Effect of psoralens and ultraviolet radiation on murine dendritic epidermal cells

Monofunctional psoralens produce less phototoxicity than bifunctional psoralens after ultraviolet A (UVA) irradiation. We investigated the effect of repetitive treatments with angelicin (isopsoralen), a monofunctional psoralen, plus UVA radiation (IPUVA) on the number and morphology of dendritic epidermal cells (dEC). This effect was compared with that of 8-methoxypsoralen plus UVA radiation (PUVA), UVA alone, and UVB radiation. C3H/HeN mice were treated topically with the drugs three times/wk for 4 consecutive wk; followed each time by 1 or 2.5 J/cm2 of UVA radiation. Other groups of mice were treated with the drugs alone, UVA alone, or 0.81 J/cm2 of UVB. Epidermal sheets were stained for ATPase, Ia, and Thy-1 markers. Mice treated with PUVA and UVB exhibited severe phototoxicity, whereas no overt phototoxicity was observed in mice treated with IPUVA, UVA alone, or the drugs alone. Early during the PUVA and UVA treatments the ATPase marker was lost from dEC, followed by loss of the Ia marker; the Ia marker was lost before the ATPase marker from dEC in animals treated with IPUVA. At the end of the treatment, however, nearly total depletion of ATPase+, Ia+, and Thy-1+ dEC was observed in mice treated with PUVA and IPUVA. UVB radiation caused rapid depletion of Thy-1+ dEC as well as ATPase+ and Ia+ cells. During treatments with IPUVA, PUVA, UVA, and UVB, the Langerhans cells became rounded and lost their dendrites. These changes were quantitated by image analysis. We conclude that alterations of cutaneous immune cells can occur in the absence of overt phototoxicity, and that monofunctional and bifunctional psoralens plus low dose of UVA radiation may have different effects on dEC markers.     

即时型PUVA对郎格罕细胞和接触过敏的影响

在实验动物中研究了即时型光化学疗法对表皮郎格单细胞数量和形态的影响及对接触过敏反应的抑制，并与常规使用的光化学疗法进行了对比，结果表明二种方法间无差异，３Ｊ/ｃｍ２的即时型光化学疗法无红斑反应并能引起郎格罕细胞数量和形态的变化，并且通过诱导抑制性淋巴细胞抑制接触过敏反应。还探讨了有关致癌的可能性。     

In vivo PUVA and UVB sensitivity of various human epidermal Langerhans cell markers (ATPase, HLA-DR and T6)—Dose-response and time-sequence studies

To form a comprehensive view of the UV-sensitivity of human epidermal Langerhans cells (LC), the time-sequence and close response effects of single doses of UVB or 8-methoxypsoralen plus UVA (PUVA) radiation on three different LC surface markers were studied with histochemical and immunohistochemical staining. An increasing PUVA dose from 1 to 10 J/cm² caused an almost linear decrease in the surface enzyme (ATPase) positive LC count, whereas the cell surface antigens (HLA-DR and T6) were rather more resistant, up to a PUVA dose of 5 J/cm². A single dose of 5 J/cm² of PUVA induced an LC depletion that was similar during the 21 days of observation, irrespective of whether the cells were visualized with ATPase staining or with monoclonal antibodies against the cell surface antigens HLA-DR or T6. In each case, the nadir was reached 14 days after irradiation; the average residual LC count was then 57%. The cell counts 21 days after PUVA irradiation were still only approximately 74% of the nontreated skin counts. Langerhans cell depletion induced by an erythemagenic dose of UVB irradiation was swifter and more pronounced than that induced by 5 J/cm² of PUVA but, again, a similar time schedule was recorded with ATPase, HLA-DR and T6 staining.     

Surface densities of murine Ia+ dendritic epidermal cells (Ia+DECs) and Thy-1+ dendritic epidermal cells (Thy-1+DECs) in relationship to aging and ultraviolet B (UVB) radiation

Identification and enumeration of both Ia + dendritic epidermal cells (Ia + DECs) and Thy-1 + dendritic epidermal cells (Thy-1 + DECs) from various parts of the body and non-irradiated and ultraviolet B (UVB) irradiated back skin were examined using epidermal sheets of C3H/He inbred mice of different age groups and indirect immunofluorescent technique. The following results were obtained: [1] There was a significant decline in both Ia + DEC and Thy-1 + DEC density in the mice in the oldest group (48–50 weeks); [2] The densities of Ia + DECs were significantly higher than those of Thy-1 + DECs in comparisons of various parts of the body; [3] At 24 h after 60–120 mJ/cm² UVB irradiation, the Ia + DECs and Thy-1 + DECs decreased significantly in a dose-dependent fashion. The Ia + DECs decreased drastically (p<0.01) while the Thy-1 + DECs decreased mildly (p<0.05). [4] The degree or resistance to UVB differed between Ia + DECs and Thy-1 + DECs in older mice (40–48 weeks). These findings may imply that the decline of the Ia + DECs and Thy-1 + DECs reflects alterations in immune response during aging; As do Ia + DECs, Thy-1 + DECs might also play a role in UVB induced specific unresponsiveness in contact hypersensitivity; each type of Ia + DECs and Thy-1 + DECs follows a distinct biological kinetic pattern after UVB irradiation.     

Morphological changes in the proximal area of the rat's hair follicle during early catagen

Summary In human adult volunteers, oral 8-methoxypsoralen and UVA (PUVA) caused an almost linear dose-response effect in depleting adenosine triphosphatase positive epidermal Langerhans cells (LC) when irradiations of 1–5 J/cm² were used. A higher dose did not appreciably augment the LC depleting effect although the intensity of the PUVA-induced skin inflammation increased. After a single PUVA dose of 5 J/cm², a nadir in LC density was achieved on day 8 after irradiation, with a decrease from the starting mean count of 704 ± 58 cells/mm² to 195 ± 173 cells/mm². On day 15 after irradiation, the LC count was still low (261±249 cells/mm²). In comparison, a single erythematogenic irradiation with a medium-pressure mercury lamp emitting mainly UVB caused an LC depletion which was less intensive, peaked earlier and was almost completely restored by day 15. With both modalities morphological changes were induced in the LC, manifested initially as a shortening of the dendritic processes and later as cell enlargement and dendrite elongation.     

Sunscreens protect epidermal Langerhans cells and Thy-1+ cells but not local contact sensitization from the effects of ultraviolet light.

This study compares the ability of two commonly used sunscreens--octyl dimethyl para-aminobenzoate (Padimate O) and 2-ethylhexyl-p-methoxycinnamate (2-EHMC)--to protect Langerhans cells (LC), Thy-1+ dendritic epidermal cells (Thy-1+ dEC), and local contact sensitivity (CS) from the effects of ultraviolet (UV) light. Chronic exposure of mice 5 d per week for 4 weeks with an intermediate dose of solar-simulated sunlight from which any UVC had been filtered reduced the LC and Thy-1+ dEC density of murine epidermis. This irradiation procedure was designed to simulate closely the daily exposure of humans to sunlight. This effect on LC and Thy-1+ dEC occurred in both albino and pigmented mice that develop a tan during the irradiation procedure, indicating that a tan does not protect these cells from the effects of UV light. Sunscreen preparations with Padimate O and 2-EHMC, both of which also contained benzophenone-3, as well as Padimate O or 2-EHMC in organic solvent, inhibited UV light from depleting LC from the epidermis of both mouse strains. Padimate O and 2-EHMC in organic solvent were used to ensure that these were the active ingredients in the sunscreen preparations. In contrast to the effects on LC, Padimate O, but not 2-EHMC, protected Thy-1+ dEC from UV exposure in both mouse strains, but neither protected against the development of local immunosuppression using a contact sensitivity model. Thus, even in a mouse strain that is sensitive to UV-induced immunosuppression, local immunosuppression can occur in the presence of normal densities of LC and Thy-1+ dEC.     

Rapid induction of Thy-1 antigenic markers on keratinocytes and epidermal immune cells in the skin of mice following topical treatment with common preservatives used in topical medications and in foods

Earlier experiments from our laboratory revealed that the medication most commonly used for depigmenting patients with vitiligo, monobenzyl ether of hydroquinone (MBEH), when applied to the skin of DBA/2 mice caused an increase in the population density (cells/mm2) of identifiable Ia+ and ATPase+ Langerhans cells. Further, this increase in Langerhans cell density could be correlated with an increase of contact hypersensitivity (CHS) reactivity to dinitrofluorobenzene (DNFB). The current experiments demonstrated that other compounds chemically similar to MBEH, such as butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA), which are used as preservatives/antioxidants in many topical medications, cosmetics, food, and rubber products, can in five days significantly increase the population density of Thy-1+ dendritic epidermal cells. These compounds had no effects on Ia+ cells. This observation suggests that the Thy-1+ DEC cells may be more mobile and/or their surface markers may be readily expressed and are not a slowly mobile (trafficking) population of cells as suggested by the results of previous work. In addition, these parasubstituted phenolic compounds behaved like pertussis toxin and induced Thy-1 and Ia expression on keratinocytes. These changes in Thy-1 immune markers were not accompanied by functional alterations in the immune response to contact allergens as measured by the ear swelling technique.     

Alterations in cutaneous immune reactivity to dinitrofluorobenzene in graying C57BL/vi.vi mice

The fur of the C57BL/vi.vi mouse is black at 6 weeks of age. By 6 months of age the animals are white and there are no identifiable pigment cells within the epidermis or hair bulbs. Human subjects with vitiligo exhibit loss of epidermal pigment cells. The loss of pigment cells in human subjects with vitiligo has been associated with loss of cutaneous immune reactivity to contact allergens. Therefore, studies were performed to determine whether loss of pigment cells in these depigmenting mice also was associated with loss of the cutaneous immune response. The number of Ia-positive (Ia +) Langerhans cells (LC)/mm2 on the back and the ear, the sites of sensitization and challenge with dinitrofluorobenzene (DNFB), was quantified before, during, and after depigmentation. We observed that there were fewer LC/mm2 on the back and the ear before and after pigment loss in the graying mice than in the normal control C57BL/6 mice. The young pigmented C57BL/vi.vi mice were capable of developing moderate contact hypersensitivity; the older depigmented mice did not sensitize to DNFB. We conclude that the depigmented mice, like human subjects with vitiligo, have a loss of contact hypersensitivity associated with a loss of pigment cells within the epidermis. In the mouse, loss of melanocytes is associated with a decrease in the population density of Ia + cells.     

Ratio of Langerhans cells to Thy-1+ dendritic epidermal cells in murine epidermis influences the intensity of contact hypersensitivity

We have initiated a series of studies in vivo to investigate the physiologic role of Langerhans cells and Thy-1+ dendritic epidermal cells in the development and regulation of contact hypersensitivity. The density of I-A+ Langerhans cells and Thy-1+ dendritic epidermal cells in ammonium thiocyanate-separated epidermal sheets was determined in ten strains of inbred mice using immunofluorescence microscopy with monoclonal anti-I-A and anti-Thy-1 antibodies. Mice of different inbred strains were sensitized by painting the left ear with varying doses of either oxazolone or trinitrochlorobenzene. From five to 20 days after sensitization, groups of mice were challenged with the relevant antigen and the intensity of contact hypersensitivity, as measured by ear swelling, was determined. We then determined whether the intensity and/or duration of contact hypersensitivity in different strains of mice was influenced by the density of Thy-1+ dendritic epidermal cells or the ratio of I-A+ Langerhans cells to Thy-1+ dendritic epidermal cells. We found that there was marked variability in the density of Thy-1+ dendritic epidermal cells and I-A+ Langerhans cells in the ten strains of mice studied. The ratio of I-A+ Langerhans cells to Thy-1+ dendritic epidermal cells ranged from 0.5 in C57BL/10J mice to greater than 22 in A/J and BALB/cByJ mice. When small amounts of contact sensitizers were used to induce contact hypersensitivity (e.g., 20 micrograms of oxazolone or trinitrochlorobenzene), there was consistent strain variability in the intensity of ear swelling. There was a significant correlation between the ratio of I-A+ Langerhans cells to Thy-1+ dendritic epidermal cells and the intensity of contact hypersensitivity (Pearson's correlation coefficient 0.85, p = 0.002). Strains with the highest ratios of I-A+ Langerhans cells to Thy-1+ dendritic epidermal cells had the most ear swelling. There were no consistent differences in the duration of contact hypersensitivity observed among the ten different strains. Our results indicate that Thy-1+ dendritic epidermal cells may play a physiologic role in down-regulating contact hypersensitivity in vivo.     

Epidermal Langerhans' cells in chronic eczematous dermatitis of the palms treated with PUVA and UVB

Epidermal Langerhans' cells (LC) were studied in patients with chronic eczematous dermatitis of the palms. The monoclonal antibodies anti-Leu 6 and anti-HLA-DR were used, and the cells visualized with an immunoperoxidase technique. Increased numbers of LC were found in allergic contact dermatitis as well as in irritant contact dermatitis and hyperkeratotic dermatitis of the palms. The increased number of epidermal LC in lesional skin may facilitate presentation of exogenous or endogenous antigens to activated T-cells. One hand was treated with PUVA or UVB and the other hand served as a non-exposed control. PUVA treatment cleared the dermatitis and the LC number decreased markedly. With UVB treatment clinical improvement was achieved, and a less pronounced decrease in epidermal LC was noticed. There seems to be a crude relationship between the extent of clinical improvement and the reduction in epidermal LC numbers. The change in LC might be a primary event or secondary to a reduction of the inflammatory process.     

Studies on the effects of a high dose UVA-1 radiation therapy on surface markers and function of epidermal Langerhans cells

Recently, high-dose UVA-1 therapy (340–400 nm) was introduced as an effective treatment of severe exacerbated atopic dermatitis. Since the target of this type of radiation in the skin is not known we investigated using the mouse model whether surface markers of the antigen-presenting function of epidermal Langerhans cells are affected by UVA-1 radiation. Even repeated high doses of UVA-1 radiation (up to 50 J/cm²) had no detectable effect on surface ATPase activity and Ia antigen expression on Langerhans cells. Also, the contact allergen oxazolone was presented normally in skin treated with UVA-1 radiation. In contrast, if the mice were injected 1 h before irradiation with 8-methoxypsoralen a dramatic reduction in ATPase activity and Ia antigen expression on Langerhans cells was observed and the induction of contact sensitivity was suppressed (PUVA effect). These results show that epidermal Langerhans cells are not impaired either in structure or function and that these cells probably do not represent the primary target of UVA-1 radiation in the skin. No side effects resulting from a diminished Langerhans cell function should result from high-dose UVA-1 therapy.     

Deleterious effects of cis-urocanic acid and UVB radiation on Langerhans cells and on induction of contact hypersensitivity are mediated by tumor necrosis factor-alpha.

Ultraviolet B (UVB) light disrupts epidermal Langerhans cells (LC) universally and impairs the induction of contact hypersensitivity (CH) to epicutaneously applied haptens in certain strains of mice. Similar effects are observed when tumor necrosis factor-alpha (TNF alpha) is injected intradermally (ID) in mice. Trans-urocanic acid (UCA), a photoreceptor for UVB radiation, is known to be immunosuppressive. To determine whether cis-UCA is important in the process by which UVB and/or TNF alpha act in the skin, cis-UCA was injected ID into C57BL/6, C3H/HeN, BALB/c, and C3H/HeJ mice. Whole mounts of epidermis were removed 5 h later and stained immunochemically with anti-Ia antibodies. Microscopy revealed that Ia-bearing LC had lost their dendrites, had rounded up, and were reduced in number in all strains examined. Moreover, when dinitrofluorobenzene (DNFB) was applied epicutaneously to the injected site, induction of CH was grossly impaired. When neutralizing anti-TNF alpha antibodies were administered intraperitoneally 2 h prior to ID injection of cis-UCA, the deleterious effects on LC and CH induction were largely reversed. These results indicate that the actions of cis-UCA on LC and on CH induction are very similar to those achieved by ID injections of TNF alpha and by cutaneous exposure to low-dose UVB. Because the effects of UVB radiation and cis-UCA are reversed by anti-TNF alpha antibodies, we propose that UVB radiation impairs the induction of CH in mice by converting trans-UCA to cis-UCA within the epidermis; cis-UCA in turn causes the local release of TNF alpha, which thwarts sensitization by its ability to alter the functional program of epidermal Langerhans cells, thereby preventing the induction of CH.     

Effects of ultraviolet radiation on murine epidermal Langerhans cells: doses of ultraviolet radiation that modulate ICAM-1 (CD54) expression and inhibit Langerhans cell function cause delayed cytotoxicity in vitro.

Low doses (100 J/m2) of ultraviolet B (UVB) radiation from sunlamp fluorescent FS20 tubes inhibit the ability of freshly isolated murine epidermal Langerhans cells (LC) to support anti-CD3 MoAb-induced T-cell mitogenesis and selectively inhibit the upregulation of ICAM-1 expression by LC without causing appreciable cytotoxicity in short-term (less than or equal to 24 h) incubations (J Immunol 146:3347-3355, 1991). In the present study, epidermal cells (EC) were exposed to UVB radiation or were sham-irradiated and cultured for 24, 48, or 72 h when LC were recovered, enumerated, and assayed for simultaneous expression of I-A antigens and ICAM-1 by flow cytometry. UVB-irradiated LC that had been cultured for 24 h exhibited levels of I-A antigens comparable to those on unirradiated LC but expressed substantially less ICAM-1. After 48 and 72 h, cultured UVB-irradiated LC expressed somewhat lower levels of I-A antigens and markedly less ICAM-1 than unirradiated controls. Although similar numbers of LC were recovered from cultures initiated with UVB-irradiated and unirradiated epidermal cells after 24 h, far fewer identifiable LC were recovered from cultures seeded with irradiated cells at 48 and 72 h (approximately 50 and approximately 10% of control, respectively). The effect of UVB radiation on the survival of LC in vitro was not reversible with exogenous TNF alpha (125 U/ml) alone or granulocyte/macrophage colony-stimulating factor (5 ng/ml) and IL-1 (50 U/ml) in combination, although these cytokines had modest effects on the expression of I-A antigens and ICAM-1 by cultured UVB-irradiated LC. Results of survival studies performed with enriched LC preparations demonstrated that UVB radiation was clearly cytotoxic for LC and did not merely downregulate surface expression of I-A antigens or alter LC buoyant density. Exposure of LC to radiation from blacklight fluorescent (UVA) tubes (0.25 J/cm2) in the presence of 8-methoxypsoralen (1 micrograms/ml; PUVA) or monochromatic UVC radiation (20 J/m2) also inhibited LC accessory cell function. Results of survival studies performed with EC that had been exposed to PUVA or UVC radiation before culture were similar to those of studies performed with UVB-irradiated cells, although PUVA- and UVC-induced LC cytotoxicity was much more pronounced 48 h after culture initiation than UVB-induced cytotoxicity. UVA radiation alone augmented LC recovery at 24 and 48 h, but did not influence I-A antigen or ICAM-1 expression.(ABSTRACT TRUNCATED AT 400 WORDS)     

Distorted antigen-presenting function of Langerhans cells induced by tumor necrosis factor alpha via a mechanism that appears different from that induced by ultraviolet B radiation

Tumor necrosis factor alpha (TNF alpha) has been shown to mimic 2 effects of ultraviolet B (UVB) radiation in mice: morphologic damage to epidermal Langerhans cells (LC) and the inability to mount a normal contact hypersensitivity (CH) response. Our previous studies have shown LC to be the target of the immune tolerance evoked by UVB radiation, both during induction of CH in vivo and during presentation of protein antigen to CD4+ Th1 cells (Th1) in vitro. To determine whether these influences of TNF alpha and of UVB radiation on LC are related, 2 sets of experiments were performed. We first examined the effect of recombinant TNF alpha on the capacity of epidermal cells enriched for LC (IEC) to present keyhole limpet hemocyanin (KLH) to KLH-specific and Iad-restricted Th1. Addition of TNF alpha to co-cultures of IEC and Th1 significantly reduced proliferation in a dose-dependent manner. This inhibition was specific since it was reversed by neutralizing Ab against TNF alpha. That TNF alpha blocked Th1 proliferation by acting directly on LC is supported by 2 findings: 1) selective treatment of IEC prior to co-culturing also led to failure to present KLH; and 2) TNF alpha did not reduce Th1 proliferation stimulated by phorbol myristate acetate plus ionomycin, or by IL-2. We next examined the capacity of anti-TNF alpha Ab to protect LC from loss of antigen-presenting cell (APC) function induced by a single dose of 200 J/m2 UVB. Anti-TNF alpha Ab tested over a broad dose range did not prevent or restore the ability of UVB-irradiated IEC to present KLH to Th1.(ABSTRACT TRUNCATED AT 250 WORDS)     

UVB and UVC, but not UVA, potently induce the appearance of T6- DR+ antigen-presenting cells in human epidermis

Non-Langerhans cell, antigen-presenting T6- DR+ epidermal cells (EC) appear 3 days following broad band ultraviolet radiation exposure of human skin and are responsible for the increased antigen presentation capacity of EC seen 3 days after UV exposure. To determine the UV wavelengths that induce T6- DR+ EC, volar forearm skin of 10 human volunteers was irradiated in vivo with 4 minimal erythema doses (MED) each of pure UVA (mean 482 J cm-2), UVB (mean 0.390 J cm-2), and UVC (mean 0.397 J cm-2). The purity of the light sources was as follows: UVB, 98% of the emission was in the UVB range; UVC, 97% of the irradiance was in the UVC range; UVA, 100% of the energy had wavelengths longer than 340 nm. Three days after UV irradiation with 4 MED of each wavelength band, suction blister-derived EC suspensions were prepared from the UV-exposed and unirradiated sites. Percentages of T6+ DR+ Langerhans cells (LC) and T6- DR+ EC were quantitated. Relative to control EC, which contained 2.4 +/- 0.3% T6+ DR+ LC, the mean percentage (+/- SEM) of T6+ DR+ LC contained within UV-exposed EC was significantly decreased as follows: UVB, 0.5 +/- 0.2%; UVC, 0.9 +/- 0.1%; UVA, 0.5 +/- 0.2% (n = 10). T6- DR+ EC, absent in control EC, were induced both by UVB, 5.2 +/- 1.7% and UVC; 1.5 +/- 0.4%. Despite the use of more than 1200 times greater doses in J cm-2 of UVA than UVB and UVC, UVA was a poor inducer of T6- DR+ EC (0.5 +/- 0.2%) and in about half of these individuals, T6- DR+ EC were undetectable. The UV wavelengths for induction of T6- DR+ EC lies predominantly within the UVB band, but also to a lesser extent within the UVC band. These wavelengths appear to be analogous to both the wavelengths for generation of increased host susceptibility to UV-induced murine tumors and to the wavelengths for UV-induced systemic suppression of contact hypersensitivity. However, our data indicate that UV wavelengths for decreasing the number of T6+ DR+ LC in humans differs from the wavelengths for induction of systemic suppression of contact hypersensitivity in mice. Taken together, these data suggest that the appearance of T6- DR+ EC, but not the disappearance of T6+ DR+ LC, following UV exposure may be related to the induction of such antigen-specific suppressor T cells.     

IL-3 production as an in vitro marker of the genetically determined traits of UVB susceptibility and UVB resistance.

The capacity of low-dose ultraviolet B (UVB) radiation to disrupt epidermal Langerhans cell function and to prevent the induction of contact hypersensitivity (CH) is genetically determined in mice and men. In mice, Tnf alpha and Lps are the genetic loci at which reside alleles that dictate susceptibility and resistance to the deleterious effect of UVB radiation. Detection of the UVB-susceptibility (UVB-S) and UVB-resistance (UVB-R) traits relies upon the in vivo end point of contact hypersensitivity, and is cumbersome, labor intensive, and time consuming. It has recently been reported that hapten-immune murine T cells can secrete interleukin-3 (IL-3) in vitro when exposed to hapten-derivatized syngeneic stimulator cells. To determine whether this assay might be useful in distinguishing UVB-R from UVB-S mice, panels of UVB-susceptible (C57BL/10, C3H/HeN) and UVB-resistant (A/J, BALB/c, C3H/HeJ) mice were sensitized epicutaneously with dinitrofluorobenzene (DNFB). When challenged in vitro 6 d later with dinitrophenyl-derivatized stimulator cells, T cells from all strains proliferated and secreted IL-3. Moreover, T cells from UVB-R mice that were sensitized through UVB-treated skin also made copious amounts of IL-3. However, T cells from UVB-S mice whose abdominal skin had been UVB irradiated prior to epicutaneous application of DNFB failed to secrete IL-3 in vitro, although the cells did proliferate. We conclude that following application of a sensitizing dose of hapten to UVB-exposed skin of UVB-S mice a) hapten-specific T cells are selectively unable to secrete IL-3 in vitro in response to hapten stimulation, and b) this inability is a reliable marker of the UVB-S trait. The IL-3 assay may prove useful in elucidating the mechanism by which UVB-exposed Langerhans cells activate regulatory T cells, and in detecting the UVB-S and UVB-R traits in humans.     

Disparate effects of in vitro low-dose UVB irradiation on intravenous immunization with purified epidermal cell subpopulations for the induction of contact hypersensitivity

Low-dose ultraviolet (UV) B irradiation suppresses contact hypersensitivity (CH) reactions and alters the antigen-presenting function of epidermal cells (EC) in mice. To identify the EC sources of immunosuppression in this system, we examined the effect of UVB on the capacity of EC to induce and to regulate CH to trinitrochlorobenzene (TNCB). On day 0, cell sorter-purified populations of Ia+EC, Thy-1+EC, or Ia-/Thy-1-EC from CBA and C3H/HeJ mice were exposed to 200 J/m2 UVB from unfiltered FS20 Sunlamps, derivatized with hapten, and inoculated intravenously into syngeneic mice (5000 cells per inoculum). After 6 d, responsiveness was tested by challenging the left ear with 2% TNCB and measuring ear swelling responses. On day 14, regulation was tested by painting 7% TNCB on abdominal skin; after 6 d the right ear was challenged. Whereas mice which received haptenated unirradiated Ia+EC exhibited full CH responses without down-regulation, mice inoculated with haptenated irradiated Ia+EC displayed significantly diminished primary responses and, on subsequent immunization, displayed down-regulation. On the other hand, panels of mice that received haptenated unirradiated Thy-1+EC, and haptenated irradiated Thy-1+EC both showed hyporesponsiveness as well as down-regulation. Intravenous immunization with haptenated unirradiated Ia-/Thy-1-EC or with haptenated irradiated Ia-/Thy-1-EC led in each instance to immunologically "null events." These findings indicate that UVB irradiation profoundly affected Ia+EC such that their capacity to sensitize for CH was not only abrogated, but that such treatment also resulted in down-regulation of CH responses. By contrast, the same phototreatment had no effect on the inherent property of Thy-1+EC to mediate down-regulation of CH. We conclude that Ia+EC are immunologically relevant targets of low-dose UVB radiation, and that two populations of irradiated EC, Ia+EC, and Thy-1+EC, have the potential to deliver down-regulatory signals in this model of immunosuppression.     

UVB radiation and DNFB skin painting induce suppressor cells universally in mice.

Ultraviolet radiation (UVR)3 from within the spectrum B (UVB) has the capacity to distort the induction of contact hypersensitivity (CH) in murine skin. A damaging effect of UVB on epidermal Langerhans cells (LC) appears to be universal in all genetically defined strains of mice tested. However, while UVB impairs the induction of CH in some strains of mice, it has no apparent effect on CH in others. Thus, a disparity exists between the effects of UVB on LC and on CH. This is a paradox because LC are generally regarded to serve as the antigen-presenting cells of the skin, placing them at the earliest stages of induction of CH. One possible explanation for this paradox has been that UVB-susceptible strains of mice may generate hapten-specific suppressor T cells, whereas their UVB-resistant counterparts may not, when their skin is treated with UVR and painted with haptens such as dinitrofluorobenzene (DNFB). This possibility was excluded by examining the capacity of UVR and hapten to generate suppressor T cells in several different inbred strains of mice. The results indicate that the induction of hapten-specific afferent T suppressor cells is a universal sequela to treatment of mice with UVB and hapten, irrespective of whether the mice display the phenotype of vigorous CH or not. Thus, the genetic basis of UVB-resistance does not reside in the ability of UVR to induce suppressor T cells. Rather, attention should now be focused on its ability to interrupt induction of effector mechanisms.     

Disappearance of epidermal Langerhans cells during PUVA therapy

The numbers and morphological appearance of epidermal Langerhans cells (LCs) were studied in twenty-five patients with psoriasis receiving treatment with 8-methoxypsoralen (8-MOP) and long wavelength UV irradiation (UV-A) (PUVA). After a single exposure, LCs showed loss of fine dendritic processes. Repeated treatments resulted in a reduction of the number of LCs from the mean pretreatment value of 713/mm² to less than 60/mm² after seven treatments. The number of LCs remained low while treatment continued for up to 4 weeks. This finding may explain the impaired contact hypersensitivity observed in patients with psoriasis receiving PUVA therapy.