Ia+ murine epidermal Langerhans cells are deficient in surface expression of the class I major histocompatibility complex

Whole-Mount Preparation and Microscopic Analysis of Epidermis

The epidermis is a stratified epithelium. Compared to that for monolayered epithelia, understanding of the cell biology of stratified epithelia lags far behind. The major reason for this is the limitation of methods to reproduce the epidermis in vitro using cultured keratinocytes: for example, cultured keratinocyte cell sheets lack Langerhans cells, melanocytes, nerves, sweat ducts, and hair follicles. One current way to overcome this limitation is to observe the epidermis in vivo via whole-mount staining and three-dimensional imaging. Here, we describe how to prepare epidermal sheets from skin and how to immunostain and observe them in whole mount. © 2022 Wiley Periodicals LLC. Basic Protocol 1: Preparation of mouse epidermal sheets by the ammonium thiocyanate method Alternate Protocol: Preparation of mouse epidermal sheets by the dispase method Basic Protocol 2: Preparation of human epidermal sheets by the dispase method Basic Protocol 3: Whole-mount immunostaining of epidermis.

Biomarker evaluation of face transplant rejection: association of donor T cells with target cell injury

This series of 113 sequential biopsies of full facial transplants provides findings of potential translational significance as well as biological insights that could prompt reexamination of conventional paradigms of effector pathways in skin allograft rejection. Serial biopsies before, during, and after rejection episodes were evaluated for clinicopathological assessment that in selected cases included specific biomarkers for donor-versus-recipient T cells. Histologic evidence of rejection included lymphocyte-associated injury to epidermal rete ridges, follicular infundibula, and dermal microvessels. Surprisingly, during active rejection, immune cells spatially associated with target cell injury consisted abundantly or predominantly of lymphocytes of donor origin with an immunophenotype typical of the resident memory T-cell subset. Current dogma assumes that skin allograft rejection is mediated by recipient T cells that attack epidermal targets, and the association of donor T cells with sites of target cell injury raises questions regarding the potential complexity of immune cell interactions in the rejection process. A more histopathologically refined and immune-based biomarker approach to assessment of rejection of facial transplants is now indicated.

Damnacanthal, an effective inhibitor of LIM-kinase, inhibits cell migration and invasion

Damnacanthal is identified as an effective inhibitor of LIM-kinase. It inhibits chemotaxis of T-cells and migration and invasion of breast carcinoma cells in culture and hapten-induced migration of epidermal Langerhans cells in mouse ears. Damnacanthal is a useful tool for investigating the cellular and physiological functions of LIM-kinase.

LIM-kinases (LIMKs) play crucial roles in various cell activities, including migration, division, and morphogenesis, by phosphorylating and inactivating cofilin. Using a bimolecular fluorescence complementation assay to detect the actin–cofilin interaction, we screened LIMK1 inhibitors and identified two effective inhibitors, damnacanthal (Dam) and MO-26 (a pyrazolopyrimidine derivative). These compounds have already been shown to inhibit Lck, a Src family tyrosine kinase. However, in vitro kinase assays revealed that Dam inhibited LIMK1 more effectively than Lck. Dam suppressed LIMK1-induced cofilin phosphorylation and deceleration of actin retrograde flow in lamellipodia in N1E-115 cells. Dam impaired CXCL12-induced chemotactic migration of Jurkat T lymphocytes and Jurkat-derived, Lck-deficient JCaM1.6 cells and also inhibited serum-induced migration and invasion of MDA-MB-231 breast carcinoma cells. These results suggest that Dam has the potential to suppress cell migration and invasion primarily through the inhibition of LIMK kinase activity. Topical application of Dam also suppressed hapten-induced migration of epidermal Langerhans cells in mouse ears. Dam provides a useful tool for investigating cellular and physiological functions of LIMKs and holds promise for the development of agents against LIMK-related diseases. The bimolecular fluorescence complementation assay system used in this study will provide a useful method to screen for inhibitors of various protein kinases.

3D visualization of epidermal Langerhans cells

Langerhans cells (LCs) are intraepidermal dendritic cells that extend their dendrites between keratinocytes to form a dense network that covers the entire body. The mammalian epidermis has two diffusion barriers, the stratum corneum and tight junctions (TJs). In their resting state, LCs sit underneath these two barriers. Once activated, LCs elongate their dendrites to dock with, or penetrate through, TJs, which allows them to survey the environment between the two barriers. Here, we describe a method to visualize this dynamic interaction of TJs and LCs in 3D by using mouse ear epidermal sheets.

Keratinocytes function as accessory cells for presentation of endogenous antigen expressed in the epidermis

The precise contribution(s) of skin dendritic cells (DCs) to immune responses in the skin has not been well delineated. We developed an intradermal (i.d.) injection model in which CD8+ T (OT-I) cells that express ovalbumin (OVA) peptide-specific TCRs (Valpha2/Vbeta5) are delivered directly to the dermis of transgenic (Tg) mice expressing OVA in the epidermis. After i.d. injection, these mice reliably develop skin graft-versus-host disease (GVHD) by day 7. To determine the relative contribution of Langerhans cells (LCs) to the ensuing GVHD-like reaction, we generated K14-OVA x Langerin-diphtheria-toxin-receptor (Langerin-DTR) Tg mice to allow conditional ablation of LCs in the epidermis. To delineate the role of dermal DCs (dDCs) in the reaction, we also generated K14-OVA Tg chimeras using beta(2)-microglobulin-deficient (beta(2)m) congenic donor bone marrow cells. Dermal DCs in these mice cannot present OVA to autoreactive T cells (OT-I cells), whereas the LCs are antigen presentation-competent. Unexpectedly, OT-I cell injection into diphtheria toxin (DT)-treated beta(2)m --> K14-OVA x Langerin-DTR Tg mice resulted in skin GVHD. Thus, in vivo, both LC and dDC appear to be dispensable for the induction of keratinocyte-directed, CD8-mediated effector immune responses. Furthermore and surprisingly, OVA-expressing epidermal cells depleted of LCs that could not initiate allogeneic epidermal lymphocyte reactions activated naive OT-I cells in vitro. These results indicate that keratinocytes may function as accessory cells competent to prime naive skin-reactive T cells.JID JOURNAL CLUB ARTICLE: For questions, answers, and open discussion about this article, please go to http://network.nature.com/group/jidclub.

Host immune responses in ex vivo approaches to cutaneous gene therapy targeted to keratinocytes

Epidermal gene therapy may benefit a variety of inherited skin disorders and certain systemic diseases. Both in vivo and ex vivo approaches of gene transfer have been used to target human epidermal stem cells and achieve long-term transgene expression in immunodeficient mouse/human chimera models. Immunological responses however, especially in situations where a neoantigen is expressed, are likely to curtail expression and thereby limit the therapy. In vivo gene transfer to skin has been shown to induce transgene-specific immune responses. Ex vivo gene transfer approaches, where keratinocytes are transduced in culture and transplanted back to patient, however, may avoid signals provided to the immune system by in vivo administration of vectors. In the current study, we have developed a stable epidermal graft platform in immunocompetent mice to analyze host responses in ex vivo epidermal gene therapy. Using green fluorescent protein (GFP) as a neoantigen and an ex vivo retrovirus-mediated gene transfer to mouse primary epidermal cultures depleted of antigen-presenting cells (APCs), we show induction of GFP-specific immune responses leading to the clearance of transduced cells. Similar approach in immunocompetent mice tolerant to GFP resulted in permanent engraftment of transduced cells and continued GFP expression. Activation of transgene-specific immune responses in ex vivo gene transfer targeted to keratinocytes require cross-presentation of transgene product to APCs, a process that is most amenable to immune modulation. This model may be used to explore strategies to divert transgene-specific immune responses to less destructive or tolerogenic ones.

Phenotype and function of GM-CSF independent dendritic cells generated by long-term propagation of rat bone marrow cells

GM-CSF is believed to be an essential factor for growth and differentiation of myeloid dendritic cells (DC). Employing a low-density fraction of rat bone marrow cells, we attempted to generate DC with human Flt-3/Flk-2 and IL-6. In this culture system, typical DC gradually appeared without exogenous GM-CSF supplement. Phenotypes and functions of the DC were examined. Evidence provided that the most efficient long-term outgrowth of DC progenitors was obtained by GM-CSF independent culture systems with the aid of Flt3/Flk-2 and IL-6, not with c-kit ligand and IL-6. Furthermore, CD103 (OX-62), which is widely used for rat DC separation, was found to be insufficient for enriching DC, due to the down-regulation of the marker. However, the most efficient selection of rat DC was made by CD161a (NKR-P1A), a C-type lectin family. The GM-CSF independent DC was functionally active in vitro as well as in vivo assays.

Effects of T cell frequency and graft size on transplant outcome in mice

The features that determine whether graft-reactive T lymphocytes develop into effector cells capable of mediating organ destruction are not well understood. To investigate potential factors involved in this process, we first confirmed that female recipient mice acutely rejected minor Ag-disparate male skin, but not heart transplants. Despite this difference in outcome, heart and skin transplantation induced antidonor T cell responses of similar magnitude, specificity, and cytokine profile. The heart-graft-primed T cells transiently infiltrated the graft and ultimately induced the development of chronic transplant vasculopathy. Increasing the frequency of donor-reactive T cells by presensitization or by using TCR (CD8+ antimale)-transgenic recipients did not mediate acute rejection but accelerated the pace and severity of the vasculopathy. Surprisingly, decreasing the tissue mass of the donor heart by 50% resulted in acute rejection of these smaller grafts without increasing the frequency of antidonor effector T cells in the recipients. In complementary studies, placement of one or two male skin grafts on a single recipient did not affect the frequency or cytokine profile of the induced antimale T cell repertoire. Nonetheless, the recipients of single grafts acutely rejected the transplanted skin while the recipients of two skin grafts did not. These results provide new insight into the pathogenesis of transplant vasculopathy and provide an explanation for the difference in outcome between murine skin and heart transplants by highlighting the novel concept that the efficiency of transplant-reactive T cell immunity is heavily influenced by the tissue burden it encounters at the effector stage.

IL-1beta is essential for langerhans cell activation and antigen delivery to the lymph nodes during contact sensitization: evidence for a dermal source of IL-1beta

IL-1beta(-/-) mice manifest an impaired contact hypersensitivity response to the hapten trinitrochlorobenzene, with the principle defect expressed during the sensitization phase of this response. Following application of hapten to the skin, epidermal Langerhans cells of IL-1beta(-/-) mice failed to demonstrate the classical phenotype of activation. In addition, the delivery of epicutaneously applied fluorescein isothiocyanate to draining lymph nodes was decreased in IL-1beta(-/-) mice. Hapten delivery to draining lymph nodes could be restored by intradermal injection of recombinant IL-1beta. Reconstitution of lethally irradiated IL-1beta(-/-) mice by transfer of wild-type bone marrow restored hapten-stimulated IL-1beta mRNA expression, demonstrating that IL-1beta production was dependent on bone marrow-derived cells. In wild-type skin, IL-1beta expression was upregulated in a time- and dose-dependent fashion following hapten application. Interestingly, prominent IL-1beta expressing cells were found in the dermis, suggesting that dermal cells may contribute significantly to the contact hypersensitivity response.

A role for TGFbeta1 in langerhans cell biology. Further characterization of the epidermal Langerhans cell defect in TGFbeta1 null mice

Previous studies of TGFbeta1 null (-/-) mice indicated that the epidermis was devoid of Langerhans cells (LC) and that the LC deficiency was not secondary to the inflammation that is the dominant feature of the -/- phenotype (Borkowski, T.A., J.J. Letterio, A.G. Farr, and M.C. Udey. 1996. J. Exp. Med. 184:2417-2422). Herein, we demonstrate that dendritic cells could be expanded from the bone marrow of -/- mice and littermate controls. Bone marrow from -/- mice also gave rise to LC after transfer into lethally irradiated recipients. Thus, the LC defect in TGFbeta1 null mice does not result from an absolute deficiency in bone marrow precursors, and paracrine TGFbeta1 production is sufficient for LC development. Several approaches were used to assess the suitability of -/- skin for LC localization. A survey revealed that although a number of cytokine mRNAs were expressed de novo, mRNAs encoding proinflammatory cytokines known to mobilize LC from epidermis (IL-1 and TNFalpha) were not strikingly overrepresented in -/- skin. In addition, bone marrow-derived LC populated full-thickness TGFbeta1 null skin after engraftment onto BALB/c nu/nu recipients. Finally, the skin of transgenic mice expressing a truncated loricrin promoter-driven dominant-negative TGFbeta type II receptor contained normal numbers of LC. Because TGFbeta1 signaling in these mice is disrupted only in keratinocytes and the keratinocyte hyperproliferative component of the TGFbeta1 -/- phenotype is reproduced, these results strongly suggest that the LC defect in TGFbeta1 null mice is not due to an epidermal abnormality but reflects a requirement of murine LC (or their precursors) for TGFbeta1.

An immunocytochemical study of MHC class I expression on human Langerhans cells and melanocytes

Classical MHC class I glycoproteins (HLA-A, B, and C) present endogenous cytosolic peptide antigen fragments to CD8-positive T-cells. CD8-positive T-cell recognition and destruction of virus-infected cells are dependent on adequate cellular MHC class I expression. Constitutive MHC class I expression is ubiquitous, but known to be deficient on specific differentiated cell types which include hepatocytes, neurones, chondrocytes and myocytes. Although enabling assessment of MHC class I expression on individual cells, limitations of immunocytochemistry were encountered with this assessment on Langerhans cells and melanocytes. These dispersed intraepidermal cells were obscured by adjacent keratinocytes in sections immunostained for MHC class I glycoproteins. Initiatives designed to resolve the issue have included immunoelectron microscopy, cell culture techniques, and animal bone marrow chimera models. Despite the elegance of these techniques, the issue of MHC class I expression on Langerhans cells and melanocytes remains unresolved. In this immunocytochemical study, an alternative strategy was based upon the recognized deficiency of epithelial MHC class I expression within pilosebaceous adnexal units. Langerhans cells and melanocytes were therefore studied within this microenvironment of deficient MHC class I expression, using monomorphic and polymorphic MHC markers. Langerhans cells and melanocytes were demonstrated within pilosebaceous units of scalp skin by immunocytochemistry. Differentiation markers OKT6 (CD1a) and TMH1 defined Langerhans cells and melanocytes, respectively. Monomorphic MHC markers W6/32 and TAL IB5 defined invariant epitopes of HLA class I and II, respectively. Polymorphic MHC class I markers defined the HLA-Bw4 and HLA-Bw6 supertypic determinants. Constitutive MHC class I expression was shown to be deficient on Langerhans cells and melanocytes.

A role for endogenous transforming growth factor beta 1 in Langerhans cell biology: the skin of transforming growth factor beta 1 null mice is devoid of epidermal Langerhans cells

Transforming growth factor beta 1 (TGF-beta 1) regulates leukocytes and epithelial cells. To determine whether the pleiotropic effects of TGF-beta 1, a cytokine that is produced by both keratinocytes and Langerhans cells (LC), extend to epidermal leukocytes, we characterized LC (the epidermal contingent of the dendritic cell [DC] lineage) and dendritic epidermal T cells (DETC) in TGF-beta 1 null (TGF-beta 1 -/-) mice. I-A+ LC were not detected in epidermal cell suspensions or epidermal sheets prepared from TGF-beta 1 -/- mice, and epidermal cell suspensions were devoid of allostimulatory activity. In contrast, TCR-gamma delta + DETC were normal in number and appearance in TGF-beta 1 -/- mice and, importantly, DETC represented the only leukocytes in the epidermis. Immunolocalization studies revealed CD11c+ DC in lymph nodes from TGF-beta 1 -/- mice, although gp40+ DC were absent. Treatment of TGF-beta 1 -/- mice with rapamycin abrogated the characteristic inflammatory wasting syndrome and prolonged survival indefinitely, but did not result in population of the epidermis with LC. Thus, the LC abnormality in TGF-beta 1 -/- mice is not a consequence of inflammation in skin or other organs, and LC development is not simply delayed in these animals. We conclude that endogenous TGF-beta 1 is essential for normal murine LC development or epidermal localization.

Selective regulation of ICAM-1 and major histocompatibility complex class I and II molecule expression on epidermal Langerhans cells by some of the cytokines released by keratinocytes and T cells

Epidermal Langerhans cells (LC) are major histocompatibility complex (MHC) class II (Ia)-positive dendritic cells that act as potent antigen-presenting or accessory cells for primary and secondary T cell-dependent immune responses. Recent studies have disclosed that the morphological, functional, and phenotypic characteristics of LC are variably and drastically modulated by external stimuli both in vivo and in vitro. However, little is known of the biological significance of diverse cytokines in regulating the surface molecules of LC. To determine the regulatory properties of ICAM-1, Ia, and MHC class I (H-2K) molecules in LC, we have examined the effects of interleukin (IL)-1 alpha, IL-1 beta, IL-2, IL-3, IL-4, IL-5, IL-6, IL-7, IL-10, interferon-gamma (IFN-gamma), tumor necrosis factor-alpha (TNF-alpha), and granulocyte-macrophage colony-stimulating factor (GM-CSF) on the expression of these molecules. Among the cytokines examined, IFN-gamma markedly and reproducibly up-regulates the expression of H-2K, but not ICAM-1, in Ia+ LC in a time- and dose-dependent manner. TNF-alpha consistently up-regulates the expression of ICAM-1, but not H-2K, in a time- and dose-dependent manner. IL-10 slightly but reproducibly inhibits the expression of ICAM-1, but not H-2K, in a time- and dose-dependent manner. IL-10 potently inhibits the TNF-alpha-induced ICAM-1 up-regulation, but not the IFN-gamma-induced H-2K up-regulation. Moreover, no cytokine consistently affects the Ia expression of LC. In addition, slight enhancing effects have been observed on H-2K expression by IL-4, and on ICAM-1 expression by IL-1 alpha, IL-1 beta, or GM-CSF. The present data suggest that the selective regulation is operative in a certain cell surface moiety of LC by various cytokines. These results further facilitate our understanding of immunobiology of LC.

Skin graft rejection by beta 2-microglobulin-deficient mice

Mice homozygous for a beta 2-microglobulin (beta 2-m) gene disruption lack beta 2-m protein and are deficient for functional major histocompatibility complex class I (MHC-I) molecules. The mutant mice have normal numbers of CD4+8- T helper cells, but lack MHC-I-directed CD4-8+ cytotoxic T lymphocytes (CTLs). In this study we used the beta 2-m mutant mice to study the importance of MHC-I-directed immunity in skin graft rejection. Our results indicate that MHC-I-directed CD8+ CTLs are not essential in the rejection of allografts with whole MHC or multiple minor H differences. However, the absence of MHC-I-guided immunity profoundly reduces the ability of mutant mice to reject H-Y disparate grafts. In addition, we show that natural killer cells which vigorously reject MHC-I-deficient bone marrow grafts, are not effective in the destruction of MHC-I-deficient skin grafts.

Class I disparate corneal grafts enjoy afferent but not efferent blockade of the immune response

Class I antigens are normally expressed on cells in all three layers of the cornea. In congenic rats that differ only at the single Class I locus RT1 A, central orthotopic corneal grafts were rejected 18% of the time with a mean survival time (MST) of 11.5 days. Pre-immunized recipients always rejected Class I disparate corneal grafts (100%, MST = 13.3 days). Surprisingly, the presence of donor Langerhans cells in the cornea at the time of grafting did not increase the rejection of grafts (20%, MST = 14.0 days). To determine if long term surviving grafts enjoyed immune priviledged in the form of efferent blockade, the recipients were challenged with skin grafts 4 to 6 weeks following corneal transplantation. All of the corneal grafts underwent rejection (100%, MST = 14.7 days). A number of important conclusions may be drawn from these studies. A single Class I mismatch is a weak barrier to successful engraftment of corneal grafts. However if the recipient has previously been exposed to donor antigens, a single Class I disparity is sufficient to provoke rejection of all subsequent corneal grafts. The susceptibility of long term surviving grafts to rejection induced by skin grafts indicates the orthotopic corneal grafts are antigenic but not immunogenic.

Granulocyte macrophage--colony-stimulating factor (GM-CSF) decreases CD1a expression by human Langerhans cells and increases proliferation in the mixed epidermal cell-lymphocyte reaction (MELR)

Langerhans cells (LC) undergo a variety of phenotypic and functional changes in vitro. To determine the effects of granulocyte macrophage--colony-stimulating factor (GM-CSF), tumor necrosis factor-alpha (TNF-alpha), and interleukin 1-alpha (IL-1) on LC phenotype in vitro, epidermal cell suspensions were enriched for LC by density-gradient centrifugation and cultured in the presence of 10 ng/ml of these cytokines. The percentage of cells expressing the surface protein CD1a was determined by flow cytometry. This percentage typically dropped after 48 h culture in both control and cytokine-treated medium to less than half that of the starting value. By the fifth day, the percentage of cells expressing CD1a in TNF-alpha and IL-1--treated cultures was still near half of the starting value, slightly above that of control cultures. Treatment with GM-CSF caused large and consistent decreases in the percentage of epidermal cells expressing CD1a. Cell viability in each of the three cytokine-treated cultures was identical to the control cultures, with essentially all cells having died by the sixth day after isolation. To determine the functional effects of these cytokines, the cytokine-containing medium was replaced after 72 h with medium containing purified allogeneic T cells and proliferation measured. Preliminary experiments showed no increased proliferation induced by IL-1 or TNF-alpha--treated epidermal cells. GM-CSF-treated epidermal cells induced 2-3 times more T-cell proliferation than epidermal cells cultured without additional cytokines. We conclude that GM-CSF, a cytokine known to be produced by keratinocytes in vitro, decreases CD1a expression by human LC and increases their ability to stimulate proliferation by allogeneic T cells.

Recognition of keratinocytes by cytotoxic T cells specific for conventional HLA class-I alloantigen

This study analyzed whether human keratinocytes (KC) express conventional HLA class-I molecules as detected by class-I-specific cytotoxic T lymphocytes (CTL), and whether exposure of KC to interferon-gamma (IFN-g) is required for CTL recognition. Basal KC grown in serum-free medium and exposed to recombinant IFN-g for 24-96 h were used as targets in 51Cr-release assays. Target-cell susceptibilities to lysis were compared by analyzing the lytic unit (LU) activity of a given CTL population against IFN-g-treated and untreated KC. CTL effectors were cloned from alloantigen-primed cultures by limiting dilution in the presence of antigenic B lymphoblastoid cells (BCLL) and IL-2. These T-cell clones lysed appropriate BCLL and PHA blasts but not third-party BCLL or K562. Lysis of antigenic BCLL was specifically blocked by antibodies against CD3 or class-I antigens. Specificity of the clones for conventional class-I antigen was demonstrated by cytotoxicity tests employing a panel of HLA-typed BCLL. The clones specifically lysed KC syngeneic with the original effector immunogen, and lysis was also blocked by anti-class-I antibodies. The effect of IFN-g treatment was to increase KC susceptibility to lysis by these clones. From 3-25 times more LU were measured against IFN-g-treated KC than against nontreated KC, and the degree of enhancement was similar for KC treated with concentrations of IFN-g ranging from 2.5-200 U/ml. This effect of IFN-g treatment on KC lysis by CTL, which was detected after only 24 h at all doses tested, emphasizes the potential role of IFN-g in enhancing CTL-mediated antiviral epidermal immunity and in exacerbating epidermal disease mediated by specific lytic T cells. In addition, the finding that normal human KC can be recognized by MHC class-I-specific CTL demonstrates that KC do express conventional class-I-antigens and that KC lysis by CTL can occur independently of exogenous cytokines.

Characterization of a porcine CD1-specific mAb that distinguishes CD4/CD8 double-positive thymic from peripheral T lymphocytes

Porcine peripheral T-cells bear CD4 and CD8 cell surface antigens that distinguish helper from cytotoxic T-cells. In distinction from what has been found in other species, a large percentage of peripheral T-cells simultaneously express both CD4 and CD8. Monoclonal antibody 76-7-4 was found to stain all cortical and 7 +/- 3% of medullary thymocytes, Ia+ epidermal cells (i.e. Langerhans cells), no peripheral T-cells and 50% of peripheral B-cells. The antigen detected appears analogous to human CD1. All cortical thymocytes were also stained with CD4 and CD8 mAb. Since 76-7-4 did not stain peripheral T-cells, we conclude that CD4/CD8 dual-expressing peripheral T-cells are not simply immature thymic emigrants.

Murine epidermal Langerhans cells express significant amounts of class I major histocompatibility complex antigens

Epidermal Langerhans cells (LC) are leukocytes that express major histocompatibility complex (MHC) class II antigens and function as antigen-presenting and accessory cells. Caughman et al. [Caughman, S. W., Sharrow, S. O., Shimada, S., Stephany, D., Mizuochi, T., Rosenberg, A. S., Katz, S. I. & Singer, A. (1986) Proc. Natl. Acad. Sci. USA 83, 7438-7442] reported that LC are deficient in surface expression of MHC class I antigens, implying a specialization of these cells to class II-restricted antigen presentation. To readdress this obviously important issue, we have studied murine epidermal sheets prepared from B6 X BALB/c----B6 bone marrow chimeras 5 months after irradiation and bone marrow reconstitution. This enabled us to distinguish class I of LC from that of surrounding keratinocytes. When sheets were analyzed by immunofluorescence microscopy with monoclonal antibodies specific for donor class I antigens, donor-derived LC but not LC of recipient origin were stained. Appropriate controls for antibody isotype and MHC haplotype were negative. LC in epidermal cell suspensions, prepared from normal BALB/c and BALB/cBy mice (MHC haplotype d), were analyzed by flow cytometry as well as immunofluorescence microscopy. LC were stained by monoclonal antibodies to class I antigens of haplotype d, but not by isotype-matched control antibodies to class I antigens of haplotype k. We also found that LC were virtually depleted from epidermal cell suspensions by treatment with monoclonal antibodies to class I antigens of haplotype d and complement but not by treatment with control monoclonal antibodies and complement. Our data, therefore, show that LC express MHC class I molecules on their surface.

HLA class I antigen (heavy and light chain) expression by Langerhans cells and keratinocytes of the normal human epidermis: ultrastructural quantitation using immunogold labelling procedure

Using an immunogold labelling procedure, we quantified the density of major histocompatibility (MHC) class I antigens on the surface of Langerhans cells (LCs) and keratinocytes of the normal human epidermis. According to ultrastructural features, keratinocytes were divided into three subpopulations: stratum basalis (SBK), stratum spinosum (SSK), and stratum granulosum keratinocytes (SGK), and analyzed separately. For this purpose, three monoclonal antibodies (MCAs) were employed: an anti-HLA A,B,C, and anti-B2-microglobulin (B2-m), and a polymorphic anti-HLA A2 Aw69 MCA. Under electron microscopy, quantitative analysis demonstrated: (a) the presence of a high amount of HLA monomorphic determinants on SBK and SSK and moderate but significant labelling of SGK; (b) the very weak density of MHC class I antigens on the surface of epidermal LCs; (c) the expression, at an identical level, of the HLA heavy chain common determinant (HLA A,B,C), B2-m, and the alloantigen HLA A2 by all epidermal cells (ECs) apart from SGKs and LCs that presented far fewer HLA A2 sites than monomorphic determinants (B2-m and HLA A,B,C); (d) the absence of HLA class I on corneocytes and a moderate labelling of melanocytes. A knowledge of the precise quantitative distribution of HLA class I antigens among various cell subpopulations of the normal human epidermis would be very useful for the study and follow-up of cutaneous malignancies that are known to lose these molecules as well as for the understanding of immune responses, especially allospecific, that involve the skin.