Differential extracellular signaling via Fc gamma R and FMLP in functionally distinct antigen-presenting cell subsets: ultraviolet-induced epidermal macrophages versus Langerhans cells

The family of kallikrein-related peptidases and kinin peptides as modulators of epidermal homeostasis

The epidermis is the outermost skin layer and is part of one of the largest organs in the body; it is supported by the dermis, a network of fibrils, blood vessels, pilosebaceous units, sweat glands, nerves, and cells. The skin as a whole is a protective shield against numerous noxious agents, including microorganisms and chemical and physical factors. These functions rely on the activity of multiple growth factors, peptide hormones, proteases, and specific signaling pathways that are triggered by the activation of distinct types of receptors sited in the cell membranes of the various cell types present in the skin. The human kallikrein family comprises a large group of 15 serine proteases synthesized and secreted by different types of epithelial cells throughout the body, including the skin. At this site, they initiate a proteolytic cascade that generates the active forms of the proteases, some of which regulate skin desquamation, activation of cytokines, and antimicrobial peptides. Kinin peptides are formed by the action of plasma and tissue kallikreins on kininogens, two plasma proteins produced in the liver and other organs. Although kinins are well known for their proinflammatory abilities, in the skin they are also considered important modulators of keratinocyte differentiation. In this review, we summarize the contributions of the kallikreins and kallikrein-related peptidases family and those of kinins and their receptors in skin homeostasis, with special emphasis on their pathophysiological role.

Cutaneous dendritic cells

Cutaneous dendritic cells (DC) include epidermal Langerhans cells (LC), interstitial/dermal dendritic cells (DDC), as well as plasmacytoid DC (pDC) that occur under pathological conditions. These immune cells have a spectrum of different functions with implications that extend far beyond the skin. They have the potential to internalize particulate agents and macromolecules, and display migratory properties that endow them with the unique capacity to journey between skin and draining lymph nodes where they encounter antigen-specific T lymphocytes. Herein, we will review the features of human and mouse cutaneous DC, emphasizing characteristics representative of their life-cycle stages that occur within the skin.

Ultraviolet-B radiation induces modulation of antigen presentation of herpes simplex virus by human epidermal cells

Although ultraviolet (UV) B radiation is known to be immunosuppressive, there is little information regarding a relevant immunological endpoint to assess human subjects in vivo. Therefore, we have examined the effect of in vivo UV radiation on the ability of human epidermal cells (EC) to present herpes simplex virus (HSV) antigens to memory T cells. Human volunteers, who were seropositive for HSV, were exposed to one minimal erythemal dose (MED) for four consecutive days. EC, prepared from suction blister roofs, were co-cultured with autologous T cells in the presence of HSV. HSV antigen presentation by UV-exposed EC was increased compared with control, nonexposed EC. This up-regulation correlated with an influx of macrophages into the epidermis, which are considered to be associated with UV-induced tolerance. Altering the UV protocol to a sub-erythemal UV dose for four consecutive days or to a single high dose of 2 MED, resulted in suppressed HSV antigen presentation, without the influx of the UV-macrophages. One of the goals of the present study was to eventually use this HSV system to investigate sunscreen immunoprotection. A pilot study with a TiO2-containing sunscreen suggested that the endpoint for UV-induced immunosuppression presented here is promising to be used for human in vivo sunscreen immunoprotection studies.

The effects of ultraviolet radiation on the human immune system

The adverse outcome of increased ultraviolet (UV) irradiation on human health is currently of concern. While many experiments have been carried out in rodent models, fewer have been designed to test the effects of UV exposure in human subjects. This review concentrates on the modulations induced in the human immune system by UV, and outlines changes in antigen presentation by Langerhans cells and macrophages, in the activities of natural killer cells and T cells, and in cytokine regulation. Precautionary measures which might be taken to help protect people against the immunosuppressive action of UV irradiation are considered.

Temporal correlation between UV radiation locally-inducible tolerance and the sequential appearance of dermal, then epidermal, class II MHC+CD11b+ monocytic/macrophagic cells

We performed a time course study in order to define the in vivo relationship between the induction of active suppression of contact sensitization and the presence of various cells in ultraviolet-exposed dermis and epidermis implicated in locally inducible immune tolerance: class II major histocompatibility complex (MHC)+CD11b(lo)Gr-1- Langerhans cells (LC), class II MHC-CD45+CD3+ dendritic epidermal T cells, class II MHC+CD11b+Gr-1- monocytes or class II MHC+CD11b+Gr-1+ monocytic/macrophagic cells. Partial tolerance (50%) was first detectable 6 h after a single 72 mJ/cm2 ultraviolet B exposure and maximum tolerance at 48 h post-ultraviolet exposure. By flow cytometry, a low granularity LC subset had disappeared from the epidermis within 6 h after ultraviolet exposure, followed by a slower decrease in the high granularity Langerhans cells subset. Within the dermis at the 6-h time point, small numbers of infiltrating monocytic/macrophagic cells are already apparent. By 24 h post-ultraviolet exposure, at which time tolerance has increased to 70%, the infiltrating monocytic/macrophagic population had risen to 1.2% of the total dermal cell population and was observed for the first time in the epidermis along with other infiltrating leukocytes (i.e., polymorphonuclear leukocytes). By 48 h post-ultraviolet exposure, when a state of maximum tolerance is obtained, both constitutive epidermal and dermal antigen-presenting cell populations were at or near their nadir of depletion. The infiltrating monocyte/macrophage population, however, exhibited a dramatic increase in the epidermis at 48 and 72 h. Thus, the ability to locally induce a state of in vivo tolerance is closely associated with the expansion of class II MHC+CD11b+Gr-1+ and -monocytic/macrophagic cells in the dermis and epidermis.

Expression, but lack of calcium mobilization by high-affinity IgE Fc epsilon receptor I on human epidermal and dermal Langerhans cells

In atopic dermatitis (AD) patients, IgE molecules are demonstrated on the surface of Langerhans cells (LC). Fc epsilon RI molecules, which are present on the surface of LC in AD patients as well as normal individuals, are responsible for this binding. In this study, we have investigated phenotypic and functional characteristics of Fc epsilon RI on epidermal and dermal cell populations. Epidermal and dermal cell suspensions were prepared enzymatically with dispase followed by either trypsin or collagenase treatment, respectively. Peripheral blood basophils were negatively selected by excluding other leukocytes with surface marker staining. Consistent with previous reports, both peripheral blood basophils and epidermal LC were positively stained with anti Fc epsilon RI monoclonal antibody. In addition, an Fc epsilon RI positive population was demonstrated among dermal HLA-DR positive cells. These cells express significant amounts of HLA-DR molecules (DRHi) and co-express CD 1 a molecules, which identifies them as LC-like dendritic APC of the dermis. No other Fc epsilon RI positive population was found in the other dermal DRMid or DR- populations, except for a minor DRLo population, presumably mast cells. To analyze whether these Fc epsilon RI molecules are signal transducing for LC, intracellular calcium mobilization after crosslinking of Fc epsilon RI was measured with flow cytometry. Following crosslinking, peripheral blood basophils clearly increased intracellular calcium. On the other hand, neither normal epidermal LC nor dermal DRHiCD1a + cells changed their intracellular calcium level after Fc epsilon RI crosslinking. These data indicate that normal epidermal and dermal LC, but not basophils, are resistant to calcium flux following Fc epsilon RI engagement.

In human dermis, ultraviolet radiation induces expansion of a CD36+ CD11b+ CD1- macrophage subset by infiltration and proliferation; CD1+ Langerhans-like dendritic antigen-presenting cells are concomitantly depleted

Antigen-presenting (APC), suppressor T-cell-inducing macrophages infiltrate both human and murine epidermis after ultraviolet radiation (UVR) exposure. To determine their derivation, we prepared epidermal cell and dermal cell suspensions from human keratome biopsy specimens obtained from nonexposed skin and from UVB-irradiated sites (3 d after four times the minimal erythema dose). Simultaneous triple-marker flow cytometric analysis established the extended phenotype of macrophages infiltrating sunburned human epidermis (CD1a- CD1c- CD11b+ CD11c+ CD36+ Fc gamma RII+ DR+). This then enabled us to track dermal cells of this phenotype after UVR in relation to the heterogeneous DR+ populations in normal dermis. By both in situ immunohistology and cell suspension flow cytometry, UVR induced an expansion of bone marrow-derived DR+ cells in the perivasculature and sub-basement membrane zone of the papillary dermis. Despite an overall expansion of DR+ cells, the CD1a+ CD1c+ CD36- DR+ Langerhans-cell-like dendritic APC subset of dermal DR+ cells was depleted (p < 0.05), indicating that UVR-induced epidermal Langerhans cell loss (from 95% to 7% of DR+ epidermal cells) is not accounted for by Langerhans cell accumulation in the dermis. By contrast, UVR exposure induced a selective expansion of the dermal macrophage subset, which is phenotypically identical to the monocytic/macrophagic APCs that appear in the epidermis after UV injury (p < 0.01). Cell cycle analysis (to determine whether this expansion was accounted for entirely by infiltration) revealed no increase in the percentage of DR+ CD36+ UVR-exposed dermal cells in S/G2/M phase; however, the expanded DR+ CD36+ subset continued its already substantial level of proliferation unabated. Therefore, epidermal macrophages derive not only from transcapillary migration, but also from in situ proliferation of a dermal precursor. Taken together, these findings show that UVR creates an epidermal and dermal APC milieu which is dominated by monocytic/macrophagic cells, through depletion of cells of dentritic APC phenotype, and concomitant selective dermal expansion of a CD1a- CD1c- CD11b+ CD36+ Fc gamma RII+ DR+ (monocyte/macrophage) population.