Removal of Langerhans cells from human epidermal cell suspensions by immunomagnetic particles

CD1a and CD1c cell sorting yields a homogeneous population of immature human Langerhans cells

There is increasing evidence that ex vivo generated Langerhans cells (LCs) cannot fully substitute for their physiological counterparts in normal epidermis when studying the immunobiology of this prototype of a tissue-residing immature dendritic cell (DC). Here, we present CD1-based magnetic-activated cell-sorting (MACS) protocols for the effective isolation of human epidermal LCs. CD1c selection yielded a homogeneous population of pure and viable HLA-DR(+)/CD1a(+) DCs, with the ultrastructural features, surface antigen expression and cytokine profile, characteristic of epidermis-resident immature LCs. The immature state and functional integrity were established by allogeneic mixed lymphocyte reactions showing a weak stimulatory capacity of freshly isolated cells and upregulation upon stimulation. Characterizing the cells in more detail, we could demonstrate for the first time that normal human LCs express CXCR4, CD40 ligand (CD40L), and Fas and Fas ligand (FasL). The observed constitutive transcription of TGF-beta suggests that the viability and immature state of epidermal LCs are maintained not only by the TGF-beta production from the microenvironment, but also in an autocrine or paracrine manner. LPS and IFN-omega stimulated the expression of the inflammatory cytokines TNF-alpha and IL-1beta, and there was secretion of IL-12p70 after CD40 ligation. Remarkably, the CD1-sorted LCs showed no loss of their Birbeck granules and CD1a expression upon culturing and no spontaneous phenotypic and functional maturation into potent antigen-presenting cells (APCs). We conclude that human epidermal LCs obtained by the CD1c cell-sorting protocol are optimal candidates with which to elucidate the properties and capabilities of immature cells and to develop immunotherapeutic vaccines.

Adhesion molecules and IL-1 costimulate T lymphocytes in the autologous MECLR in psoriasis

Membrane molecules such as CD36 (OKM5), intercellular adhesion molecule-1 (ICAM-1, CD54), gamma interferon-induced protein 10 (gamma-IP10) and IL-1 are induced and/or upregulated in psoriatic epidermis. These molecules have important accessory, trafficking or signalling functions in the immune system and also play a role in the pathophysiology of psoriasis. The relevance of adhesion molecules, CD36 and epidermal IL-1 in psoriasis was studied in vitro in the autologous mixed epidermal cell - T lymphocyte reaction (MECLR). Their level of expression was quantitated in epidermal cell suspensions (ECS) from patients with psoriasis and their function was assessed by blocking with specific mAbs and antisera or by depleting CD36+ cells from the ECS prior to the MECLR. ECS from psoriatic lesions contained increased numbers of CD36+ (23 +/- 12%), ICAM-1(+) (31 +/- 14%) and IL-1(+) (57 +/- 21%) cells. The autologous MECLR was inhibited in samples from all patients by mAb to CD2 (LFA-2), CD11a (LFA-1alpha), CD18 (LFA-1beta), ICAM-1, CD58 (LFA-3) and an antiserum to IL-1beta. Thus, adhesion molecules facilitate inflammation in psoriasis not only via adhesion and recruitment of T lymphocyte in psoriatic lesions, but also via activation of T cells. Furthermore CD36 molecules on psoriatic epidermal cells do not costimulate autologous T lymphocytes in psoriasis. The observed costimulatory function of IL-1beta in the MECLR emphasizes its relevance in psoriasis.

Enhanced production of biologically active interleukin-1 alpha and interleukin-1 beta by psoriatic epidermal cells ex vivo: evidence of increased cytosolic interleukin-1 beta levels and facilitated interleukin-1 release

The expression of interleukin (IL)-1 is altered in psoriatic lesions. However, little is known about the actual production of IL-1 alpha and IL-1 beta by psoriatic epidermal cells (EC). We monitored IL-1 in the extracellular, the membrane and the intracellular compartment of freshly isolated EC from untreated lesional psoriatic (PP) and normal healthy (NN) skin during non-stimulated short-term cultures, representing a psoriasis model ex vivo. Cytokines were measured using bioassays combined with neutralizing antibodies and enzyme-linked immunosorbent assay in parallel. PP EC released significantly increased amounts of biologically active IL-1 alpha and IL-1 beta in a ratio of 3:1, whereas NN EC only released IL-1 alpha. Also, the release of IL-6, but not of TNF-alpha, by PP EC was significantly increased. Membrane-associated IL-1 activity, analyzed using glutaraldehyde-fixed EC, was low and not unique to PP EC. The cytosol of PP EC contained significantly increased levels of immunoreactive IL-1 beta. Furthermore, PP EC displayed loss of membrane integrity, as determined by trypan blue exclusion and release of cytosolic lactate dehydrogenase. This facilitated release of intracellular IL-1. Depletion of CD45+ cells showed that intraepidermal leukocytes did not contribute to the production of IL-1. Our observations show that resident PP EC express enhanced IL-1 production ex vivo, which is due to an increased cytosolic IL-1 beta content and facilitated IL-1 release. This study provides the first evidence that PP EC can produce bioactive IL-1 beta.

Rapid purification of human Langerhans cells using paramagnetic microbeads

Detailed studies on the biology of Langerhans cells (LC), which account for only 1-3% of all epidermal cells, require isolation from their cutaneous symbionts. Several techniques of LC isolation have been reported, including positive enrichment with mAb coupled to immunomagnetic beads. The disadvantage of this technique is the size of the beads (approximately 2-5 microns), which can interfere with subsequent phenotypic and functional analyses. This limitation prompted us to test whether paramagnetic microbeads (15 nm) employed by the MACS system could be used to purify LC from human skin. To isolate fresh LC (fLC), epidermal cell suspensions (EC) were stained with anti-CD1a mAb and with appropriate secondary reagents conjugated to microbeads and to FITC. They were then passed over a separation column and exposed to a strong magnetic field. Thereafter both CD1a-depleted and CD1a-enriched cells were collected. Cultured LC (cLC) were isolated by staining 72-h cultured EC with anti-HLA-DR mAb followed by the same isolation procedure. Using this technique, we could routinely isolate viable EC that were 45-88% CD1a+ or HLA-DR+ as determined by FACS. Two-color FACS analysis demonstrated the majority of MACS-purified cells to be CD1a+/HLA-DR+, indicating that they were indeed LC. By transmission electron microscopy (TEM), the MACS-purified CD1a+/HLA-DR+ cells showed typical ultrastructural characteristics of LC. Furthermore, MACS-purified fLC or cLC were functionally intact, because they stimulated the proliferation of alloreactive T cells in a primary, one-way, mixed epidermal cell leukocyte reaction (MECLR). We conclude that MACS-separation is an efficient and rapid method to isolate human fLC and cLC of high purity and unimpaired function.

Antigen presenting capacity of Langerhans cells from rat oral epithelium

The ability of Langerhans cells (LC) from rat oral mucosa to internalize and process antigens and to participate in the induction of T cell mitogenesis was examined. To purify LC from epithelial cells, monoclonal anti-class II antibodies and immunomagnetic beads were employed. Suspensions of epithelial cells, containing LC, were found to be effective in mediating a Con A-induced T cell proliferation. Depletion of class II molecule-expressing LC reduced the proliferation of T cells by 80%. Presentation of ovalbumin (OA) to primed T cells was found to be dependent on the concentration of OA and the number of LC. Partially purified LC were five times as effective in inducing proliferation of primed T cells as the untreated suspension of epithelial cells. The data suggest that LC obtained from rat oral mucosa can generate accessory signals, process antigens and serve as antigen-presenting cells.

Antigen-presenting capacity in normal human dermis is mainly subserved by CD1a+ cells

A proposed role for antigen-presenting dermal dendrocytes in the pathogenesis of many dermal inflammatory skin diseases remains speculative. We therefore sought to determine the phenotype and functional characteristics of antigen-presenting cells isolated from normal human dermis. Normal adult human skin was incubated overnight with dispase at 4 degrees C, the epidermis was removed, and the residual dermal preparation was then minced and digested with a mixture of hyaluronidase, collagenase, and DNAase at 37 degrees C, prior to filtration through mesh. Dermal cell suspensions thus obtained were stained using specific monoclonal antibodies, and analysed by fluorescence microscopy or flow cytometry. Mean values were as follows: CD45+ leucocytes 39%, HLA-DR+ cells 39%, Ulex europaeus agglutinin I+ endothelial cells 26%, CD1a+ cells 3.9%, CD11b+ cells 16%, CD11c+ cells 6%. Mitomycin C-treated crude dermal cell suspensions induced allostimulation of peripheral blood mononuclear cells in a 7-day culture, as assessed by 3H-TdR incorporation. Depletion of CD1a+ Langerhans-like cells from the dermal cell preparation, by 95, 74 and 90% in three separate experiments using immunomagnetic beads, reduced 3H-TdR incorporation at optimal responder-to-stimulator cell ratios by 90, 64, and 87%, respectively. Our findings suggest that, in normal human dermis, the great majority of the alloantigen-presenting capacity resides in the CD1a+ Langerhans cell-like dendritic antigen-presenting cell population, and not to any great extent in either CD1a- macrophage-like cells, or HLA-DR+ endothelial cells. The relationship of the CD1a+ dermal antigen-presenting cells to the Langerhans cell lineage remains to be determined.

Immunomagnetic separation as a final purification step of liver endothelial cells

We describe a fast and reproducible method that can be used as a final step in obtaining pure populations of liver endothelial cells. This method employs endothelial cell specific lectin covalently bound to magnetic polystyrene beads (Dynabeads). Evonymus europaeus agglutinin (EEA)-coated Dynabeads were used to purify monkey liver endothelium from Percoll gradient separated nonparenchymal cells. EEA-coated beads were also successfully used to purify monkey aortic endothelial cells. The endothelial cells grew to confluence as a cobblestonelike monolayer, expressed Factor VIII related antigen, and incorporated acetylated-low density lipoprotein. The magnetic beads seemed not to modify the normal properties of the isolated endothelium, thus facilitating their use in experimental studies. This immunomagnetic separation technique may be applicable for purification of endothelial cells from a wide variety of tissue sources.

Purified human oral mucosal Langerhans cells function as accessory cells in vitro

Oral mucosal Langerhans cells (OMLC) may have an important role in the induction of immune responses to oral pathogens. In this study, anti-HLA-DR antibody-coated immunomagnetic beads were used to purify OMLC from suspensions of normal human buccal epithelium and the capacity of the purified cells to function as accessory cells (AC) was investigated. Electron microscopy was used to show that the purified cells possessed all recognized ultrastructural features previously described in epidermal Langerhans cells. Using T lymphocyte proliferation assays in hanging drop microcultures, it was found that purified OMLC could function as AC for responses to concanavalin A by autologous T cells. Purification of OMLC from small biopsies of oral mucosa has enabled us to show that OMLC, like epidermal Langerhans cells, can function as AC in vitro.

Fc gamma RII/CD32-negative human Langerhans cells may be responsible for the immunostimulatory activity of freshly isolated epidermal cells

Cultured murine and human epidermal Langerhans cells (LC) undergo a phenotypical and functional maturation process. In fact, they loose Fc gamma RII and Birbeck granules, increase HLA-DR expression, and become potent accessory cells for allogeneic MLR. However, resident/freshly isolated human epidermal LC represent a phenotypically heterogeneous cell population. Indeed, a subset of CD1a+ LC lacks Birbeck granules, is Fc gamma RII/CD32-, and strongly expresses HLA-DR and the RFD1 antigen that is considered to be specific for interdigitating cells. In the present study the functional capacity of this Fc gamma RII/CD32- CD1a+ LC subset was investigated in MLR assays by comparing the stimulatory activity of freshly isolated crude epidermal cells (EC) with that of freshly isolated EC depleted in CD1a+ or in Fc gamma RII+ cells. Thereby, we observed that crude EC stimulated allogeneic PBMC while the removal of CD1a+ cells abrogated this stimulation. However, crude EC depleted in Fc gamma RII/CD32+ cells still exhibited a stimulatory capacity that was at least equal to that of crude EC. Taken together, these data suggest that among resident human epidermal LC there exists a subset of phenotypically and functionally more differentiated cells that may be solely responsible for the stimulatory capacity of freshly isolated crude EC.

Effects of epidermal Langerhans cell's conditioned medium on keratinocytes: a role of Langerhans cells in cholesteatoma

Langerhans cells (LCs) are known to play an important role in the immunosurveillance system. In this study, as in others, numerous LCs were detected in the epithelial layer of acquired cholesteatoma by immunohistochemical staining. This finding suggests that cell-mediated immune responses are initiated by LCs in cholesteatoma; however, documentation concerning the microenvironment of LCs-keratinocytes in cholesteatoma is limited. Therefore, we investigated the effects of LCs on keratinocytes in vitro. To study these effects it was necessary to isolate and purify LCs. Our present study revealed that good enrichment and a high degree of purity (95%) of LCs could be obtained from neonatal rat skin using the immunomagnetic beads (Dynabeads M-450) sorting technique. These isolated LCs have the biologic activity of LCs, and Langerhans cells' conditioned medium (LCCM) stimulates DNA synthesis in thymocytes. The effect of LCCM on keratinocytes was then studied. We found that (1) LCCM stimulated DNA synthesis in keratinocytes was then studied. We found that (1) LCCM stimulated DNA synthesis in keratinocytes, but not protein synthesis, and (2) LCCM stimulated the incorporation of 3H-putrescine into keratinocytes by the activation of transglutaminase. Transglutaminase is a known marker of terminal differentiation in keratinocytes. By Western blot analysis, we identified a 17-kd immunoreactive mouse interleukin-1 alpha in LCCM. Our results imply that LCs found in cholesteatoma tissue may play an important role in stimulating both hyper-proliferation and cornification of keratinocytes; two characteristic features of cholesteatoma formation. These stimulatory effects may be due to the release of interleukin-1 or other factors by LCs.

The autologous mixed epidermal cell-T lymphocyte reaction is elevated in psoriasis: a crucial role for epidermal HLA-DR+/CD1a- antigen-presenting cells

The objective of this study was to determine whether epidermal cells (EC) from psoriasis lesions and uninvolved skin could stimulate autologous T lymphocytes in the in vitro autologous mixed epidermal cell-T lymphocyte reaction (autologous MECLR). The functional role of antigen-presenting cell (APC) subsets was concurrently determined in this reaction. Mononuclear cells and purified T lymphocytes from peripheral blood of psoriasis patients showed a clear proliferative response to autologous unpurified epidermal cells from involved as well as uninvolved skin. The autologous mixed leukocyte reaction (MLR) was not elevated in psoriasis patients. In healthy controls and contact allergy patients, T-lymphocyte proliferation was not observed either in the autologous MECLR or in the autologous MLR. The level of proliferation in the autologous MECLR from psoriasis patients correlated to the number of epidermal cells that were added. To exclude the possibility that the observed proliferation in the autologous MECLR in psoriasis was due to the presence of epidermal T lymphocytes that were being stimulated and expanded in vitro, the stimulator EC were gamma irradiated (30 Gy) in some experiments. Preincubation of EC with cyclosporin A (CsA) significantly inhibited the autologous MECLR. The CsA-induced inhibition could be neutralized by the addition of fresh untreated EC to these cultures. This indicated that one of the modes of action of CsA in resolving psoriasis is, as some investigators have already shown, via inhibition of epidermal accessory cell function. In the autologous MECLR, APC from psoriasis skin could initiate this reaction, whereas APC from peripheral blood could not. This occurred in an MHC class II restricted fashion. Depletion experiments showed that Langerhans cells (HLA-DR+/CD1a+) were not the principal stimulators of autologous T lymphocytes in the MECLR. These results indicated that mainly HLA-DR+/CD1a- epidermal cells from psoriasis patients could stimulate autologous peripheral blood T lymphocytes in an MHC class II-restricted fashion.

The kinetics of interaction between lymphocytes and magnetic polymer particles

Magnetic polymer-coated particles linked to antibodies are considered to be an efficient rosetting matrix for immunoselection. We have shown that a 20:1 bead:target cell ratio and a 90 min incubation period are the optimal conditions for specific binding of monoclonal antibody-labelled cells to goat anti-mouse IgG-coated beads. Higher ratios or longer incubation periods resulted in considerable non-specific binding. Characterisation of the optimal conditions for specific depletion of lymphocyte subpopulations showed that (a) a range of bead:target cell ratios and incubation periods can be used, with resulting high efficiency and specificity; (b) multiple monoclonal antibodies can be used simultaneously for the depletion of diverse lymphocyte subpopulations; (c) non-specific bead-to-cell binding does not affect the specificity and efficiency of magnetic depletion; (d) specific binding of one bead only was adequate for effective magnetic separation. These findings define the most economical, specific and efficient conditions of use of beads for negative immunoselection but preclude the use of beads as an analytical rosetting medium.

Isolation of epidermal Langerhans cells

Langerhans cells (LC) play an important role in the skin immune system. They are bone marrow-derived and function as the only accessory and antigen-presenting cells in the skin. Several techniques for enriching these cells have been devised, and four, including density gradient centrifugation, use of cell sorter, panning and immunomagnetic separation, are discussed. It is concluded that the most satisfactory method for isolation of LC is based on density gradient centrifugation and the most satisfactory for depletion of epidermal cell preparations for LC is based on the immunomagnetic principle.

T-cell response to purified protein derivative after removal of Langerhans' cells from epidermal cell suspensions containing keratinocytes expressing class II transplantation antigens

In a previous study we observed that human epidermal cell (EC) suspensions containing HLA-DR-expressing keratinocytes showed an amplified T-cell response to purified protein derivative (PPD). To evaluate further the possible immunological importance of class II transplantation antigens on keratinocytes we have compared the T-cell response to PPD in the presence of the following stimulator cells: EC suspensions from normal skin, or EC from tuberculin-reactive skin with or without removal of Langerhans' cells. The proliferation of purified T lymphocytes from peripheral blood in response to PPD in the presence of various concentrations of autologous EC was measured by [3H]thymidine incorporation on day 6. In 3 experiments out of 4 the EC from tuberculin-reactive skin, containing 28-76% HLA-DR-expressing cells as judged by immunocytochemistry (which also revealed fairly numerous HLA-DQ/-DP-expressing keratinocytes and a slight increase in CD36- and CD4- but not CD1-expressing cells), induced a more pronounced T-cell response to PPD than did normal EC. This was not the case in the fourth experiment, in which a small number of HLA-DR-(15%) and few if any HLA-DQ-/-DP-expressing keratinocytes were found. Immunomagnetic removal of CD1-reactive Langerhans' cells from the tuberculin-reactive EC suspensions resulted in a reduction of the T-cell response to PPD, in most cases down to background level (T cells alone + PPD). This study does not support the hypothesis that HLA-DR-expressing keratinocytes can in themselves act as antigen-presenting cells.