Carcinogen-induced depletion of cutaneous Langerhans cells

The role of the epithelial sentinels, Langerhans cells and γδT cells, in oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) arises in the oral epithelium, a tissue in which immune surveillance is mediated by its primary resident leukocytes, Langerhans cells (LCs), and γδT cells. Under steady-state conditions, LCs and γδT cells play a critical role in maintaining oral mucosal homeostasis. As antigen-presenting cells of stratified epithelia, LCs respond to various challenges faced by the epithelium, orchestrating innate, and adaptive immune responses in order to resolve them. γδT cells also sense diverse epithelial insults and react rapidly through cytokine production and cytolytic activity. These epithelial sentinels are also considered to be the first leukocytes in the oral epithelium to encounter early carcinogenic events that have the potential of becoming OSCC. As evident in many malignancies, leukocyte populations help prevent cancer development although they also promote tumor progression. OSCC is no exception, as studies have reported both anti- and pro-tumor roles of LCs and γδT cells. In this review, we summarize the ontogeny of LCs and γδT cells in the oral epithelium and discuss their role in OSCC.

Early antitumor activity of oral Langerhans cells is compromised by a carcinogen

Early diagnosis of oral squamous cell carcinoma (OSCC) remains an unmet clinical need. Therefore, elucidating the initial events of OSCC preceding tumor development could benefit OSCC prognosis. Here, we define the Langerhans cells (LCs) of the tongue and demonstrate that LCs protect the epithelium from carcinogen-induced OSCC by rapidly priming αβT cells capable of eliminating γH2AX⁺ epithelial cells, whereas γδT and natural killer cells are dispensable. The carcinogen, however, dysregulates the epithelial resident mononuclear phagocytes, reducing LC frequencies, while dendritic cells (DCs), macrophages, and plasmacytoid DCs (pDCs) populate the epithelium. Single-cell RNA-sequencing analysis indicates that these newly differentiated cells display an immunosuppressive phenotype accompanied by an expansion of T regulatory (Treg) cells. Accumulation of the Treg cells was regulated, in part, by pDCs and precedes the formation of visible tumors. This suggests LCs play an early protective role during OSCC, yet the capacity of the carcinogen to dysregulate the differentiation of mononuclear phagocytes facilitates oral carcinogenesis.

Glutamate heteroreceptor complexes in the brain

The existence of mGluR, NMDAR, AMPAR and putative KAR heteroreceptor complexes in synaptic and extrasynaptic regions of brain glutamate synapses represents a major integrative mechanism. Our aim in the current article is to analyze if the formation of the different types glutamate hetereceptor complexes involves the contribution of triplet amino acid homologies (protriplets) in a postulated receptor interface based on the triplet puzzle theory. Seven main sets (lists) of receptor pairs in databases were used containing various sets (lists) of human receptor heteromers and nonheteromers obtained from the available scientific publications including the publically available GPCR-hetnet database. Brain mGluR1-mGluR5 and mGluR2-mGluR4 isoreceptor complexes were demonstrated with a predominant extrasynaptic localization at a post- and prejunctional localization. The existence of putative mGluR4-mGluR7 heteroreceptor complexes in the basal ganglia is proposed. Metabotropic glutamate receptor subtypes also participated in the formation of a large number of heteroreceptor complexes like mGluR1-A1R, mGluR5-A2AR, mGluR5-D2R and D2R-A2AR-mGluR5, located in relation to glutamate synapses, especially in the basal ganglia. A putative mGluR1-GABAB1/2 heterocomplex may also exist. NMDAR heteroreceptor complexes were also demonstrated as a fundamental integrative mechanism in the glutamate synapse and its extrasynaptic membranes. It represented fundamental work on inter alia NMDAR-mGluR5, NMDAR-D1R and NMDAR-D2R heteroreceptor complexes involving both antagonistic and facilitatory allosteric receptor-receptor interactions. As to AMPA receptors, a heterocomplex was found for the interaction between IFNgR1 and the AMPAR mediated via the subunit GluA1 which may be of relevance for neuroinflammation. AMPAR-D2R heteroreceptor complexes were also demonstrated. Besides glutamate heteroreceptor complexes and their allosteric receptor-receptor interactions, a significant mechanism for the functional crosstalk can also be phosphorylation and/or reorganization of adapter proteins with dynamic binding to the two receptors modulating the allosteric receptor mechanism.

Photodynamic therapy with 5-aminolevulinic acid and diamino acid derivatives of protoporphyrin IX reduces papillomas in mice without eliminating transformation into squamous cell carcinoma of the skin

Photodynamic therapy (PDT) is used to treat malignant and nonmalignant diseases. It is also used for cosmetological skin treatment. PDT is generally considered to have a low risk of carcinogenicity. However, instances of nonmalignant human tumors turning malignant have been linked to PDT. In this study, we used 5-aminolevulinic (ALA) acid and 3 water soluble photosensitizers-PP(Arg)(2), PP(Ser)(2)Arg(2), PP(Ala)(2)Arg(2), all diamino acid derivatives of protoporphyrin IX-to treat benign papillomas in FVB/N mice induced by 7,12-dimethylbenz(a)anthracene (DMBA)-12-O-tetradecanoyl-phorbol-13-acetate (TPA). Of these drugs, ALA and PP(Arg)(2) were found the most efficient. PDT reduced the number of papillomas, but with increasing effectiveness of the drugs, the risk of malignant transformation of the papillomas into squamous cell carcinomas increased. The underlying mechanisms are not clear and further investigations are needed.

Photobiological information obtained from XPA gene-deficient mice

The XPA gene-deficient mouse, an animal model of xeroderma pigmentosum (XP), develops enhanced photobiologic reactions including acute inflammation, immunosuppression and skin carcinogenesis, because of the defect in the excision repair of ultraviolet-induced DNA lesions. The results strongly suggest that nuclear DNA is an important chromophore to initiate acute and chronic skin damages. The model mouse is a useful experimental animal not only to investigate the mechanisms of photosensitivity in XP, but also to study physiological photobiology in humans, because photobiologic reactions are greatly intensified in this mouse.

DNA damage initiates photobiologic reactions in the skin

Ultraviolet (UV) radiation can induce acute and chronic photobiologic reactions in the absence of exogenous chromophores. Nuclear DNA is a major chromophore to initiate UV-induced physiologic reactions. The XPA-gene deficient mouse, an animal model of xeroderma pigmentosum, develops increased photobiologic reactions including acute inflammation, immunosuppression and skin cancers, because of the defect in the excision repair of UV-induced DNA lesions.

Hazardous air pollutants and asthma

Asthma has a high prevalence in the United States, and persons with asthma may be at added risk from the adverse effects of hazardous air pollutants (HAPs). Complex mixtures (fine particulate matter and tobacco smoke) have been associated with respiratory symptoms and hospital admissions for asthma. The toxic ingredients of these mixtures are HAPs, but whether ambient HAP exposures can induce asthma remains unclear. Certain HAPs are occupational asthmagens, whereas others may act as adjuncts during sensitization. HAPs may exacerbate asthma because, once sensitized, individuals can respond to remarkably low concentrations, and irritants lower the bronchoconstrictive threshold to respiratory antigens. Adverse responses after ambient exposures to complex mixtures often occur at concentrations below those producing effects in controlled human exposures to a single compound. In addition, certain HAPs that have been associated with asthma in occupational settings may interact with criteria pollutants in ambient air to exacerbate asthma. Based on these observations and past experience with 188 HAPs, a list of 19 compounds that could have the highest impact on the induction or exacerbation of asthma was developed. Nine additional compounds were identified that might exacerbate asthma based on their irritancy, respirability, or ability to react with biological macromolecules. Although the ambient levels of these 28 compounds are largely unknown, estimated exposures from emissions inventories and limited air monitoring suggest that aldehydes (especially acrolein and formaldehyde) and metals (especially nickel and chromium compounds) may have possible health risk indices sufficient for additional attention. Recommendations for research are presented regarding exposure monitoring and evaluation of biologic mechanisms controlling how these substances induce and exacerbate asthma.

Acquisition of immune function during the development of the Langerhans cell network in neonatal mice

The immunological function of the Langerhans cell (LC) network in neonatal skin was examined by defining the development of cutaneous immunity relative to the structure, phenotype and function of the epidermal LC network in neonatal, juvenile and adult mice. Analysis of epidermal sheets showed the presence of major histocompatibility complex (MHC) II+, multilectin receptor DEC-205- cells within the epidermis of 3-day-old mice; both cell density and DEC-205 expression increased until day 14. When visualized with antibodies directed at MHC II, the network was poorly formed in 3- and 7-day-old mice, as there was a lower cell density and poor MHC II expression on dendritic processes, compared to mice at day14. Application of a fluorescent antigen to 3-day-old mice revealed that the LC were inefficient in transporting antigen to the draining lymph node. There was an improvement at day 7 and by day 14 comparable numbers of antigen carrying cells were detected in the lymph nodes of 6-week-old mice. The reduced antigen carriage in 3- and 7-day-old mice correlated with a poor contact sensitivity response. This was not simply due to failure to present antigen, but development of immunosuppression, as transfer of T cells from adult mice that were previously treated with antigen when they were 3 days old, to adult recipients resulted in antigen specific immunosuppression. Analysis of CD80 and CD86 expression showed that LC from day 3 skin expressed CD80, but not CD86 and application of antigen through this skin was inefficient in upregulating CD86. These findings indicate that when the neonatal LC network is poorly developed it is functionally immature and antigen applied through this 'functionally immature network' results in antigen specific immunosuppression.

Carcinogen-induced inflammation and immunosuppression are enhanced in xeroderma pigmentosum group A model mice associated with hyperproduction of prostaglandin E2

Xeroderma pigmentosum group A (XPA) gene-deficient mice easily developed skin cancers by the application of topical chemical carcinogens as well as by UV irradiation. As certain chemical carcinogens have been shown to be immunosuppressive, we examined the inflammatory and immunosuppressive effects of dimethylbenz(a)anthracene (DMBA) on XPA mice. Compared with wild-type mice, XPA mice showed greater ear swelling and reduction of epidermal Langerhans cells after DMBA application. Topical application of DMBA impaired the induction of contact hypersensitivity, initiated either locally or at distant sites. These DMBA-induced local and systemic immunosuppressions were more greatly enhanced in XPA mice than in wild-type mice. DMBA application induced pronounced production of PGE(2), IL-10, and TNF-alpha in the skin of XPA mice. Treatment with indomethacin, a potent inhibitor of PG biosynthesis, inhibited DMBA-induced inflammation and local immunosuppression. In XPA mice, increased serum IL-10 was detected after DMBA treatment. Excess production of PGE(2), TNF-alpha, and IL-10 after DMBA application may be involved in the enhanced local and systemic immunosuppression in DMBA-treated XPA mice. Susceptibility to DMBA-induced skin tumors in XPA mice may be due to easy impairment of the immune system by DMBA in addition to a defect in the repair of DMBA-DNA adduct. Enhanced immunosuppression by chemical carcinogens as well as the mutagenicity of these mutagens might be associated with the high incidence of internal malignancies seen in XP patients. Moreover, these results supported the hypothesis that persistent DNA damage is a trigger for the production of immunoregulatory cytokines.

Vascular Endothelial Growth Factor Inhibits the Development of Dendritic Cells and Dramatically Affects the Differentiation of Multiple Hematopoietic Lineages In Vivo

Defective function of dendritic cells (DC) in cancer has been recently described and may represent one of the mechanisms of tumor evasion from immune system control. We have previously shown in vitro that vascular endothelial growth factor (VEGF), produced by almost all tumors, is one of the tumor-derived factors responsible for the defective function of these cells. In this study, we investigated whether in vivo infusion of recombinant VEGF could reproduce the observed DC dysfunction. Continuous VEGF infusion, at rates as low as 50 ng/h (resulting in serum VEGF concentrations of 120 to 160 pg/mL), resulted in a dramatic inhibition of dendritic cell development, associated with an increase in the production of B cells and immature Gr-1+ myeloid cells. Infusion of VEGF was associated with inhibition of the activity of the transcription factor NF-κB in bone marrow progenitor cells. Experiments in vitro showed that VEGF itself, and not factors released by VEGF-activated endothelial cells, affected polypotent stem cells resulting in the observed abnormal hematopoiesis. These data suggest that VEGF, at pathologically relevant concentrations in vivo, may exert effects on pluripotent stem cells that result in blocked DC development as well as affect many other hematopoietic lineages.

Vascular Endothelial Growth Factor Inhibits the Development of Dendritic Cells and Dramatically Affects the Differentiation of Multiple Hematopoietic Lineages In Vivo

Defective function of dendritic cells (DC) in cancer has been recently described and may represent one of the mechanisms of tumor evasion from immune system control. We have previously shown in vitro that vascular endothelial growth factor (VEGF), produced by almost all tumors, is one of the tumor-derived factors responsible for the defective function of these cells. In this study, we investigated whether in vivo infusion of recombinant VEGF could reproduce the observed DC dysfunction. Continuous VEGF infusion, at rates as low as 50 ng/h (resulting in serum VEGF concentrations of 120 to 160 pg/mL), resulted in a dramatic inhibition of dendritic cell development, associated with an increase in the production of B cells and immature Gr-1+ myeloid cells. Infusion of VEGF was associated with inhibition of the activity of the transcription factor NF-κB in bone marrow progenitor cells. Experiments in vitro showed that VEGF itself, and not factors released by VEGF-activated endothelial cells, affected polypotent stem cells resulting in the observed abnormal hematopoiesis. These data suggest that VEGF, at pathologically relevant concentrations in vivo, may exert effects on pluripotent stem cells that result in blocked DC development as well as affect many other hematopoietic lineages.

Defective Function of Langerhans Cells in Tumor-Bearing Animals Is the Result of Defective Maturation from Hemopoietic Progenitors

Langerhans cells (LC), the APCs in the skin, serve as a model for investigation of dendritic cell (DC) function in tissues. DC play a crucial role in the generation of antitumor immune responses. In this study, we investigated the effect of the presence of tumor in vivo on the ability of LC to take up Ag, migrate to draining lymph nodes, and stimulate primary T cell responses. In two animal models, these functions were substantially inhibited. This effect was not restricted to LC located in the skin near a tumor but was also seen at sites distant from the tumor. The duration of tumor exposure, and not its ultimate size, were found to be important, suggesting that tumors could be inhibiting the maturation of LC rather than directly inhibiting their function. Model experiments with radiation chimeras supported this hypothesis. To investigate the potential role of vascular endothelial growth factor (VEGF) in these effects we used anti-VEGF-neutralizing Ab to treat animals bearing tumors. Treatment with the Ab at a dose of 10 μg i.p. per mouse, twice a week for 4 wk, significantly improved the number and function of LC as measured by their ability to migrate to lymph nodes and stimulate primary T cell responses, even at doses that do not affect the growth of these established poorly immunogenic tumors. Thus, inhibition of VEGF signaling may improve DC function in tumor-bearing hosts and possibly serve to improve the efficacy of cancer immunotherapy.

Induction of peripheral tolerance in neonatally thymectomized mice by immunization through chemical carcinogen-altered skin

BALB/c mice thymectomized 3 days after birth (3dnTx) are prone to the development of autoimmune gastritis. As this outcome may be a consequence of altered immunoregulatory mechanisms, we set out to determine the immunological status of these mice and their capacity to acquire antigen-specific peripheral tolerance. The latter was assessed by the capacity of these mice to suppress a contact sensitivity response to 2,4,6-trinitrochlorobenzene (TNCB) following treatment of the skin by the carcinogen, DMBA. The 3dnTx mice had a reduced number of CD4(+) and CD8(+) T cells and a reduced lymphocyte proliferative response to PHA, but a normal contact sensitivity response to TNCB. After treatment of the skin with DMBA these mice failed to develop contact sensitivity to TNCB. Adoptive transfer of splenocytes from these mice to naive mice transfered antigen-specific suppression, irrespective of whether the 3dnTx mice had developed autoimmune gastritis. We conclude that despite thymectomy at day 3 and the attendant immunosuppression, the capacity of BALB/c mice to generate antigen-specific peripheral tolerance to TNCB was retained. These results suggest that precursor T cells which mediate suppression to antigens such as TNCB are present in 3dnTx mice and that these cells are likely to have developed in the thymus and exported to the periphery before 3 days after birth.

Failure of carcinogen-altered dendritic cells to initiate T cell proliferation is associated with reduced IL-1 beta secretion

The activation of T cells through presentation of antigen by dendritic cells (DC) relies on many factors, including the correct balance of cytokines in the immediate microenvironment. Antigen presentation by DC migrating from carcinogen-treated skin is impaired as evidenced by the failure of antigen-pulsed DC to initiate specific T cell proliferation. To elucidate mechanism(s) of DC dysfunction, DC migrating from carcinogen-treated skin were collected, pulsed with OVA, and cultured with antigen-specific autologous lymphocytes. Supernatants were assayed for the costimulatory cytokine IL-1 beta which influences the outcome of DC:T cell interactions. The dendritic cells migrating from carcinogen-treated skin that failed to induce T cell proliferation were unable to produce IL-1 beta. This may account for the abrogation of DC function following exposure to chemical carcinogens and provides an explanation for the inability of DC to induce a protective immune response to carcinogen-induced tumours.

Physiology and pathophysiology of dendritic cells

Dendritic cells are antigen-presenting cells derived from the hematopoietic stem cell. The dendritic cell family includes Langerhans' cells (CD1a-positive dendritic cells of the skin), and antigen-presenting cells that are found in the lymphoreticular system and throughout the organ parenchyme. Dendritic cells play a key role in both the primary and secondary immune responses. Several studies indicate that these cells participate in antitumor immunity, tumor surveillance, graft-versus-host disease, and in the pathogenesis of clinical syndromes of unknown origin or those induced by viruses, such as the human immunodeficiency virus. Different disorders are characterized by an abnormal proliferation and accumulation of dendritic cells; for example, the Langerhans' histiocytes, which accumulate in Langerhans' cell histiocytosis. In this review the immunophenotypic, morphological, and functional characteristics of the dendritic cell family is described. The clinical and laboratory studies suggesting a unique role for these cells in various syndromes and diseases are reviewed. The Langerhans' cell histiocytoses and the malignant disorders associated with transformation of cells belonging to the dendritic cell family, are discussed.

Evaluation of a possible association of urban air toxics and asthma

The prevalence of asthma, measured either as the frequency of hospital admissions or number of deaths attributed to asthma, has increased over the last 15 to 20 years. Rapid increases in disease prevalence are more likely to be attributable to environmental than genetic factors. Inferring from past associations between air pollution and asthma, it is feasible that changes in the ambient environment could contribute to this increase in morbidity and mortality. Scientific evaluation of the links between air pollution and the exacerbation of asthma is incomplete, however. Currently, criteria pollutants [SOx, NOx, O3, CO, Pb, particulate matter (PM10)] and other risk factors (exposure to environmental tobacco smoke, volatile organic compounds, etc.) are constantly being evaluated as to their possible contributions to this situation. Data from these studies suggest that increases in respiratory disease are associated with exposures to ambient concentrations of particulate and gaseous pollutants. Similarly, exposure to environmental tobacco smoke, also a mixture of particulate and gaseous air toxics, has been associated with an increase in asthma among children. In addition, current associations of adverse health effects with existing pollution measurements are often noted at concentrations below those that produce effects in controlled animal and human exposures to each pollutant alone. These findings imply that adverse responses are augmented when persons are exposed to irritant mixtures of particles and gases and that current measurements of air pollution are, in part, indirect in that the concentrations of criteria pollutants are acting as surrogates of our exposure to a complex mixture. Other irritant air pollutants, including certain urban air toxics, are associated with asthma in occupational settings and may interact with criteria pollutants in ambient air to exacerbate asthma. An evaluation of dose-response information for urban air toxics and biological feasibility as possible contributors to asthma is therefore needed. However, this evaluation is compounded by a lack of information on the concentrations of these compounds in the ambient air and their effects on asthma morbidity and mortality. Through an initial review of the current toxicological literature, we propose a tentative list of 30 compounds that could have the highest impact on asthma and respiratory health. These compounds were selected based on their ability to induce or exacerbate asthma in occupational and nonoccupational settings, their allergic potential and ability to react with biological macromolecules, and lastly, their ability to irritate the respiratory passages. We recommend better documentation of exposure to these compounds through routine air sampling and evaluation of total exposure and further evaluation of biological mechanisms through laboratory and epidemiological studies directed specifically at the role these substances play in the induction and exacerbation of asthma.

The role of tobacco in penile carcinoma

OBJECTIVE

To study the role of tobacco in squamous cell carcinoma of the penis.

SUBJECTS AND METHODS

The use of tobacco in the form of cigarettes, chewing tobacco and snuff was studied in a total of 503 patients and age-matched controls.

RESULTS

By multivariate analysis, a significant association was found between smoking (P = 0.002) or chewing tobacco (P < 0.001) and the use of snuff (P = 0.004) in patients with penile carcinoma as compared with controls. A dose-response relationship was observed for both smoking and chewing.

CONCLUSIONS

The use of tobacco is a significant risk factor for penile carcinoma, and the use of more than one form of tobacco increases this risk.

Tobacco smoke condensate cutaneous carcinogenesis: changes in Langerhans' cells and tumour regression

Tobacco smoke condensate was painted on the skin of BALB/c mice. It increased the density and changed the morphology of Langerhans' cells (LC). LC number in epidermal sheets of treated mice was significantly higher (1793 LC/mm2) than in controls (946 LC/mm2) (P < 0.0001) and remained elevated for 35 weeks. LC became less dendritic, or even rounded in shape, and smaller in size. The function of the morphologically altered LC was impaired when assessed by the contact hypersensitivity response. These changes were associated with skin tumour development in all treated mice. Ten weeks after stopping the TSC treatment, LC number in skin tumours and in skin around these lesions had not decreased, but significantly increased (P < 0.0001). During this period tumour regression occurred in 23% of tumours; the remaining tumours showed a 50% reduction in size. At 45 weeks, the LC number in epidermal sheets around skin papillomas was 2274 +/- 14.14/mm2 and in invasive squamous cell carcinomas was 2088 +/- 183/m2. This was associated with reversible changes in LC morphology, where cells became fully dendritic. This also correlated with lymphocytic infiltration into tumours, tumour necrosis, reduction in tumour size and/or tumour regression. It is concluded that the influx of normal LC into the skin tumours allowed the development of an immune response with tumour regression.

Retrovirus-induced immunosuppression via blocking of dendritic cell migration and down-regulation of adhesion molecules

Dendritic cells (DC) within tissues may acquire and process antigens, carry them into lymph nodes and cluster and activate T cells. The ability of DC to acquire antigen and to migrate to lymph nodes was estimated during murine retroviral infection caused by Rauscher leukaemia virus (RLV). A novel mechanism of inducing immunodeficiency has now been identified. In mice infected with RLV, DC failed to migrate into lymph nodes following exposure of the skin to the contact sensitizer, fluorescein isothiocyanate. RLV infection of a proportion of DC both in skin and lymph nodes, shown by semi-quantitative polymerase chain reaction (PCR) and down-regulation of expression of adhesion molecules (CD54 and CD44) on the surface of Langerhans' cells, may contribute to the described phenomenon. A failure of DC migration could be an important immunosuppressive mechanism of RLV infection in mice and we speculate on a similar role for DC in human immunodeficiency virus-1 (HIV-1) infection in humans.

The migration of Langerhans' cells into and out of lymph nodes draining normal, carcinogen and antigen-treated sheep skin

Epidermal Langerhans' cell (LC) migration to the regional lymph node and beyond into central lymph was examined in sheep following topical application of the complete chemical carcinogen 7,12-dimethylbenz(a)anthracene (DMBA) or the contact sensitizing antigen 2,4,6-trinitrochlorobenzene (TNCB). This was facilitated by cannulating previously constructed pseudoafferent lymphatic vessels draining the skin treated with these agents or alternatively, the efferent lymphatic vessel of the regional lymph node. Application of DMBA resulted in a biphasic increase in LC migration. There was an initial increase in LC migration at 25 h with the maximum response (3.6 x 10(7) LC/h) occurring approximately 5 days after DMBA treatment. In contrast, the contact sensitizing antigen TNCB caused enhanced LC migration within minutes of the application of antigen (3.3 x 10(6) LC/h) and peak migration at 8-12 h. Examination of efferent lymph cells from the regional lymph node after DMBA treatment showed uncharacteristically large numbers of LC traversing the lymph node. These LC migration patterns suggest different mechanisms may trigger the migration of LC from skin after the application of DMBA to those associated with the normal processes of antigen presentation.

Langerhans cell migration patterns from sheep skin following topical application of carcinogens

Application of tumour promoters or complete chemical carcinogens to skin alters the density and/or morphology of epidermal Langerhans cells (LC). To examine the hypothesis that these chemical carcinogens alter LC migration kinetics from the epidermis, pseudoafferent lymphatic vessels draining defined areas of carcinogen treated sheep skin were cannulated and the number of LC migrating enumerated using indirect immunofluorescence and flow cytometry. The complete carcinogen benzo[a]pyrene (BP) and the tumour promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) caused an immediate two to four-fold increase in the rate of LC migration, while the tumour initiator urethane did not alter LC migration. The antigenicity of the carcinogens utilized was assessed in contact hypersensitivity experiments in mice. BP and TPA were mildly antigenic whereas urethane failed to initiate a contact hypersensitivity response in sensitized mice. It is concluded that the initial increase in LC migration from skin following the application of the tumour promoter TPA and the complete carcinogen BP is partly due to LC recognizing these carcinogens as antigens.

Differential modulation of contact hypersensitivity and delayed hypersensitivity reactions by topical application of 12-O-tetradecanoylphorbol-13-acetate

Ear/footpad swelling following sensitization and challenge with 2,4-dinitrofluorobenzene (DNFB)/allogenic splenocytes (AS) were used to monitor the effects of 12-O-tetradecanoylphorbol-13-acetate (TPA) on contact hypersensitivity (CHS) and delayed hypersensitivity (DHS) reactions, respectively. Topical treatment of dorsal or ventral SENCAR mouse skin 4x with 2 micrograms of TPA prior to sensitization of dorsal skin with DNFB suppressed attempts to induce CHS by subsequent challenge with DNFB. The adoptive transfer of splenocytes isolated from mice pretreated on the dorsum with TPA prior to dorsal sensitization with DNFB inhibited the development of CHS to DNFB in recipient mice. Conversely, topical treatment with TPA prior to s.c. sensitization with AS neither suppressed subsequent attempts to induce DHS, nor resulted in the generation of a splenocyte population capable of suppressing DHS reactions in adoptive transfer studies. Thus, promoting doses of topically applied TPA has differential effects on CHS and DHS reactions.

Migration of Langerhans cells from carcinogen-treated sheep skin

To define the mechanism(s) of carcinogen depletion of Langerhans cells (LC) from skin, the migration of LC from the skin to the regional lymph node was examined in carcinogen-treated, antigen-treated, and control sheep. This was assessed by cannulation of afferent lymphatic vessels that drain the treated areas of skin or the efferent lymphatic draining the regional lymph node. Cells draining from test or control skin were continuously collected and enumerated by indirect immunofluorescence and flow cytometry using specific anti-CD1 monoclonal antibodies. There was a marked increase in the rate of LC migration in the 8 h following the application of the contact sensitizing antigen trinitrochlorobenzene (TNCB). The chemical carcinogen 7,12-dimethylbenz(a)anthracene (DMBA) triggered a tenfold-greater migration of LC compared with TNCB--with the peak response at 5 d. After DMBA treatment LC were also detected in the efferent lymph of the regional lymph node. It is concluded that the depletion of LC from carcinogen-treated skin is due to the increased LC migration and not carcinogen-induced cell death.

Acceptance of class II major histocompatibility complex disparate skin grafts associated with suppressor cells and elevated Langerhans cell numbers

Class II major histocompatibility complex (MHC) molecules are only present on Langerhans cells (LC) in normal murine epidermis. Depletion of this antigen with the chemical carcinogen dimethylbenzanthracene (DMBA) causes I-E disparate B10.A(2R) congenic tail skin to be accepted permanently when grafted onto B10.A(4R) recipients. Adoptive transfer of spleen cells from these recipients into naive syngeneic hosts inhibited the ability of the host mice to reject untreated B10.A(2R) tail skin grafts. Hence DMBA-treated LC depleted I-E disparate skin grafts activate suppressor cells which did not inhibit BALB/c mice from rejecting a B10.A(2R) tail skin graft. In contrast, the tobacco derived carcinogen benzo(a)pyrene (BP) increased the number of epidermal LC but had no effect on either class I or class II MHC disparate skin graft survival time. This confirms that the number of class II MHC-positive LC is critical for the initiation of skin graft rejection; when the threshold level is attained graft rejection proceeds at a maximal rate that cannot be enhanced by raising the number of LC. The tolerant skin grafts had increased numbers of LC; this was not observed in syngeneic grafts and therefore may be related to the active suppression of immunity.

Assessment by planimetry of Langerhans' cell density in penile epithelium with human papillomavirus infection: changes observed after topical treatment

Langerhans' cells could have an important role in the immune surveillance for the malignant transformation associated with certain viral infections. A planimetric study of Langerhans' cells was performed on epithelial sheets obtained from male and female patients who presented with human papillomavirus-induced condylomata. Preliminary epidemiological studies have indicated that after a human papillomavirus infection the risk of malignant transformation is higher in the cervix than in the penis. Our study was designed in such a way that the Langerhans' cell density observed in condylomata could be compared to that detected in adjacent normal areas from the same patients. The results showed that a highly significant decrease in Langerhans' cells occurred in male and female human papillomavirus infected genital tracts. In the penis the local treatment with 5-fluorouracil restored the normal Langerhans' cell density. The significance of these findings in relationship with malignant transformation is discussed.

Langerhans' cells in equine cutaneous papillomas and normal skin

Langerhans' cells (LC) were investigated immunohistochemically and electron microscopically in normal equine epidermis and 133 equine cutaneous papillomas experimentally induced in five 2-year-old Thoroughbred horses. Class II major histocompatibility complex antigen-positive dendritic LC were found in the normal epidermis and ultrastructurally had the characteristic Birbeck's granules. In the developing phase of the papillomas, LC were significantly decreased in number and size, indicative of a hypofunctional state. In the regressing phase of the papillomas, LC were markedly increased in number, especially at the epidermis-dermis junction. LC with long dendrites were rich in cytoplasm with well-developed cytoplasmic organelles, including Golgi apparatus, lysosomes, Birbeck's granules, and multivesicular bodies. These LC were hyperfunctional. An infiltration of many T lymphocytes was also observed at the epidermis-dermis junction.

Cepharanthine inhibits two-stage tumor promotion by 12-O-tetradecanoylphorbol 13-acetate and mezerein on skin tumor formation in mice initiated with 7,12-dimethylbenz[a]anthracene

Cepharanthine, isolated from Stephania cepharantha, is one of the bisbenzylisoquinoline-type alkaloids. We have found that it inhibits tumor promotion after topical application in two-stage carcinogenesis in mouse skin. Epidermal ornithine decarboxylase activities inhibited by topical application of cepharanthine, with an 5 micrograms/mouse) and mezerein (5 micrograms/mouse) were found to be inhibited by topical application of cepharanthine, with a ED50 of 1.2 mumol and 1.4 mumol respectively. These inhibitory effects of cepharanthine are considered to be related to its antitumor activity in two-stage carcinogenesis in mouse skin. Cell-mediated immunosuppression by TPA was unaffected by topical application of cepharanthine. A diet containing 0.005% cepharanthine (about 0.5 mg mouse-1 day-1) slightly suppressed the two-stage promotion of skin tumors by twice-weekly applications of 2.5 micrograms TPA for 2 weeks (first stage) followed by twice-weekly applications of 2.5 micrograms mezerein for 23 weeks (second stage) in ICR mice following initiation by 50 micrograms 7,12-dimethylbenz[a]anthracene. Oral administration of cepharanthine inhibits the tumor promotion in two-stage carcinogenesis in mouse skin.

A role for prostaglandins in the suppression of cutaneous cellular immunity and tumour development in benzo(a)pyrene- but not dimethylbenz(a)anthracene-treated mice

Prostaglandins have been implicated in the immune suppression associated with the development of some tumours. Application of the prostaglandin synthetase inhibitor indomethacin, to murine skin prior to treatment with the chemical carcinogens benzo(a)pyrene (BP) or 7,12 dimethylbenz(a)anthracene (DMBA), restored contact sensitivity responses to 2,4-dinitrofluorobenzene in BP- but not DMBA-treated mice. However, indomethacin failed to restore antibody responses in either group of mice. Prolonged treatment with BP or DMBA led to cutaneous tumour formation. Indomethacin was found to delay the onset and reduce the size of tumours in BP- but not DMBA-treated mice. It is proposed that prostaglandin-induced suppression of cellular cutaneous immunity may play a role in BP- but not DMBA-induced cutaneous carcinogenesis.

Induction of suppressor T cells and inhibition of contact hypersensitivity in mice by 12-O-tetradecanoylphorbol-13-acetate and its analogs

12-O-tetradecanoylphorbol-13-acetate (TPA) and its analogs were surveyed for their abilities to modify contact hypersensitivity (CHS) responses in SENCAR mice. Sensitization of dorsal skin with 2,4-dinitrofluorobenzene (DNFB) and subsequent challenge of the ear 5 d later resulted within 24 h in ear swelling and increased vascular permeability (as measured by the extravasation of Evans Blue dye). Treatment of dorsal or ventral skin with TPA 4 times (application made every 3 or 4 d) prior to sensitization on the dorsum inhibited subsequent induction of CHS by DNFB challenge. Maximum suppression of CHS required sensitization at the site of TPA treatment. Suppression occurred over a narrow dose range of TPA (0.1-1.0 micrograms), and qualitatively correlated with the tumor incidences scored in an initiation-promotion multistage skin carcinogenesis experiment. Multiple applications (4x) of the promoters phorbol-12,13-dibenzoate (10 micrograms) and mezerein (2 micrograms) also suppressed CHS, whereas the non-promoter phorbol (20 micrograms) and the first stage tumor promoter 4-O-methyl TPA (20 micrograms) had no effect. Adoptive transfer of splenocytes isolated from mice pre-treated with TPA prior to DNFB sensitization inhibited the development of CHS in recipient mice that were sensitized and challenged with DNFB, but not oxazolone. Splenocyte preparations depleted of T lymphocytes prior to transfer could not suppress CHS in recipient mice. Conversely, suppressive activity was concentrated in splenocyte preparations depleted of adherent cells/monocytes. Collectively, these studies demonstrate that TPA treatment of murine epidermis prior to sensitization with hapten can inhibit subsequent hapten-dependent elicitation of CHS. This suppression is mediated in part by antigen-specific suppressor T cells. Furthermore, there is a qualitative correlation between the complete and second stage in vivo tumor-promoting activities of TPA and its analogs, and their abilities to inhibit CHS.

Indomethacin inhibits the chemical carcinogen benzo(a)pyrene but not dimethylbenz(a)anthracene from altering Langerhans cell distribution and morphology

Treatment of murine skin with the polyaromatic hydrocarbon carcinogens benzo(a)pyrene (BP) or dimethylbenz(a)anthracene (DMBA) for 3 weeks resulted in an increase and a decrease in epidermal Langerhans cell (LC) numbers, respectively, compared with solvent-treated skin. Implantation of subcutaneous indomethacin pellets prior to carcinogen treatment prevented the changes in LC numbers and morphology in BP, but not DMBA-treated skin. Indomethacin treatment was also found to reduce elevated prostaglandin E2 (PGE)2 levels in the skin of BP-treated mice, whereas PGE2 levels were not significantly raised in DMBA-treated mice. There thus appears to be a link between altered prostaglandin levels and LC numbers in murine skin treated with BP, but not DMBA. In the latter, LC numbers were reduced by mechanisms not reversed by indomethacin. It is concluded that increased prostaglandin levels may contribute to the impairment of cutaneous immunity previously observed in BP-treated mice by altering LC density and morphology within the epidermis.

Langerhans cell depletion in gliotoxin-treated murine epidermis

Langerhans cells (LC) are dendritic antigen presenting cells of bone marrow origin which reside in the suprabasal layer of the epidermis. They express high concentrations of Class II MHC glycoproteins on their plasma membrane and transport cutaneous antigen to local lymph nodes for presentation to helper T cells. They are thus essential for the induction of cutaneous immunity. Gliotoxin is a member of the epipolythiodioxopiperazine (ETP) group of fungal metabolites, derived from the human pathogen Aspergillus fumigatus. It has been shown to have immunomodulating properties in vivo and in vitro, and has been proposed as a potential immunosuppressant for transplantation therapy. Epicutaneous application of gliotoxin reduced the numbers of epidermal LC by 30-35 per cent with an associated morphological change from highly dendritic to a more rounded form. Electron microscopic studies showed selective damage to LC at very low (nM) concentrations of gliotoxin, with no obvious effect on adjacent keratinocytes. LC numbers remained depleted for 13 weeks after initial treatment, suggesting that systemic suppression or prolonged retention of gliotoxin within the skin may play a role in its mechanism of action.

Immunophenotypic and cell cycle analysis of lymph node cells from dimethylbenzanthracene-treated mice

The chemical carcinogen 7, 12-dimethylbenz-(a)anthracene (DMBA) depletes Langerhans cells from murine epidermis. Application of contact sensitizers to DMBA-treated skin induces specific immunological tolerance due to a DMBA-resistant epidermal antigen presenting cell (APC) migrating to local lymph nodes where it presents antigen in a way which activates suppressor cells. As alterations in local lymph node lymphocytes may enhance the ability of the DMBA-resistant APC to activate suppressor cells, these cells were examined in DMBA-treated mice. Lymph nodes in DMBA-treated mice had normal morphology but were larger and contained increased numbers of lymphocytes. Cell cycle analysis revealed that these lymphocytes did not arise from division within the lymph node, suggesting alterations in homing properties of lymphocytes. Contact sensitizer applied to DMBA-treated skin did not increase lymphocyte division, possibly due to suppressor cell inhibition of the development of effector lymphocytes. DMBA treatment had no effect on B cells or Ia expression, but decreased levels of the T lymphocyte cell surface molecule Thy-1, and increased L3T4 and Lyt-2 as quantitated by flow cytofluorimetry. These changes could influence the development of immune responses as these T cell molecules are receptors involved in lymphocyte interactions.

Effect of TCDD on the density of Langerhans cells in murine skin

Tetrachlorodibenzo-p-dioxin (TCDD) is a prototype for a group of toxic polyhalogenated aromatic hydrocarbons. We have studied the effect of TCDD on skin, specifically the difference in cutaneous response of congenic haired (hr/+) and hairless (hr/hr) mice. Topical application of 0.6 microgram of TCDD induces epidermal hyperplasia/hyperkeratinization in the skin of hr/hr mice, but does not affect the epidermis of congenic hr/+ littermates. Suppression of various parameters of the immune response has been found to be another effect of TCDD exposure in experimental animals. In the present study, we investigated the effect of topical treatment with TCDD on the density of epidermal immune cells, the Langerhans cells (LC), in the skin of hr/hr and hr/+ mice. Results showed that TCDD-induced epidermal hyperplasia/hyperkeratinization in skin of hr/hr mice is accompanied by an increase in the density of LC. In the skin of hr/+ mice, in which TCDD exposure does not induce hyperplastic changes, LC densities are not affected. The increase in LC densities in TCDD-treated hr/hr mouse skin did not result in increased sensitivity of the skin to contact hypersensitization with dinitrofluorobenzene, as measured by changes in ear thickness. When hr/hr murine skin was grafted into skin of hr/+ mice and the entire dorsal skin (including the graft) treated with TCDD, LC were increased in the grafted skin, but not in the surrounding hr/+ skin. Conversly, when hr/+ murine skin was grafted into hr/hr mice and both treated with TCDD, there was no increase in the density of LC in the grafted hr/+ skin. Concomitant treatment of hairless mice with TCDD and with indomethacin did not affect the increase in the density of LC induced by TCDD treatment alone. These findings suggest that TCDD-induced epidermal changes in hr/hr murine skin involve production of factors which mediate the increase in epidermal LC.

Replacement of Langerhans cells in murine palate

Palates from C3H mice were implanted onto prepared graft beds in histocompatible F1 hybrid mice. Biopsies taken 1, 2, 4, 8, and 16 wk later were prepared to demonstrate Langerhans cells (LC) of C3H and F1 (host) origin. After 1 wk only occasional LC (all of C3H origin) were present. By 2 wk total LC numbers had increased to a level approximately 50% greater than in control (non-implanted) palate, with most of this increase due to C3H LC proliferation. From 4 through 16 wk total LC numbers were not significantly different from those of control palate. During weeks 2 through 16 the percentages of LC of F1 origin were 31, 70, 39, and 19% respectively. These results indicate an increased proliferation of C3H LC with an initial migration of F1 LC which stops as C3H LC numbers increase.

Differential effects of benzo[a]pyrene and dimethylbenz[a]-anthracene on Langerhans cell distribution and contact sensitization in murine epidermis

The exposure of murine skin to potent chemical carcinogens induced distinctive effects on the distribution of epidermal Langerhans cells (LC). Our previous finding that weekly applications of 7,12-dimethylbenz[a]anthracene deplete the numbers of adenosine triphosphatase (ATPase)-positive LC was extended to show that LC are also depleted on Ia and beta-glucuronidase staining. In contrast, application of the tobacco-derived carcinogen, benzo[a]pyrene (BP), caused a significant increase in Ia-positive LC density within 2 weeks and elevated levels were maintained for up to 6 months with continuous treatment. The tobacco-derived cocarcinogenic agent, catechol, also enhanced the numbers of epidermal LC. The LC in carcinogen treated epidermis were morphologically abnormal; after BP and catechol treatment LC appeared smaller with shorter dendrites, whereas in DMBA treated epidermis LC were enlarged with elongated dendrites. Application of the contact sensitizing agent, dinitrofluorobenzene, to skin treated with BP induced hyporesponsiveness rather than contact sensitivity upon subsequent antigen challenge. Hence, the function of the large number of morphologically altered LC in BP treated skin was impaired. We conclude that carcinogen-induced alterations of LC are associated with impaired immunocompetence, although different carcinogens probably operate via different mechanisms to induce such phenomena.

Epithelial dendritic cells in pathological human oral tissues

Epithelial dendritic cells (EDC) were examined in human oral tissues with non-specific keratosis, lichen planus and squamous cell carcinoma. Acetone-fixed frozen sections were stained using an indirect immunoperoxidase technique and monoclonal antibodies to the human CD1 thymocyte (OKT6) and HLA-DR antigens. Significantly more T6+ and DR+ EDC were present in lichen planus tissues than normal controls, tissues with non-specific keratosis and the epithelial overlying/adjacent to squamous cell carcinomas, the latter tissues having comparable numbers of both T6+ and DR+ EDC. By contrast, significantly fewer T6+ EDC and significantly more DR+ cells were present in the invasive epithelium of squamous cell carcinomas than the overlying/adjacent epithelium of carcinomas, the non-specific keratosis group and the normal tissues. 23-60% of pathological tissues had either focal or general DR+ reactivity in keratinocytes, but there was no correlation between the density of T6+ or DR+ EDC and the keratinocyte DR status of the tissues. The results suggest that immunological enhancement occurs in lichen planus and possibly immunological impairment may characterize invasive squamous cell carcinoma.

The fate of meshed allograft skin in burned patients using cyclosporin immunosuppression

Three patients with burns of 35%, 60% and 25% were treated with cyclosporin after the application of allograft skin. Biopsies of the allografts were taken at appropriate intervals. The drug was continued for 3 weeks, 3 months and 3 weeks respectively without ill-effects on the patients. The allografts survived during cyclosporin treatment but were rejected 12 days after cessation of treatment in Case 1 and 5-7 days in Case 2. In Case 3 where a meshed auto/allograft 'sandwich' technique was used, there was no visible evidence of rejection. It is likely that the allograft was replaced by a "creeping substitution" in the sandwich technique. The Langerhans cell is probably not solely responsible for allograft rejection.

Antigen presented in the local lymph node by cells from dimethylbenzanthracene-treated murine epidermis activates suppressor cells

Application to skin depleted of LC by treatment with the chemical carcinogen DMBA of a dose of contact sensitizer optimal for inducing contact sensitivity activates transferrable suppressor cells. Excision of solvent- or DMBA-treated skin at various times following application of the contact sensitizer DNFB indicated that the fraction of antigen which leaves the skin within the first few hours induces tolerance. An initial signal inducing unresponsiveness, observed within 1/2 hr, was overturned 3-6 hr later. A more permanent tolerogenic signal in the DMBA- but not solvent-treated lymph node resulted from an epidermal cell from DMBA-treated skin presenting antigen to suppressor cells. Therefore it is likely that suppressor cells are activated in DMBA-treated mice by an epidermal cell which migrates to the local lymph node. Local lymph node cells from DMBA-treated mice also have a diminished ability to present antigen in vivo but they do not activate suppressor cells.

Effect of cigarette smoking on cervical epithelial immunity: a mechanism for neoplastic change?

Langerhans' cells in cervical epithelium in colposcopic biopsy specimens were identified by immunocytochemical staining for S100 protein and T6 (CD1) antigen, and their density was quantified. Possible cofactors for the development of cervical neoplasia were examined for any effect on the cell counts per unit area. Current cigarette smoking was associated with a significant decrease in the Langerhans' cell population in both normal epithelium and lesions due to cervical intraepithelial neoplasia. Ex-smokers tended to have cell counts between those of smokers and non-smokers. There was a dose-response relation between number of cigarettes smoked daily and effect on cell counts. These findings of a local immunological effect of smoking on cervical epithelium may explain the means by which cigarette smoking contributes to the development of cervical neoplasia.

Ia+ epithelial dendritic cells during oral carcinogenesis in the rat

Epithelial dendritic cells (EDC) were examined during the induction and growth of oral squamous cell carcinomas in rats treated with the carcinogen 4-Nitroquinoline N-oxide (4NQO). Acetone-fixed frozen sections of the palate and tongue were stained using an indirect immunoperoxidase technique and a monoclonal antibody to rat Ia (MRC OX-6). After 6 months there was a significant increase in Ia+ EDC/mm2 in non-invasive palatal and lingual epithelium compared with untreated and solvent painted controls. Furthermore, after 9 months there were significantly more Ia+ EDC/mm2 in non-invasive lingual epithelium compared with invasive epithelium or the epithelium overlying/adjacent to squamous cell carcinomas of the tongue. Although there were no significant differences of Ia+ EDC/mm2 between infiltrating epithelium of lingual carcinomas and non-invasive epithelium overlying/adjacent to the tumour, these tissues did contain significantly more Ia+ EDC than lingual epithelium from either solvent-only or untreated controls. The results indicate that treatment with 4NQO stimulates an increase in Ia+ EDC numbers which, although remaining higher than in controls, is not maintained within, or adjacent to, sites of neoplastic change.

Suppressor cell activation and enhanced skin allograft survival after tumor promotor but not initiator induced depletion of cutaneous Langerhans cells

During chemical carcinogenesis Langerhans cells (LC) are depleted from the epidermis, disrupting the normal immunological functions of the skin. Tumor promotors but not initiators, have been shown to deplete adenosine triphosphatase (ATPase)-positive LC from the skin and therefore the cutaneous immune system may be impaired during tumor promotion but not initiation. The present study shows that the tumor promotor 12-O-tetradecanoylphorbol 13-acetate (TPA) but not the initiator urethane depletes Ia-positive LC from BALB/c murine ear epidermis, and beta-glucuronidase-positive LC from C57BL mouse tail skin. Sensitization with 2,4-dinitrofluorobenzene (DNFB) through urethane-treated skin resulted in a normal contact sensitivity response when the mice were challenged 5 days later. In contrast, tolerance resulted from sensitization through TPA-treated skin as a result of the generation of suppressor cells. In addition, TPA but not urethane-treated C57BL mouse tail skin survived for an extended time when grafted onto histoincompatible BALB/c mice. Therefore, impairment of the normal immunological functions of skin resulted from treatment with the tumor promotor TPA but not the tumor initiator urethane, which suggests that a loss of LC during tumor promotion may impair immunological protection against skin tumors.

Sensitization through carcinogen-induced Langerhans cell-deficient skin activates specific long-lived suppressor cells for both cellular and humoral immunity

Application of 2,4-dinitrofluorobenzene (DNFB) to BALB/c mouse skin depleted of epidermal Langerhans cells (LC) by the chemical carcinogen 7,12-dimethylbenz[a]anthracene (DMBA) activated cells which suppress both contact sensitivity and antibody production when transferred into naive host mice. Tolerance was induced by a concentration of DNFB optimal for inducing contact sensitivity in solvent-treated control mice. The cellular and humoral responses of hosts to a second antigen, 2,4,6-trinitrochlorobenzene (TNCB), were unaffected by these suppressor cells, demonstrating specificity for DNFB. Suppressor cells for cellular and humoral immunity could still be demonstrated 6 months following activation, by which time some mice had died, presumably of old age. The dose responses to sensitizer for generation of cells which suppressed contact sensitivity and antibody production differed, indicating that separate populations of suppressor cells probably inhibit these responses. Hence, during cutaneous chemical carcinogenesis, depletion of LC may allow activation of specific long-lived suppressor cells capable of inhibiting cellular or humoral antitumor immune responses.

Effects of low or high doses of short wavelength ultraviolet light (UVB) on Langerhans cells and skin allograft survival

Since Langerhans cells (LC) are normally the only cells within the epidermis to express the class II major histocompatibility complex (MHC) transplantation antigens, depletion of LC could be expected to prolong skin allograft survival by reducing the antigenic disparity between host and recipient. To assess this hypothesis, donor C57BL mouse shaved dorsal trunk or tail skin was exposed to high (200 mJ/cm2) or low (40 mJ/cm2) doses of short wavelength ultraviolet light (UVB) before grafting on to the thorax of BALB/c mouse recipients of the same sex. These strains have different major and minor transplantation antigens. The effects of UVB treatments on LC were determined by electronmicroscopy. Skin grafted 1-14 days following a single high dose of UVB irradiation was ultrastructurally depleted of LC and survived significantly longer than unirradiated skin before being rejected. After a 21-day interval between exposure and grafting when LC were again present in the epidermis there was no significant difference between treated and control graft survival. Exposure to low dose UVB irradiation only significantly increased graft survival for skin transplanted 1-3 days after irradiation; skin grafted 4 days following irradiation survived for a similar period to unirradiated control skin grafts. Electronmicroscopy showed that the low UVB dose did not deplete LC from the epidermis. We conclude that after low dose UVB treatment the class II MHC antigens on the LC plasma membrane were lost temporarily, thus prolonging graft survival, but when the plasma membrane antigens were re-expressed graft survival returned to normal.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term effects of local ionizing radiation treatment on Langerhans cells in mouse footpad epidermis

Langerhans cells (LC) were studied with ADPase histochemistry in sheets of hind footpad epidermis from groups of CBA/H mice. Single, local 20-Gy doses of 250-kV x-rays were administered to the right hind feet of the mice when they were 3-4 months old, and LC were counted at intervals ranging from 2 to 24 months later. In unirradiated mice, aged 5-19 months, the mean density of LC in footpad was 1521-1617 cells/mm2. It dropped to 1137 +/- 86 cells/mm2 (mean +/- SE) in untreated 28-month-old mice. At times from 2-15 months after irradiation, normal mean densities of LC were present in footpad epidermis. On average, LC numbers were subsequently reduced to 1078 +/- 65/mm2 by 19 months after irradiation (71% of the cells in age-matched controls) and to 789 +/- 53/mm2 by 24 months (59% of the cells in age-matched controls). Loss of cells was focal. Chronic radiation-induced fibrosis and damage to circulatory function in skin may have contributed to impaired replacement of LC from bone marrow precursors. The possibility that late radiation-related depletion of the LC population permits development of skin tumors as a delayed consequence of exposure to ionizing radiation is discussed.