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From the Departments of Oral and Maxillofacial Surgery
I*
and Pathology,
Tohoku
University, Sendai, Japan; and the Molecular/Cancer Biology Laboratory
and Department of Pathology,
Haartman
Institute, University of Helsinki, Helsinki, Finland
| Abstract |
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| Introduction |
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DCs are the most capable antigen-presenting cells (APCs) required to initiate the immune responses. Langerhans cells are paradigmatic DCs that are present in the skin and oral and bronchial mucosa. Precursor Langerhans cells migrate to the epidermis via the hematogenous route. After an antigen capture, Langerhans cells migrate to the regional lymph nodes and convert into mature DCs that are capable of priming naive T cells.13 During the process of maturation, Langerhans cells show increased expression of MHC class II molecules and costimulatory molecules B71 (CD80) and B72 (CD86).14,15 This maturing process is also associated with a high level of expression of CD83 and CD40.13,16 These phenotypical changes in Langerhans cells are commonly observed in the maturation process of dendritic cells in general.12,13 This maturation process is assumed to be a prerequisite for priming naive T cells in the secondary lymphoid organs.12,13 There are two counterreceptors of B7 expressed on T cells: CD28 and CTLA-4. The CD28 ligation induces a positive signal for T cell proliferation and cytokine production.17 The role of CTLA-4 has been less evident, and is suggested to be involved in a peripheral T cell tolerance by transmitting negative signals.18 Another population of DCs has been identified in the human dermis that is characterized by the expression of factor XIIIa.19-21 These DCs, termed dermal dendrocytes, are as potent as Langerhans cells in their antigen presentation capacity in vitro21 and are involved in the pathogenesis of psoriasis.22
In this study we immunohistochemically investigated the possible involvement of Langerhans cells or factor XIIIa+ dermal dendrocytes in antigen presentation during the local immune responses in inflamed skin tissue autotransplanted to the oral cavity. We used CD1a and Lag as representative markers of Langerhans cells. Lag reacts specifically with a 40-kd glycoprotein present in human Birbeck granule, helping to identify Langerhans cells at the light microscopic level.23 We reveal here 1) phenotypical characterization of dermal Langerhans cells, suggesting their immunological activation and 2) identification of lymphatic vessels that contained these activated Langerhans cells. We discuss the roles of Langerhans cells, which are more active in the context of inflammatory skin tissue than is generally conceived.
| Materials and Methods |
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Autotransplantation of a forearm skin flap was performed for the reconstruction of an extensive defect in the oral cavity caused by curative resection of advanced oral squamous cell carcinoma. The skin flap included the epidermis, dermis, subcutaneous adipose tissue, underlying muscle fascia, and vascular pedicle. Twenty-one biopsy specimens were obtained during the second surgery, performed approximately 2 years after the primary surgery to revise the contour of skin flaps. Of these 21 cases of skin flaps, 15 were analyzed that were severely inflamed by Candida albicans infection. The inflamed dermis was extensively infiltrated by macrophages and neutrophils, and the fungal pathogens were confirmed by culture study.6 As a control, normal forearm skin (five cases) was sampled from the remnant tissue trimmed off at the time of the initial surgery.
Fixation
For immunohistochemistry and immunoelectron microscopy, biopsy specimens were fixed in periodate-lysin-4% paraformaldehyde (PLP) for 612 hours at 4°C.24 After they were washed in phosphate-buffered saline (PBS) containing sucrose, the fixed specimens were rapidly frozen in dry ice/acetone after embedding in OCT compound (Miles, Elkhart, IN). For immunofluorescence staining, parts of the biopsy specimens were immediately frozen without prefixation.
Single Immunohistochemistry (Enzyme-Linked)
PLP-prefixed frozen sections were used with the
biotin-streptavidin-peroxidase method (Histofine staining kit;
Nichirei, Tokyo, Japan). The chromogen was 3',3-diaminobenzidine
tetrahydrochloride (DAB) (Dojin, Kumamoto, Japan). The primary
antibodies used are listed in Table 1
.
The specificity was confirmed by replacing the primary antibodies with
PBS. The sections were counterstained with methyl green or hematoxylin.
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Positive cells were quantified by light microscopy (40 objective), using an ocular grid (the area of the grid was 0.0625 mm2). Ten noncontiguous and nonoverlapping squares were randomly chosen for the cell counting in the epidermis or dermis. We judged a cell with a nucleus and clear immunoreactivity to be a positive cell. Positive cells obviously in the vessel lumens were excluded in this assessment.
Immunoelectron Microscopy for CD86, CD83, and Lag
The same staining method as in light microscopic immunohistochemistry was used.25 The specimens were fixed in 0.5% glutaraldehyde for 30 seconds before DAB reaction and in 1% osmium tetroxide for 20 minutes after DAB reaction. After dehydration in ethanol, the specimens were embedded in Epon. Ultrathin sections were observed with a Hitachi H-600 electron microscope.
Double Immunofluorescence Staining
Frozen sections mounted on glass slides were fixed for 10 minutes in chilled acetone before use. The following combinations of double immunofluorescence staining were performed in five representative cases: 1) combinations of CD1a and B71, CD1a and B72, CD1a and CD83, or CD1a and Lag; 2) combinations of CD4 and CD45RA, or CD4 and CD45RO; and 3) combinations of factor XIIIa and CD4, factor XIIIa and CD68, factor XIIIa and CD1a, factor XIIIa and CD83, or factor XIIIa and Lag. In combinations 1 and 2, primary unlabeled mouse monoclonal antibody (B71, B72, CD83, Lag, CD45RA, or CD45RO) was applied overnight at 4°C. The sections were then washed and incubated for 2 hours at 4°C with fluorescein isothiocyanate (FITC)-conjugated goat anti-mouse Fab fragments (Jackson ImmunoResearch, West Grove, PA). The second-step immunostaining was carried out with phycoerythrin (PE)-conjugated anti-CD1a or anti-CD4. In combination 3, rabbit primary antibody (factor XIIIa) was detected by FITC-conjugated goat anti-rabbit antibody (Biosource International, Camarillo, CA), and mouse antibody (CD4, CD68, CD1a, CD83, or Lag) was detected by tetramethyl rhodamine isothiocyanate (TRITC)-conjugated goat anti-mouse antibody (Biosource International).26 The sections were observed and photographed with an Olympus AX-80 microscope.
Double Immunohistochemistry (Enzyme-Linked)
The following combinations of double immunohistochemistry were performed with PLP-prefixed frozen sections of eight representative cases: 1) combinations of Lag and B72, or factor XIIIa and B72; 2) combinations of CD4 and CD1a, CD4 and B72, CD4 and CD83, or CD4 and Lag; 3) combinations of CD1a and vascular endothelial growth factor receptor-3 (VEGFR-3),27 CD83 and VEGFR-3, Lag and VEGFR-3, B71 and VEGFR-3, B72 and VEGFR-3, factor XIIIa and VEGFR-3, or CD68 and VEGFR-3; 4) a combination of VEGFR-3 and PAL-E.28 The first-step immunohistochemistry was performed by the same method as for the single enzyme-linked immunohistochemistry, using 4-chloro-1-naphthol (Sigma, St. Louis, MO) or 3-animo-9-ethylcarbazole (AEC) (Vector, Burlingame, CA). After washing in 0.2 mol/L glycine buffer (pH 2.2) for 10 minutes, the second-step immunohistochemistry was carried out with the indirect method, using anti-mouse rabbit antibody conjugated with alkaline phosphatase as the secondary antibody (Dako, Glostrup, Denmark). The chromogen was Fast Red substrate (Sigma) or Vector Blue (Vector). For a combination of mouse and rabbit (factor XIIIa) antibodies, the treatment of the glycine buffer was omitted.
Semiquantitative Assessment of the Ratios of Double-Positive Cells to Dermal CD1a+ Cells in the Inflamed Skin
We semiquantitatively graded the ratios of cells positive for Lag, CD83, CD80, or CD86 to the dermal CD1a+ cells in the inflamed skin by double immunofluorescence staining.
Assessment of Proliferation Activity of CD4+ and CD8+ T Cells in the Dermis of Inflamed Skin
Double immunohistochemistry for CD4 or CD8 and Ki-67 was performed as follows in 15 cases (modified from Ref. 29 ). First, sections were stained with anti-CD4 or CD8 with DAB as a chromogen, using an indirect immunoperoxidase method. Then sections were left in an autoclave for 5 minutes at 120°C to retrieve Ki-67 antigen. The sections were stained with anti-Ki-67, using a Histofine kit; reacted with nickel-cobalt DAB; and counterstained with hematoxylin. The labeling index was measured as the number of Ki67+/CD4+ or Ki67+/CD8+ cells among 100 CD4+ or CD8+ cells.
| Results |
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CD1a+ cells formed a network in the epidermis, whereas dermal CD1a+ cells were only sparsely distributed. Epidermal Lag+ cells made up approximately a quarter of epidermal CD1a+ cells. There were no Lag+ cells in the dermis. Virtually no cells were found to be positive for B71, B72, or CD83, indicating an absence of activated Langerhans cells in the normal skin. CD4+ and CD8+ T cells were sporadically present only in the dermis. Factor XIIIa+ dermal dendrocytes were present adjacent to the vessels in the dermis (not shown).
Inflamed Skin (Autotransplanted Skin Flap)
Compared with the normal counterparts, the number of
CD1a+ cells decreased by half in the epidermis,
whereas dermal CD1a+ cells increased markedly.
Dermal CD1a+ cells were frequently located in the
clusters of lymphocytes (Figure 1)
.
Lag+ cells occurred in the dermis, whereas there
was a marked reduction of them in the epidermis. Dermal
Lag+ cells always coexpressed CD1a, constituting
a part of CD1a+ cells (about one-sixth) (Figure 2)
. B72+ or
CD83+ cells abounded in the dermis, showing a
typical dendritic shape, but they were quite scarce in the epidermis
(Figure 3)
. Double staining revealed that
the vast majority of dermal CD1a+ cells
coexpressed B72 and CD83, in contrast to a lack of B72 or CD83 in
epidermal CD1a+ cells (Figure 4)
. B71+ cells
were only observed in the dermis sporadically, amounting to 1/18th of
B72+ cells. B71+ cells
were particularly evident within the lumen of thin-walled vessels
(identified as lymphatic vessels; vide infra) (Figure 5)
. Factor XIIIa+
cells were located outside the cluster of lymphocytes, virtually
lacking contact with lymphocytes (Figure 6)
. They are partly positive for B72 or
CD68, but negative for CD1a, CD83, or Lag (not shown).
B72+/CD83+ mononuclear
cells abundantly located within the cluster of lymphocytes in the
dermis were judged to be activated Langerhans cells because of
positivity for CD1a and Lag (partly) and negativity for factor XIIIa.
These activated, dermal Langerhans cells projected their cytoplasmic
processes to the neighboring lymphocytes (Figure 7)
. Most lymphocytes aggregated in the
dermis were
CD4+/CD45RO+/CD45RA-,
contrasting with a sparse distribution of CD8+ T
cells (Figures 8 and 9)
. Almost all T cells expressed CD28
(not shown). Some VEGFR-3+ lymphatic vessels in
the dermis,27
but not PAL-E+ blood
vessels,28
contained mononuclear cells with a phenotype of
CD1a+/B71+/B72+/CD83+
and Lag+ (partly) (Figure 10)
. These mononuclear cells were also
judged to be activated Langerhans cells. Lymphocytes were admixed
within the lumen of the same lymphatic vessels. Neither factor
XIIIa+ dermal dendrocytes nor
CD68+ cells were found in the lumen of
VEGFR-3+ lymphatic vessels (not shown).
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| Discussion |
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We used CD1a and Lag as representative markers of Langerhans cells. Lag+ cells constituted a part of CD1a+ cells in both the epidermis and dermis. This could be explained by the facts that precursor Langerhans cells lack Lag+ Birbeck granules and Langerhans cells lose Birbeck granules during the migration from the epidermis.30 This suggested that the presence of Lag+ Birbeck granules is sufficient but not a prerequisite for the identification of Langerhans cells.31 Factor XIIIa+ dermal dendrocytes, another subpopulation of DCs in human dermis, do not express CD1a or Lag in situ.19,20 Langerhans cells were originally defined as epidermal dendritic-shaped cells of neural origin by Paul Langerhans in 1868,32 and their functions as APCs were identified later.12,13 With all of this taken into account, we designate abundantly distributed dermal CD1a+ cells in our materials as dermal Langerhans cells.
Dermal Langerhans cells expressed B72 abundantly but B71 sporadically in the inflamed skin. This predominant expression of B72 over B71 has already been demonstrated on CD68+ cells in human intestines.33,34 In vitro study of Langerhans cells suggested a crucial role of B72 in the induction of T cell proliferation with little dependence on B71.35 B72, therefore, could be an important molecule for costimulation by Langerhans cells. We observed the expression of CD83 on dermal Langerhans cells and a lack of CD83 on factor XIIIa+ dermal dendrocytes in the inflamed skin. This observation further supports the conclusion that dermal Langerhans cells in the inflamed skin are of mature DC phenotype.36 We also confirmed direct cell-to-cell contact between CD83+/B72+ dermal Langerhans cells and lymphocytes, suggesting that these Langerhans cells could function as APCs. These findings are consistent with in vitro data suggesting that the majority of antigen-presenting capacity resides in the CD1a+ Langerhans cell-like dendritic antigen-presenting cell population.37 The lack of CD83 on factor XIIIa+ dermal dendrocytes and the limited contact with lymphocytes suggest that they are not principal APCs in our specimens.
Our present data showed that CD4+ and CD8+ T cells had a proliferation activity with the labeling indices of Ki-67 antigen of 4.2% and 0.8%, respectively. These figures may be lower than the Ki-67 labeling index of CD8+ T cells in Epstein-Barr virus-associated gastric cancer (13%).29 Ki-67 expression in circulating blood T cells has been reported to be 1.1% in CD4+ T cells and 1% in CD8+ T cells in healthy individuals, and 6.5 and 4.3% in HIV-1-infected individuals, respectively.38 We speculate that CD4+ T cells were significantly proliferating in the locale, demonstrating ongoing responses between APCs and T cells. Our morphological method, therefore, could be an in vivo counterpart of mixed lymphocyte reaction in vitro. CD4+ T cells in inflamed skin tissue mostly showed a memory phenotype, suggesting that activated, dermal Langerhans cells would restimulate primed CD4+ T cells. Activated dermal Langerhans cells could also be stimulated by T cells via the CD40/CD40 ligand pathway.16 The communication between activated dermal Langerhans cells and primed T cells is possibly reciprocal.
There appears to be a variation among the patterns of costimulation by
B7 depending on the types of T cells. For example, the cytokine
production of Th1-type (interleukin-2 (IL-2) and interferon-
(IFN-
)), but not that of Th2-type (IL-4), requires the costimulation
of primed helper T cells by B7.39,40
And this
costimulation by B7 is more effective for the production of IL-2 than
that of IFN-
.41
These in vitro data are
consistent with the present in situ observations on the
possible activation of memory T cells by APCs.
We have also observed that Langerhans cells were located in lymphatic vessels, which probably represents a process of migration to the regional lymph nodes.42 It is of particular interest that Langerhans cells in lymphatic vessels are fully matured and thus able to express B71 as well as B72 and CD83.
In the present study, inflammation was chiefly caused by Candida
albicans infection. The main defense against fungi is provided by
the T-cell-mediated acquired immunity and the innate immunity by
macrophages or neutrophils.43
In the experimental model of
candidiasis, protective immunity by phagocytes is well correlated with
the Th1 response.44
The production of IFN-
and IL-2 by
Th1 cells is dependent on the costimulatory signal by
B7.39-41
IFN-
enhances the activities of macrophages
and neutrophils in the killing process of Candida
albicans,45
and IL-2 protects neutrophils from
apoptotic death.46
These further support our notion that
B72+ activated dermal Langerhans cells could
play a defensive role against fungi through restimulating memory
CD4+ T cells in our study.
In conclusion, we have morphologically demonstrated the occurrence of activated dermal Langerhans cells in inflamed skin, which express common phenotypes to mature dendritic cells. These cells could play important roles in the immune mechanisms against pathogens. It remains to be clarified how dermal Langerhans cells or factor XIIIa+ dermal dendrocytes are involved in the local antigen presentation in other inflammatory dermatoses.
| Acknowledgements |
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| Footnotes |
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Accepted for publication October 2, 1999.
| References |
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eber die Nerven der menschlichen Haut. Virchows Arch Path Anat 1868, 44:325-337
. Increased phagocytosis, killing, and calcium signal mediated by a decreased number of mannose receptors. J Clin Invest 1993, 91:2596-2601
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