Human epidermal Langerhans cells and peripheral blood monocytes. Accessory cell function, autoactivating and alloactivating capacity and ETAF/IL-1 production

By IL-1 signaling, monocyte-derived cells dramatically enhance the epidermal antimicrobial response to lipopolysaccharide

Epithelia react to microbial pathogens by mounting a defensive response that includes the production of antimicrobial peptides. In this study, we show that, in human epidermal cultures, Escherichia coli LPS was a very weak direct inducer of human beta-defensin (HBD)-2 mRNA and peptide, but the induction was greatly amplified when monocyte-derived cells (MoDeC) acted as intermediaries between LPS and the epidermis. IL-1R antagonist largely reversed the effect of MoDeC on epidermal HBD-2, indicating that, from among the many products of MoDeC, IL-1 was the dominant inducer of HBD-2 synthesis. In normal fresh human skin, which contains Langerhans cells and other myeloid cell types, in addition to keratinocytes, LPS also induced HBD-2 in an IL-1-dependent manner. In DNA microarray expression studies, HBD-2 was one of the most abundant mRNAs induced in epidermis by LPS-treated MoDeC, and its induction was reversed by IL-1Ra. Thus, epidermal response to LPS is potently amplified by MoDeC through IL-1-mediated signaling, leading to a selective increase in the synthesis of the antimicrobial peptide HBD-2. This pattern of responses establishes a key role for both IL-1 and HBD-2 in the host defense reaction of the epidermis.

Dynamic nature and function of epidermal Langerhans cells in vivo and in vitro: a review, with emphasis on human Langerhans cells

Epidermal Langerhans cells (LC) are Birbeck granule-containing bone-marrow-derived cells, which are located mainly in the suprabasal layer of the epidermis. They can be readily identified by their strong expression of CD1a and MHC class II molecules. In addition to these 'classical' properties, an extensive phenotypic profile of normal human LC, summarized in this review, is now available. The powerful capacity of LC to activate T lymphocytes is clearly documented and, to date, LC are recognized as the prominent antigen-presenting cells of the skin immune system. They are generally believed to pick up antigens encountered in the epidermis and to migrate subsequently from the epidermis to the skin-draining lymph nodes. Upon arrival in the paracortex of lymph nodes, the antigen-laden LC transform into interdigitating cells and they present antigen to naive T lymphocytes in a MHC class II-restricted fashion; this results in the generation of antigen-specific immune responses. It has also been demonstrated that transformation of LC into interdigitating cells occurs when LC are cultured in vitro. Both in vivo and in vitro studies have indicated that properties of LC, such as phenotype, morphology and the stimulatory potential to activate T lymphocytes, are dependent on the local microenvironment in which the LC reside. The essential role of LC in the induction of contact allergic skin reactions and skin transplant rejection is well established.

Lymphocyte proliferation test as a diagnostic aid in chromium contact sensitivity

We investigated the clinical applicability of the lymphocyte proliferation test (LPT) in chromium contact sensitivity. 6 out of 8 chromium-sensitive patients were positive in the LPT, whereas none of 8 non-chromium-sensitive controls responded in vitro to tri- or hexavalent chromium compounds. LPT thus appeared to offer an additional diagnostic tool in chromium sensitivity. We also studied cellular interactions in 4 of our chromium-sensitive patients. Sensitized T-lymphocytes could be activated to proliferate only in the presence of accessory cells, of which epidermal Langerhans cells (LC) appeared more efficient than blood adherent cells.

Langerhans cells but not monocytes are capable of antigen presentation in vitro in corticosteroid contact hypersensitivity

Corticosteroids suppress delayed-type hypersensitivity (DTH) reactions in vivo and impair lymphoid cell functions in vitro. In contact hypersensitivity (CHS) to corticosteroids, however, the corticosteroids are capable of inducing DTH responses in vivo. The present study examined the capacity of corticosteroids to induce in vitro proliferation of T lymphocytes from patients with CHS to corticosteroids. With peripheral blood mononuclear adherent cells as antigen-presenting cells (APC) and hydrocortisone-17-butyrate (H-17-B) as hapten, no proliferation responses were detected of T lymphocytes from patients with CHS to H-17-B. However, when epidermal Langerhans cells (LC) were used as APC, weak proliferation responses were observed.

The Langerhans cell: an underestimated cell in atopic disease

Langerhans cells (LC) are very potent antigen-presenting cells. In atopic disorders such as allergic rhinitis and atopic dermatitis LC are known to bear IgE surface molecules. IgE-positive LC can bind allergen and present it to T lymphocytes to induce an allergen-specific T-cell response and IgE synthesis. Therefore, IgE-bearing LC might play an important role in the triggering of the immune system to maintain ongoing IgE synthesis. The importance of the IgE-bearing LC in atopy has not been assessed but deserves further investigation to find out more about the part played by these cells, not only in the atopic disorders described here but also in others such as gastrointestinal allergy and allergic asthma.

Osteomyelitis-like bone lesions in acne fulminans

Two young males with acne fulminans (AF) are described. In addition to severe skin lesions, they had musculoskeletal symptoms including bacteriologically negative osteolytic lesions in the clavicles. Both patients received antibiotics for suspected septic infections. The response was unsatisfactory in both patients, and combination treatment with prednisolone was started. A favourable response was observed, and a relapse occurring in the first patient was controlled by steroids alone. The possible pathomechanism of bone lesions in AF is discussed.

Immediate decrease in antigen-presenting function and delayed enhancement of interleukin-1 production in human epidermal cells after in vivo UVB irradiation

Human skin was irradiated in vivo with a single UVB dose (100 mJ/cm2 or 200 mJ/cm2) to examine simultaneously the antigen-presenting function and interleukin-1 (IL-1) production capacity of irradiated epidermal cells (EC). Suction blisters were produced on irradiated areas on days 0, 3 and 7 after UVB. Irradiated EC were harvested and co-cultured with autologous T lymphocytes in the presence of antigens (PPD, HSV) or mitogen (ConA). Culture supernatants were tested for IL-1 activity using the thymocyte comitogenity assay. We found that a single 200 mJ/cm2 dose of UVB caused an immediate suppression of the antigen-presenting function of EC, but no alteration in their IL-1 production capacity or surface marker expression (ATPase, CDI). PPD- and HSV-induced lymphocyte proliferation was decreased 70-80% and ConA-driven proliferation 30% when compared to non-irradiated EC. However, this suppression was restored on days 3 and 7 after UVB irradiation, this being coexistent with an increased capacity of EC to produce IL-1. It remains to be elucidated whether the immediate UVB-induced photoimmunosuppression observed in the present study is due to inhibitory mediators or impaired membrane function of EC or both.

Basophil histamine release and lymphocyte proliferation tests in latex contact urticaria. In vitro tests in latex contact urticaria

Basophil histamine release and lymphocyte proliferation tests were examined with latex allergen prepared from surgical gloves in 15 patients with latex contact urticaria. The basophil histamine release test (BHRT) yielded positive results in 13/14 (93%) patients, whereas commercial latex RAST was positive in only 9/15 (60%) patients. Lymphocyte proliferation test (LPT) was positive in 3/15 (20%) patients, suggesting that cell-mediated immune reactions may also occur in latex allergy. However, patch tests to latex were negative and neither were epidermal Langerhans cells able to present latex antigen to T lymphocytes in vitro.

Epidermis and lymphocyte interactions during an allergic patch test reaction. Increased activity of ETAF/IL-1, epidermal derived lymphocyte chemotactic factor and mixed skin lymphocyte reactivity in persons with type IV allergy

Recently, we have found an increased activity of epidermal-derived thymocyte-activating factor (ETAF/IL-1) and epidermal lymphocyte chemotactic factor (ELCF) in epidermis overlying a positive tuberculin skin reaction. In the present study, we investigated 20 patients with confirmed or suspected allergic contact dermatitis by using the suction blister technique before and during patch testing. The ETAF/IL-1 was found in epidermis before patch testing. Its presence increased 2.8-fold in epidermis overlying a positive patch test compared with pretesting values. This increase was statistically significant. Interestingly, nontested skin also showed a significant increase of ETAF/IL-1, which was 1.9-fold higher than pretest values. The ETAF/IL-1 activity in patch test areas was significantly correlated with the clinical response. ELCF is not present in epidermis from noneczematous persons. We observed a significant content of ELCF in three of seven patients with eczema prior to patch testing. After patch testing, all patients showed ELCF in epidermis. Nontested skin showed a 1.5-fold higher content of ELCF compared with pretest values, and in the test area ELCF was 1.8-fold higher. The increases were statistically significant. We performed mixed skin lymphocyte reactions in seven patients using epidermal cells from the patch test area. All patients with a positive patch test had an increased mixed skin lymphocyte reactivity compared with epidermis coming from a negative reaction.

Immunostimulatory capabilities of highly enriched Langerhans cells in vitro

Langerhans cells (LC) are epidermal antigen-presenting cells capable of inducing allogenic, antigen-specific, and cytotoxic T cell proliferation. Previous studies have examined the dynamics of LC maintained in vitro in crude epidermal cell (EC) suspensions in which the major cell type is the keratinocyte (KC). To avoid the confounding effects of KC and other immunoregulatory cells on LC dynamics in vitro, highly enriched murine LC (85%) were studied, through 72 h of incubation in vitro, for their ability to present alloantigen (in a primary allogenic proliferation assay) and foreign antigen (in a secondary autologous proliferation assay). The results were compared to similar studies using crude EC suspensions. Freshly prepared LC are very poor stimulators of a primary allogenic proliferation response, with a 12- to 16-fold increase in stimulatory capacity by 72 h using panned-enriched and crude EC suspensions, respectively. Similarly, freshly prepared LC are weak stimulators of a secondary autologous proliferation response, with a 2.5- to 6-fold increase in immunostimulatory capability by 72 h. The overall increased stimulatory effect observed with the crude EC suspensions compared to highly enriched LC is most likely attributed to the effect of KC on T cell proliferation, rather than to a maturation effect of KC on LC during the 72 h of in vitro incubation. Using back-scattered electron imaging, the surface density of MHC-class II molecules (Ia) increased three- to fourfold through culture, which parallels the increase in functional ability. This study demonstrates that LC in either a crude or highly enriched cell suspension mature into potent immunostimulatory cells after incubation in vitro with an increased surface expression of Ia molecules. Keratinocytes are not necessary for LC maturation in vitro, but seem to exert some stimulatory effect by enhancing lymphocyte proliferation in the functional assay system.

Langerhans cell- and T-lymphocyte functions in patients with atopic dermatitis with disseminated cutaneous herpes simplex virus infection

We studied whether Langerhans cell (LC)- and T-lymphocyte functions of atopic dermatitis (AD) patients are impaired. Our study groups consisted of 6 patients with AD with previous disseminated herpes simplex virus infection (AD + HSV), 8 patients with ordinary AD, and 5 healthy subjects. Suction blisters were performed on abdominal skin and LC isolated on the basis of their attachment to IgG-coated erythrocyte monolayers. Antigen-presenting function of purified LC was studied by measuring the proliferation of HSV-stimulated T cells. Langerhans cells were also used to stimulate T cells in autologous mixed cell reaction (AMCR). In addition, the production of epidermal cell thymocyte-activating factor (ETAF) by crude epidermal cells was measured. The HSV-induced T-cell proliferation in AD + HSV and AD patients was comparable with that of controls. The AMCR responses of patients with AD + HSV and AD were clearly diminished when compared with healthy controls. Patients with AD also produced significantly less ETAF than controls. Our results suggest that HSV antigen-presenting function of LC from patients with AD + HSV seems to be intact. Defective AMCR may reflect an abnormality in autoregulation and generation of effector cells and this together with decreased ETAF production may have pathogenetic significance in AD.