Ultrastructural observation on Langerhans cells in the rat gingival epithelium

Ultrastructural determination of gingival Langerhans cells in alloxan-induced diabetic rats

The ultrastructure of Langerhans cells has not been fully investigated in diabetes-associated gingival tissues. The present study was carried out to investigate the ultrastructure of gingival Langerhans cells in alloxan-induced diabetic rats. Gingival biopsies were obtained from 22 diabetic and 18 control rats. Langerhans cells were observed by transmission electron microscopy (TEM) in the basal layers of healthy oral epithelium. On rare occasions, Langerhans cells were found in the suprabasal layers of the oral epithelium. Langerhans cells in the oral epithelium of diabetic rats were seen in the basal and suprabasal layers. Usually, Langerhans cells had clear cytoplasm and convoluted or indented nuclei and few or no specific granules. The clear cytoplasm contained mitochondria, lysosomes and a small number of rough-surfaced endoplasmic reticulum regions, but it lacked tonofilament. Occasionally, centrioles were also observed in the cytoplasm. The membrane of Langerhans cells had no junctional complexes such as desmosomes. In diabetic rats, Langerhans cell precursors were developed into specific granule-bearing cells. Both Langerhans cells and their granules were more frequent in the gingiva of diabetic rats than in the control group. These data suggest that Langerhans cells play an important role in explaining the pathogenesis and development of diabetic gingivitis.

Langerhans cell-like dendritic cells in the cornea, tongue and oesophagus of the chicken (Gallus gallus)

Langerhans cells are dendritic leucocytes which reside mainly within stratified squamous epithelia of skin and mucosa. Their visualization requires the use of ATPase histochemistry, electron microscopy for identifying the unique trilaminar cytoplasmic organelles (the Langerhans cell granules or Birbeck granules), and the expression of major histocompatibility complex class II molecules. Following uptake of antigen, Langerhans cells migrate via the afferent lymphatics to the lymph nodes and undergo differentiation from an antigen-processing cell to an antigen-presenting cell. Using the same approach as that employed in previous studies for the identification of chicken epidermal Langerhans cells, we show here the presence of ATPase-positive and major histocompatibility complex class II-positive Langerhans cell-like dendritic cells at the mucosal surface of the eye, tongue and oesophagus of the chicken. Ultrastructurally, these cells qualified as Langerhans cells except that they lack Langerhans cell granules. Thus, as in mammalian skin and mucosa, chicken mucosa contains mucosal dendritic cells with morphological and phenotypical features for the engagement of incoming antigens within epithelium and lamina propria.

Non-specific esterase-positive dendritic cells in epithelia of the frog Rana pipiens

Langerhans cells are antigen-presenting cells located in epithelia and have a dendritic outline, a convoluted nucleus surrounded by an electron lucent cytoplasm with sparse organelles and occasionally containing the characteristic Birbeck granule; their membrane contains class II molecules of the major histocompatibility complex and a strong membrane reactivity for both ATPase and non-specific esterase. Despite increasing knowledge about mammalian Langerhans cells, only a few studies have examined the possible occurrence of Langerhans-like cells in lower vertebrates. Our group has previously demonstrated the presence of dendritic cells in different epithelial membranes co-expressing a strong membrane ATPase reactivity and class II molecules of the major histocompatibility complex in the frog Rana pipiens. Adding another criterion in the characterization of Langerhans-like cells in amphibians, we now report evidence for the expression of membrane non-specific esterase reactivity in dendritic cells located in the epidermis, nictitant membrane and cornea with topographical and light and electron microscopical characteristics identical to those previously described for dendritic cells positive for ATPase and major histocompatibility complex class II in Rana pipiens. We postulate that, taking all this data together, these dendritic intraepithelial cells constitute the amphibian counterpart of mammalian Langerhans cells.

ATPase and MHC class II molecules co-expression in Rana pipiens dendritic cells

Mammalian Langerhans cells are antigen-presenting cells located in different epithelia. These cells have a characteristic ultrastructural pattern, present a plasmatic membrane ATPase activity and constitutively express class II molecules of the major histocompatibility complex. ATPase-positive dendritic cells that are morphologically similar to Langerhans cells have also been found in amphibian epidermis. In order to demonstrate that ATPase-positive dendritic cells of amphibian epidermis express class II molecules and are present in other stratified epithelia, histochemical and immunohistochemical as well as ultrastructural analysis were performed. ATPase-positive dendritic cells and class II-positive dendritic cells were observed in epidermis, nictitant membrane and cornea. In epidermis the number of ATPase-positive dendritic cells was 656+/-186/mm2 while class II-positive dendritic cells was 119+/-45/mm2. Some ATPase-positive dendritic cells showed co-expression of class II molecules. These results suggest the existence of dendritic cell subsets in amphibians as is clearly demonstrated in mammals.

Immunophenotypic characterization of feline Langerhans cells

To carry out the characterization of feline Langerhans cells (LC), first described in 1994, we used a panel of monoclonal antibodies (MAb) known to react with human, canine and feline leukocyte membrane antigens (Ag). The immunolabeling was performed, at light microscope level, on frozen sections of feline skin and labial mucosa using an avidin-biotin-peroxidase technique, and at electron microscope level on epidermal cell suspensions using an immunogold technique. Out of the 52 MAb tested, six labeled basal or suprabasal DC cells in the frozen sections, either in epidermis or lip epithelium: MHM23 (anti-human CD18), CVS20 and vpg3 (respectively anti-canine and feline-major histocompatibility complex class II molecules), vpg5 (anti-feline leukocytes), vpg39 (anti-feline CD4) and Fel5F4 (anti-feline CD1a). These six MAb were used on suspensions, and labeled cells which showed no desmosomes or melanosomes, but contained 'zipper-like' structures similar to Birbeck granules (BG) in their cytoplasm, revealing they were LC. Consequently, feline LC are CD18-positive (CD18+), major histocompatibility complex class II-positive (Class II+), CD1a-positive (CD1a+), vpg5-positive (vg5+) and CD4-positive (CD4+). This immunophenotypic and ultrastructural characterization demonstrates that feline LC share many characteristics with their human counterparts, a fact that will allow us to study the role of feline LC in certain feline diseases such as Feline Immunodeficiency Virus (FIV) infection, since it has been shown that human LC cells are HIV-permissive, and to establish an animal model for human AIDS.

Epidermal Langerhans cells in the terrestrial turtle, Kinosternum integrum

In mammalian epidermis, Langerhans cells (LC) are the only antigen-presenting dendritic cells that possess the ectoenzyme adenosine triphosphase (ATPase) and constitutively express class II molecules encoded by the major histocompatibility complex. Recently, we demonstrated the presence of LC in chicken epidermis. The aim of the present study is to demonstrate the presence of LC-like cells in turtle Kinosternum integrum, epidermis by light and ultrastructural ATPase histochemistry. ATPase-positive dendritic cells were observed in epidermal sheets whose maximum mean number was 192 cells/mm2. Electron microscopy for ATPase stained sections showed an electrondense precipitate in the plasma membrane of dendritic clear cells located among basal and suprabasal keratinocytes, ultrastructurally similar to LC. In serial sections, some dendritic cells showed LC (Birbeck) granules. The present study demonstrates for the first time ATPase-positive dendritic cells, morphologically similar to LC, in reptilian epidermis.

Langerhans cells: structure, function and role in oral pathological conditions

Langerhans cells (LCs) are dendritic bone marrow derived cells situated suprabasally in most stratified squamous epithelia, such as the epidermis and the epithelium of oral mucosa, including the gingiva. Langerhans cells are thought to act as antigen-presenting cells (APC) during induction of immune responses. The exact role of Langerhans cells in the oral mucosa is not fully understood although several investigations suggest that these cells are involved in reactions to antigen challenge under both normal and pathological situations. In this paper the structure, phenotypic markers and derivation of Langerhans cells are reviewed. In view of recent findings, the immunological characteristics and the implications of Langerhans cells in pathologic oral reactions are discussed.

Effects of low or high doses of short wavelength ultraviolet light (UVB) on Langerhans cells and skin allograft survival

Since Langerhans cells (LC) are normally the only cells within the epidermis to express the class II major histocompatibility complex (MHC) transplantation antigens, depletion of LC could be expected to prolong skin allograft survival by reducing the antigenic disparity between host and recipient. To assess this hypothesis, donor C57BL mouse shaved dorsal trunk or tail skin was exposed to high (200 mJ/cm2) or low (40 mJ/cm2) doses of short wavelength ultraviolet light (UVB) before grafting on to the thorax of BALB/c mouse recipients of the same sex. These strains have different major and minor transplantation antigens. The effects of UVB treatments on LC were determined by electronmicroscopy. Skin grafted 1-14 days following a single high dose of UVB irradiation was ultrastructurally depleted of LC and survived significantly longer than unirradiated skin before being rejected. After a 21-day interval between exposure and grafting when LC were again present in the epidermis there was no significant difference between treated and control graft survival. Exposure to low dose UVB irradiation only significantly increased graft survival for skin transplanted 1-3 days after irradiation; skin grafted 4 days following irradiation survived for a similar period to unirradiated control skin grafts. Electronmicroscopy showed that the low UVB dose did not deplete LC from the epidermis. We conclude that after low dose UVB treatment the class II MHC antigens on the LC plasma membrane were lost temporarily, thus prolonging graft survival, but when the plasma membrane antigens were re-expressed graft survival returned to normal.(ABSTRACT TRUNCATED AT 250 WORDS)