Human epidermal cell-induced generation of alloreactive cytotoxic T-lymphocyte responses against epidermal cells. Requirement for DR-positive Langerhans cells

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.

Phenotype, ultrastructure, and function of CD1+DR+ epidermal cells that express CD36 (OKM5) in cutaneous T-cell lymphoma

This study investigated the phenotype and function of different antigen-presenting cells (APC) present within the epidermis of patients with cutaneous T-cell lymphoma (CTCL). Involved epidermis of CTCL compared with uninvolved was found to contain increased numbers of CD1+DR+ APC. This population was heterogeneous and comprised both leucocytes of a novel CD1+DR+CD36 (OKM5)+ phenotype and CD1+DR+CD36- indeterminate/Langerhans cells. The CD1+DR+CD36+ leucocytes did not express TcR-1, CD5, CD15, or CD22, and only a minor population expressed CD11, demonstrating that they were neither T nor B cells, and did not belong to the major CD11+ (OKM1+) blood monocyte population. Electron microscopy of purified CD36+ lesional epidermal cells (EC) demonstrated that they lacked Birbeck granules found on CD1(+)-selected Langerhans cells, and most cells exhibited features of indeterminate cells or macrophages. The capacity of EC from involved epidermis to present alloantigens was found to be increased relative to uninvolved epidermis in all patients tested, and this capacity was critically dependent upon the presence of CD45+DR+ bone marrow-derived cells but not on the presence of CD45-DR+ keratinocytes. Positive selection using MoAb against CD1 and CD36 demonstrated that both cell populations exhibited the capacity to stimulate T cells. The results indicate that a novel antigen-presenting cell population with a unique phenotype is present within involved skin of patients with mycosis fungoides. These cells express CD36 in addition to CD1 and have an ultrastructural appearance consistent with a dendritic antigen-presenting cell derivation.

Role of keratinocytes in human recurrent herpetic lesions. Ability to present herpes simplex virus antigen and act as targets for T lymphocyte cytotoxicity in vitro

In human recurrent herpetic lesions epidermal keratinocytes are induced to express HLA class II (DR) antigens. Keratinocytes derived from human split skin and cultured in vitro were induced to express HLA-DR but not -DQ antigens with IFN gamma preparations. These stimulated keratinocytes presented herpes simplex antigen directly to autologous blood-derived T lymphocytes in four of four subjects (stimulation indices: 1.5-2.7), suggesting that keratinocytes may have an accessory herpes simplex virus (HSV) antigen-presenting role in addition to the Langerhans cells and macrophages in herpetic skin lesions. Blood mononuclear cells from eight herpes simplex seropositive subjects which were activated in vitro by HSV antigen for 6 d showed cytotoxicity specific for HSV in infected autologous keratinocytes. This was significantly increased by prestimulation with IFN gamma (51-56% to 83-85%). In four of eight patients some cytotoxicity also occurred against uninfected, IFN gamma-stimulated keratinocytes. Lymphocyte subset analysis showed that cytotoxicity against HSV-infected, IFN gamma-stimulated keratinocyte targets was mediated by both CD3+ T lymphocytes and Leu 11b+ natural killer cells. T lymphocyte cytotoxicity was mediated by both CD4+ and CD8+ T lymphocytes, suggesting a cytotoxic role for the activated CD4+ lymphocytes that initially predominate in herpetic lesions.

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.

Growth and differentiation of human keratinocytes on extracellular matrix

Extracellular matrices (ECM) have been reported to enhance epithelial cell attachment and proliferation as well as to induce differentiation in vitro. Since ECM components are physiological constituents of the dermoepidermal basement membrane, we studied the growth and differentiation of human keratinocytes on ECM in order to determine the benefits of culturing epidermal epithelial cells (keratinocytes) on reconstituted basement membranes. Disaggregated epidermal cells were grown in primary and subcultures in liquid medium; the attachment of the cells was greatly enhanced by ECM and noted within the first few hours after seeding; cells formed small islets that reached confluence within 2-12 days depending upon the plating density and the type of culture (primary or passages). Histological and ultrastructural cross-sections of the cultures clearly indicated that a multilayered epithelium can be obtained including a basal cell layer, several intermediate cell layers with cytoplasmic organelles, intermediate size filaments, desmosomes, and keratohyaline granules, and an upper layer of anucleated cells. Using immunofluorescence, both pemphigus and pemphigoid (basal membrane zone) antigens were expressed. The keratin pattern noted indicated that these epithelia differentiate and keratinize but do not express a complete program of keratinization, a finding usually noted when cells are grown submersed. These data show that ECM favor epidermal cell proliferation and differentiation and suggest that they may be used to obtain large amounts of epidermal equivalent suitable for grafting and/or in vitro studies.

Functional effects of epidermal cell culture supernatants (ECCS) on human B-cell activation

Epidermal cells (EC) were cultured without stimulation and the effect of these EC culture supernatants (ECCS) on human in vitro B-cell response was determined. Supernatants obtained between Days 5 and 7 were able to replace monocytes in the antibody response to the particulate antigen trinitrophenyl-polyacrylamide (TNP-PAA). These results were obtained when highly monocyte-depleted cultures (less than 0.5% peroxidase-positive cells) were used and were reproduced with supernatants from several different EC cultures. ECCS could not substitute for T cells in the T-dependent response to TNP-PAA. They contained an interleukin 1 (IL-1) activity but no interleukin 2 or B-cell growth factor (BCGF) activities. We tested the effect of ECCS on the proliferative response of highly monocyte-depleted B cells cultured at low cell density costimulated with anti-u antibody and BCGF. ECCS had no BCGF-like activity of its own but did potentiate the effect of BCGF. Thus EC cultures produce IL-1-like factor(s) which act directly on the early stages of B-cell activation.

Major histocompatibility complex class II antigen (HLA-DR, DQ and DP) expression in human fetal skin

Monoclonal antibodies were used to analyse skin samples from human fetuses (15-19 weeks gestational age) for the presence of class II major histocompatibility antigens (HLA-DR, DQ and DP). Cells expressing these antigens were clearly demonstrated within the epidermis from a proportion (4/7) of cases and were completely absent from the others. The negative samples were uniformly those with an epidermis of three cell layers or less. Such material may prove useful in studying the induction of class II antigen expression and the role of these antigens in allostimulation.

The ultrastructure of human gingival Langerhans cells in health and disease

There was a statistically significant shift towards increased proportions of type I Langerhans cells (containing many Langerhans-cell granules) and reduced proportions of both type II Langerhans cells (containing few granules) and indeterminate cells in diseased oral epithelium when compared to healthy oral epithelium. Langerhans cells and indeterminate cells were also seen in the sulcular epithelium of healthy and diseased specimens but never in junctional or pocket-lining epithelium.