Shan Xu

Hydrogen peroxide mediates UV-induced impairment of antigen presentation in a murine epidermal-derived dendritic cell line

Abstract— Ultraviolet‐B (290–320 nm) radiation is known to impair the antigen‐presenting cell (APC) function of Langerhans cells (LC), skin‐specific members of the dendritic cell (DC) family. We sought to address mechanisms of this effect, focusing on the role played by hydrogen peroxide. For this purpose, we used a newly established murine DC line, XS52, which resembles epidermal LC in several respects. The APC capacity of XS52 cells, using two different CD4* T cell clones as responders, was inhibited significantly (>50%) by exposure to UV radiation (unfiltered FS20 sunlamps) at relatively small fluences (50–100 J/m2). Ultraviolet radiation also inhibited growth factor‐dependent proliferation of XS52 cells. On the other hand, cell surface phenotype was relatively well preserved after irradiation; expression levels of B7‐1 and B7‐2 were reduced slightly, while other molecules (e.g. Ia, CD54, CD1 la and CD18) were not affected. With respect to the role played by hydrogen peroxide, pretreatment with purified catalase (900 U/mL) prevented UV‐induced inhibition of APC function. Short‐term exposure to 3 miM H202 or f‐butyl H202 mimicked UV radiation by inhibiting APC function. Finally, intrinsic catalase activity was substantially lower in XS52 cells compared with Pam 212 keratinocytes. These results indicate that the generation of hydrogen peroxide alone is sufficient to produce some, but not all, of the deleterious effects of UV radiation on DC derived from the skin.

T Cell-Mediated Terminal Maturation of Dendritic cells

Numerous investigators have supported, with compelling evidence, the concept that the activation of naive T cells occurs primarily through antigens (Ag) presented by a distinct class of leukocytes known as dendritic cells (DC). As skin biologists, our own efforts have focused on Langerhans cells (LC), a unique population of DC that resides normally within the epidermis of skin and whose identification even predates knowledge about DC by more than one century. Three years ago, we initiated a program to develop long-term DC lines from the epidermis of mice, largely to accommodate the cellular homogeneity that is required for molecular biologic techniques, but also to facilitate the economic use of laboratory animals. Two concepts guided these efforts: 1) cells derived during the perinatal period would possess a highest proliferative potential, and 2) GM-CSF, which had promoted the survival and maturation of LC cultured by other investigators, would be essential. Our efforts were ultimately rewarded by the development of stable DC lines, termed the “XS series”, from specimens of epidermis in newborn BALB/c mice (1). These XS DC lines resemble resident LC in many respects, including: a) their dendritic morphology (1), b) Ag presenting capacity (1,2), and c) cytokine and cytokine receptor mRNA profiles (3–6). Importantly, our original XS cell cultures were “contaminated” by fibroblastoid cells, the “NS series,” which could be removed through their selective sensitivity to treatment with trypsin. Once this was accomplished, however, proliferation by the XS cells diminished substantially. We have determined subsequently that XS52 cells require for their optimal growth not only GM-CSF, which was added continuously to XS cell cultures, but also CSF-1, which was secreted in relatively large amounts by the NS cells (4). These XS lines and similar DC lines developed since that time have proven to be useful tools in our efforts to characterize the function of DC.

Establishment and characterization of antigen-presenting cell lines (XS series) derived from newborn mouse epidermis

Activation of naive T cells occurs primarily through antigen presentation by a distinct class of leukocytes, termed dendritic cells (DC) (reviewed in 1). Langerhans cells (LC) are a skin-specific member of this family and play a pivotal role in the induction of T cell-mediated immunity against various antigens that are present in or penetrate into skin, which include reactive chemicals (contact hypersensitivity), alloantigens (skin graft rejection), microorganisms (protective anti-infectious immunity), and tumor-associated antigens (protective antitumor immunity) (reviewed in 2). A major limitation in studying the biology of LC has been the absence of stable, long-term cell lines. To overcome this limitation, we have established a series of antigen presenting cell lines (XS series) from newborn BALB/c mouse epidermis (3,4). Here we describe the establishment and characterization of XS lines.