Immunobiological consequences of acute and chronic UV exposure

Neuronal nicotinic alpha7 receptors modulate inflammatory cytokine production in the skin following ultraviolet radiation

The anti-inflammatory effects of the neuronal nicotinic receptor alpha7 (nAChRalpha7) are proposed to require acetylcholine release from vagal efferents. The necessity for vagal innervation in this anti-inflammatory pathway was tested in the skin, which lacks parasympathetic innervation, using ultraviolet radiation (UVB) to induce a local pro-inflammatory response. Cytokine responses to UV in mice administered chronic oral nicotine, a nAChR agonist, were reduced. Conversely, nAChRalpha7 knock-out mice exposed to UVB elicit an enhanced pro-inflammatory cytokine response in the skin. Altered pro-inflammatory responses correlated with changes in SOCS3 protein. These results demonstrate that nAChRalpha7 can participate in modulating a local pro-inflammatory response in the absence of parasympathetic innervation.

Converting relapsing remitting to secondary progressive experimental allergic encephalomyelitis (EAE) by ultraviolet B irradiation

We induced experimental allergic encephalomyelitis (EAE) in SJL/J mice, an animal model for multiple sclerosis (MS), using myelin oligodendrocyte glycoprotein (MOG)(92-106) peptide, following ultraviolet (UV) irradiation. While all control mice developed relapsing-remitting (RR)-EAE, UV irradiation induced secondary progressive (SP)-EAE in some of the mice. Although mild demyelination was observed with T cell infiltration in RR-EAE, large demyelinating lesions developed in SP-EAE with massive macrophage and neutrophil infiltration and immunoglobulin deposition, but with little T cell infiltration. UV irradiation induced higher anti-MOG antibody responses. In SP-EAE, lymphoproliferative responses and interferon-gamma production were decreased without alteration of interleukin-4.

Immune regulation by polysaccharides: implications for skin cancer

UV radiation causes sunburn, premature aging of the skin and is the major environmental carcinogen for squamous cell and basal cell skin cancer in humans. Besides causing mutations in DNA, UV radiation contributes to carcinogenesis by suppressing immune responses to highly antigenic, newly arising neoplasms. Strategies aimed at preventing UV-induced immune suppression, the mechanism of action of the agents used, and the significance of immune protection for prevention of skin cancer are reviewed. This review focuses on the use of plant polysaccharides to prevent immune damage triggered by UV radiation, an approach that goes beyond absorption of UV radiation by sunscreens as a means of reducing tissue damage. The efficacy and mechanism of action of these agents in preserving T cell-mediated immunity to model antigens in human beings and in laboratory animals are discussed.

Preservation of the delayed-type hypersensitivity response to alloantigen by xyloglucans or oligogalacturonide does not correlate with the capacity to reject ultraviolet-induced skin tumors in mice

Chronic exposure to ultraviolet radiation suppresses T cell-mediated immune responses and induces the formation of suppressor T lymphocytes that prevent the rejection of highly antigenic ultraviolet-induced skin cancers in mice. Tamarind seed xyloglucans and pectinic oligogalacturonides prevent suppression of delayed-type hypersensitivity immune responses in mice to Candida albicans and alloantigen caused by a single exposure of ultraviolet radiation. We therefore investigated the ability of these poly/oligosaccharides to prevent suppression of T cell-mediated immune responses and suppressor cell induction during chronic ultraviolet irradiation and to preserve the capacity of ultraviolet-irradiated mice to reject a transplanted, highly antigenic, ultraviolet-induced tumor. C3H/HeN mice were treated 3x per week for 12 wk with 15 kJ per m2 ultraviolet B radiation followed by application of the polysaccharides/ oligosaccharides. The delayed-type hypersensitivity responses to C. albicans and alloantigen were measured after 1, 6, and 12 wk of treatment. Following the 12th wk of treatment the remaining mice were injected with the highly antigenic ultraviolet-induced, syngeneic tumor cell line UV5497-5. The polysaccharides/oligosaccharides protected delayed-type hypersensitivity responses to C. albicans but not contact hypersensitivity responses to dinitrofluorobenzene for up to 6 wk of ultraviolet radiation after which protection declined and suppressor cells were observed. In contrast, the delayed-type hypersensitivity response to alloantigen was preserved for the entire 12 wk of ultraviolet irradiation. Despite protection of immunity to alloantigen, the transplanted tumor cells grew equally well in all ultraviolet-irradiated animals. These results indicate that delayed-type hypersensitivity responses are heterogeneous and that delayed-type hypersensitivity to alloantigen is not a surrogate marker for rejection of ultraviolet-induced skin tumors.

Effects of ultraviolet B light on cutaneous immune responses of humans with deeply pigmented skin

The incidence of skin cancers of the basal and squamous cell types is extremely low among genetically black-skinned human beings, whereas these types of skin cancers are common among Caucasians, especially those who live in geographic areas of high sun exposure. Ultraviolet B light (UVB) is thought to be the primary oncogenic agent in sunlight. We have recently demonstrated that acute, low-dose exposure of Caucasian skin to UVB impairs the induction of contact hypersensitivity to dinitrochlorobenzene (DNCB) in approximately 40% of normal individuals. Importantly, this trait--termed UVB susceptibility--was found to be a characteristic of virtually 100% of patients with a history of biopsy-proved skin cancer, implying that UVB susceptibility may be a risk factor for this disease. Because melanin pigment is thought to be protective of some of the deleterious effects of UVB radiation, we have examined the capacity of a low-dose regimen of UVB to alter induction of contact hypersensitivity in individuals with genetically melanized or heavily tanned skin. Our results indicate that UVB radiation depletes heavily pigmented skin of Langerhans cells, just as it does in Caucasian skin. Moreover, UVB-susceptibility exists as a polymorphic trait in individuals with genetically determined black skin, as well as in individuals with heavily tanned skin, and the incidence of this trait is similar to that found among normal Caucasian subjects. Thus, melanin does not appear to protect against the deleterious effects of an acute, low-dose regimen of UVB on induction of cutaneous immunity, and the UVB susceptibility trait is equally well-represented in both black- and Caucasian-skinned individuals. We conclude that although UVB susceptibility may function as a risk factor for skin cancer in Caucasians, it does not function similarly in black-skinned human beings, probably because melanin effectively protects against the mutagenic properties of UVB radiation.

Skin suction blister wound exposed to u.v. irradiation: a burn wound model for use in humans

The effects of exposing blister wounds to u.v. irradiation were assessed in 14 male volunteers, on whose forearms blister wounds (diameter 5 mm, suction set at 200 mmHg below atmospheric for 2 h 15 min, blister roof cut at base), and irradiated blister wounds (as above, in addition u.v. irradiation given selectively for 30 min from a distance of 10 cm), were produced. In non-u.v.-irradiated wounds, flow cessation, assessed by video microscopy (n = 6), was observed in a small proportion of the papillary loop vessels. The oedema adjacent to the wound was poorly developed. Laser Doppler linear scans (n = 8) demonstrated a pronounced hyperaemia in the wound bed and also in the adjacent skin, the reaction subsiding over a few days. The exudation rate, determined by weighing the hydrocolloid dressings applied to the wound, was maximal on day 1 and then rapidly decreased. Epithelialization, assessed evaporimetrically as the time taken for reinstatement of the epidermal water barrier, was complete in 5.1 days. In the u.v.-irradiated wounds the blood flow had ceased in all the papillary loop vessels by day 1, and increased oedema, exudation and hyperaemia at the wound edges were observed. Epithelialization was not significantly retarded by the irradiation injury. After 6 months, slight discolouration of the skin was occasionally observed, but no cosmetically disturbing scars. This benign and standardized wound model in humans--based on a combination of a mechanical suction injury and a superficial radiation burn--may prove to be useful, for instance when studying the effects of burns treatment.

Susceptibility to effects of UVB radiation on induction of contact hypersensitivity as a risk factor for skin cancer in humans

Normal, healthy human volunteers and patients with proved history of non-melanoma skin cancer have been tested for their capacity to develop contact hypersensitivity to dinitrochlorobenzene (DNCB) following exposure of buttock skin to acute, low-dose ultraviolet B (UVB) radiation. Using a radiation protocol that achieves virtually complete depletion of normal-appearing Langerhans cells from irradiated skin, it was learned that approximately 60% of healthy volunteers developed vigorous contact hypersensitivity (CH) when 2000 micrograms DNCB was painted on the irradiated site. These individuals were designated UVB-resistant, and were distinguished from other individuals, designated UVB-susceptible, who failed to develop contact hypersensitivity following an identical treatment protocol. It was then discovered that virtually all (92%) skin cancer patients exposed to UVB and DNCB failed to develop CH, i.e., were UVB-susceptible. In subsequent experiments, epicutaneous application of 2000 micrograms DNCB to unirradiated skin of UVB-susceptible individuals revealed a further distinction between normal persons and skin cancer patients. Approximately 45% of the latter (and none of the former) remained unresponsive (failed to develop contact hypersensitivity following this second attempt at sensitization), implying that they had been rendered immunologically tolerant. These tolerant individuals responded normally to the unrelated hapten, diphencyprone. We conclude that human beings resemble inbred strains of laboratory mice in that some individuals are UVB-susceptible, whereas others are UVB-resistant. Because the incidence of UVB-susceptibility was significantly higher in skin cancer patients, and as specific unresponsiveness could be demonstrated only in these patients, we propose that UVB-susceptibility, as we define it in this hapten system, may be a risk factor for the development of skin cancer.

Photoimmunology: the mechanisms involved in immune modulation by UV radiation

Ultraviolet radiation (UVR) may be the most prevalent agent that man encounters in his environment. As a result, certain biological adaptations take advantage of the beneficial effects of UVR exposure, e.g. the photoactivation steps involved in vitamin D metabolism. In this regard, UVR plays an important role in maintaining our good health; however, it must be noted that UVR is potentially the most harmful naturally occurring agent in our environment. Thus, it appears that several mechanisms have evolved to protect us against the detrimental effects of UVR overexposure. Although epidermal melaninization or "tanning" may be the most obvious example of these processes, we would argue that adoptive mechanisms within the immune system also provide protection against UVR-induced skin damage. It is now known that UVR affects the distribution and functional activities of various immunocompetent cells within the skin, as well as modifying the production of inflammatory and hematopoietically active cytokines. This review will focus on the known mechanisms involved in the immune modulatory effects of UVR and how adoptive immune responses to UVR-induced skin damage contribute to specific pathological processes.

Cross-reactive tumor antigens in the skin of mice exposed to subcarcinogenic doses of ultraviolet radiation

This study suggests that cross-reactive tumor-associated antigens (TAA) are induced in the epidermis of mice exposed to subcarcinogenic doses of ultraviolet radiation (UVR). Foot-pad immunization of C3H mice with viable epidermal cells from syngeneic UVR-exposed mice induced cytotoxic cells in the draining lymph nodes (DLN). These cells were capable of lysing a battery of UVR-induced tumor targets in a short-term chromium release assay. In contrast, the DLN cells of mice immunized with epidermal cells from normal non-UVR-exposed mice did not mature into effector cells with antitumor activity. The spectrum of tumor recognition of cytotoxic cells induced by immunization with UVR-exposed epidermal cells was identical to that of cytotoxic T cells obtained from animals that were foot-pad immunized with UVR-induced tumor cells. Both cytotoxic cell populations were shown to lyse tumors of diverse origin, including syngeneic UVR- and methylcholanthrene-induced tumors, as well as allogeneic UVR-induced tumors. These cells displayed minimal lytic activity against YAC-1 lymphoma cells, peritoneal exudate cells, and concanavalin A-stimulated splenocytes. The results from this study demonstrate that antigens are expressed on UVR-exposed mouse epidermal cells prior to the emergence of skin tumors, and these antigens can induce cytotoxic cells with specificity for TAA. We conclude that the early antigenic changes observed in UVR-exposed epidermis and their effect on the host's immune system may influence the emergence and progression of UVR-induced skin cancers.