Anti-TGF-beta treatment prevents skin and lung fibrosis in murine sclerodermatous graft-versus-host disease: a model for human scleroderma.

Scleroderma, a debilitating acquired connective tissue disease, is characterized by fibrosis, particularly of the skin and lungs. Monocyte-produced TGF-beta1, a potent stimulus for collagen synthesis, is thought to drive the fibrosis. Here, we thoroughly characterize a murine sclerodermatous graft-vs-host disease (Scl GVHD) model for scleroderma that reproduces important features of scleroderma including skin thickening, lung fibrosis, and up-regulation of cutaneous collagen mRNA, which is preceded by monocyte infiltration and the up-regulation of cutaneous TGF-beta1 mRNA. Most importantly, we can prevent fibrosis in both the skin and lungs of mice with Scl GVHD by inhibiting TGF-beta with neutralizing Abs. The murine Scl GVHD model provides the unique opportunity to study basic immunologic mechanisms that drive fibrosing diseases and GVHD itself and will be useful for testing new therapies for these diseases.

In human skin, UVB initiates early induction of IL-10 over IL-12 preferentially in the expanding dermal monocytic/macrophagic population.

In contrast to Langerhans cells, which make interleukin (IL)-12, differentiated macrophages that infiltrate the epidermis 72 h after ultraviolet B (UV) irradiation potently produce IL-10 mRNA and secrete IL-10 protein. We asked whether differentiated UV macrophages in the epidermis acquired their activated, IL-10hi status as a result of entering the epidermis or as a result of encountering UV-induced changes in the dermal microenvironment. In this study, sequential section immunostaining directly showed dynamic and reciprocal changes of infiltrating CD11b+ macrophages and CD1a+ Langerhans cell loss in human epidermis and dermis after in vivo UV exposure in relation to the microanatomic localization of newly appearing dermal cells that stain for IL-10 mRNA by in situ hybridization. Using quantitative reverse transcriptase polymerase chain reaction on purified dermal cell subsets, the first significant rise in IL-10 mRNA occurred 6 h after UV in the dermal CD11b+ (CD1-, 3-, 24-, 56-) monocytic/macrophagic population. Significant induction of IL-10 mRNA 24 h post-UV was limited to the CD11b+ CD1- subset (p = 0.006). The fold increase of IL-10 mRNA relative to 0 h by the CD11b+ dermal monocytic/macrophagic population peaked at 24-48 h and tapered thereafter. Intense IL-10 production by macrophages in the epidermis appeared to follow dermal changes, with maximum production at 72 h, indicating migration/activation of this population from the dermis, and the remainder of dermal cells, depleted of monocyte/macrophages and Langerhans cell-like antigen-presenting cells, showed no increase in IL-10 at any time point post-UV. IL-10 protein-producing CD11b+ macrophages in the dermis were also documented by flow cytometry. IL-12 mRNA was differentially regulated from IL-10 after UV, in that IL-12 was consistently downregulated in the CD11b+ monocytic/macrophagic population (p < 0.0002). Taken together, monocytic/macrophagic cells with high IL-10 and low IL-12 expression initially appear in the dermis as early as 6 h, and then appear in the epidermis, implicating the dermis as the primary site of activation/signaling for IL-10 upregulation in cutaneous antigen-presenting cells.

The human hair follicle: a reservoir of CD40+ B7-deficient Langerhans cells that repopulate epidermis after UVB exposure.

The ability of skin to maintain its protective structural and functional integrity depends on both resident and circulating cells. Until now, it was thought that dendritic antigen presenting cells of epidermis (Langerhans cells) were replaced by circulating bone marrow derived precursors. Here we show by immunostaining studies of timed biopsies taken from human skin after ultraviolet exposure, that hair follicle is a critical reservoir of Langerhans cells that repopulate epidermis depleted of Langerhans cells by a single four minimal erythema dose of ultraviolet B. Immunostaining with antibodies to thymidine dimers showed that ultraviolet B only penetrated the superficial hair follicle opening, whereas deeper follicle was relatively protected. Langerhans cells migrating from hair follicle into epidermis 72 h after ultraviolet exposure have a partial deficiency of molecules important to T cell costimulation. We used four color flow cytometry to show that Langerhans cells isolated from epidermis 72 h after ultraviolet B can upregulate CD40 but not B7-1 or B7-2 expression in culture, suggesting a different phenotype of hair follicle Langerhans cells. Therefore, the hair follicle is a specialized immune compartment of the skin that serves as an intermediate reservoir of Langerhans cells between bone marrow and epidermis, and that may play a critical role in immune surveillance.