the skin. Implications for cutaneous malignancies

Recent advances in cutaneous immunobiology have led to the realization that skin is an important and unique immunologic organ. Studies on the immunobiology of skin cancers induced by ultraviolet radiation indicate that immune mechanisms can play a crucial role in the development of cutaneous tumors. This paper summarizes the evidence linking skin and the immune system and discusses current hypotheses concerning the mechanisms by which UV radiation interferes with cutaneous immunity. The significance of these findings for cutaneous carcinogenesis is discussed.

Pattern of distribution of T lymphocytes, Langerhans cells and HLA-DR bearing cells in normal human oral mucosa

The tissue distribution of helper/inducer and suppressor/cytotoxic T cells, Langerhans cells (LC) and HLA-DR bearing cells was determined in normal oral mucosa by use of monoclonal antibodies OKT4, OKT8, OKT6 and OKIa1, respectively. OKT4+ and OKT8+ cells were invariably present in normal oral epithelium and in the lamina propria. OKT8+ cells were consistently seen inside the basal cell layer of the epithelium. The distribution of LC in oral epithelium showed regional variation. In palatal epithelium LC were evenly distributed in the basal half of the epithelium, whereas in buccal mucosa the highest concentration of LC was seen in the epithelium overlying the tips of connective tissue papillae. OKIa1 stained dendritic cells in the epithelium and plump cells with small dendritic processes in the connective tissue. Some of the latter were located close to the basal cells of the epithelium. The consistent relationship between immunocompetent cells and the epithelium of the oral mucosa suggests the presence of a local immunologic defence barrier in the oral mucosa.

Origin and function of Thy-1+ dendritic epidermal cells in mice

The epidermis of normal mouse skin incorporates a newly-recognized population of dendritic cells which express relatively large amounts of the cell surface glycoprotein, Thy-1 antigen. These cells, termed Thy-1+dEC, are distinct from both epidermal Langerhans cells (LC) and melanocytes, and they populate cutaneous sites in surface densities which range to as high as 580 cells/mm2, approximately two-thirds that of LC. Studies of lethally irradiated mice which were reconstituted with semiallogeneic bone marrow cells and mice which received grafts of semiallogeneic skin have demonstrated that some, if not all, Thy-1+dEC are of bone marrow origin, and that they are capable of migrating into epidermis from a vascular source. Thy-1+dEC expressed both asialo GM1 and a cell surface determinant recognized by the monoclonal antibody 20-10-5S, further suggesting their functions will be included among those normally ascribed to lymphoreticular cells. Isolation of epidermal cells with the Fluorescence Activated Cell Sorter (FACS) was successful in producing relatively pure populations of Thy-1+dEC and LC. Such technological advances as this should facilitate testing several hypotheses concerning the ultimate function of these cells, including the possibilities that they are antigen-presenting cells which selectively activate down-regulating signals, T lymphocytes, natural killer (NK) cells, or natural suppressor (NS) cells.

A membrane protein preferentially expressed by a subpopulation of immature lymphoid cells, epidermal basal keratinocytes, and other epithelial cells

A murine monoclonal antibody, designated EL-1, was raised by immunization with a human malignant T cell line. It reacted specifically with a membrane antigen expressed on T and B lymphoblastoid cell lines, a subpopulation of normal thymocytes and bone marrow lymphocytes, lymphocytes from a subset of patients with non-B, non-T cell acute lymphoblastic leukemia or T cell acute lymphoblastic leukemia and epithelial stem cells. The latter reactivity was especially striking in the skin, where only basal epidermal keratinocytes and epidermal appendages, including eccrine sweat glands, sebaceous glands and hair follicles, stained positively. A human epidermoid carcinoma cell line was also stained by EL-1. Suprabasilar keratinocytes and acellular keratin did not stain. However, in vitro proliferating fetal lung fibroblasts stained positively. Membrane immunoprecipitation analysis demonstrated that the antigen recognized by antibody EL-1 is a single protein of molecular weight 105 kilodaltons which did not change with exhaustive chemical reduction. Metabolic radiolabeling studies demonstrated that this protein is synthesized by the cell and not merely taken up from the culture medium. This antibody can be useful in studying keratinocyte differentiation in epidermal malignancies and normal skin.

Expression of antigens by cultured epithelial cells: comparison of epidermis and thymic epithelium

We have established long term in vitro cultures of human thymic epithelium and human epidermis free of contaminating fibroblasts. The cultured cells were examined using a panel of monoclonal antibodies which were raised against human thymic stroma and recognize tissue specific differentiation antigens of human epidermis and thymic epithelium. A subset of cultured epidermal cells (50%) and thymic epithelial cells (18%) expressed the TE-4 antigen characteristic of basal keratinocytes in skin and endocrine epithelium found in the subcapsular cortex and medulla of the thymus. Subpopulations of the cultured cells expressed the antigens detected by antibodies TE-8 and TE-15. In tissue sections antibodies TE-8 and TE-15 bound to the stratum granulosum and stratum corneum of skin and to the Hassall's bodies of thymus, and therefore recognize antigens characteristic of late stages of keratinized epithelial differentiation. In addition, a subset of thymic epithelial cells expressed the antigen detected by antibody TE-3 which is expressed by nonendocrine thymic epithelium found in the thymic cortex. Thus, in vitro cultures of both epidermal and thymic epithelial cells expressed the entire array of differentiation antigens detected by our panel of monoclonal antibodies. This approach can be used to evaluate the role of components of the thymic microenvironment at various stages of differentiation on developing T lymphocytes. In addition, the cultured epidermal cells can be used to evaluate epidermis as a site of extrathymic T cell maturation.