Immunologic mechanisms in UV radiation carcinogenesis

Nitrogen mustard (mechlorethamine) and UVB photocarcinogenesis: a dose response effect

The effects of UVB energy and nitrogen mustard (mechlorethamine, HN2) on tumor formation in the hairless mouse skin was examined. Twice weekly applications of HN2 produced tumors in 34% of the mice. In addition, the HN2 treatments plus UVB radiation resulted in a significant acceleration in tumor formation as compared to either carcinogenic stimulus alone. The twice weekly application of HN2 plus UVB exposure was more tumorigenic than UVB plus HN2 applied once a week. Thus a positive carcinogenic dose response was noted. No tumor-suppressing effects were detected in this study.

Sun and malignant melanoma

The incidence and mortality rates of malignant melanoma in Caucasians are increasing rapidly in many countries worldwide. Considerable circumstantial evidence suggests that exposure to solar radiation may play a role in this substantial rise in malignant melanoma. This evidence comes primarily from epidemiologic studies and from the identification of susceptible phenotypes. Despite the increasing data that implicate sunlight as an important factor in the development of certain types of malignant melanomas in humans, the role of solar electromagnetic radiation in the pathogenesis of human malignant melanomas is yet to be determined.

Immunological unresponsiveness induced by ultraviolet radiation

Immunological unresponsiveness can be initiated by exposure of mice to UV radiation, followed by the introduction of certain antigens. These antigens include epicutaneously applied chemicals that induce contact hypersensitivity (CHS), and antigens that occur on skin cancers induced by UV radiation. Mice exposed repeatedly to high doses of UV radiation during UV carcinogenesis develop immunological unresponsiveness to UV radiation-induced skin cancers, which are highly antigenic. This unresponsiveness is associated with the appearance of suppressor T lymphocytes that are specific for tumors induced by UV radiation, even though these tumors express individually specific transplantation rejection antigens. Thus, the occurrence of suppressor cells with specificity for a set of non-cross-reacting tumors suggests that a common, UV-associated regulatory antigen or determinant may be present on UV-induced skin cancers. Suppression of CHS in mice by UV radiation can be induced by two different procedures. One involves applying the sensitizer directly on skin exposed to low doses of UV-B radiation and is thought to result from a direct effect of UV radiation on cutaneous Langerhans cells. The second involves application of the sensitizer to the unirradiated skin of mice or guinea pigs exposed several days earlier to a higher dose of UV-B radiation. The mechanism of the latter phenomenon is not well understood, but there is evidence that it results from an alteration of antigen presentation by splenic macrophages. Both forms of suppression are associated with the appearance of antigen-specific suppressor lymphocytes in the animals' spleens, which prevent the induction of CHS upon transfer to a normal recipient. Either or both of these pathways could be responsible for the formation of the suppressor cells involved in UV carcinogenesis. Recent studies suggest that UV radiation may also affect immunological responsiveness in humans as well as in animals. However, the extent of such alterations and the mechanisms by which they occur are still unknown.

Cancer, warts, and sunshine in renal transplant patients. A case-control study

94 renal transplant patients were examined for the presence of cutaneous malignancies, actinic keratoses, warts, and cutaneous fungal infection, and a history was taken of infection with herpes simplex and herpes zoster. Each patient had a control matched for age, sex, and sun exposure. Of the 17 patients with high exposure to sunshine (more than 3 months in a tropical or subtropical climate or more than 5 years in an outdoor occupation), 2 had squamous cell carcinoma and 7 actinic keratoses. These lesions did not occur in the other renal transplant patients or the control group. The immunosuppressive effect of ultraviolet radiation in the sunburn spectrum (290-320 nm) in man and animals may be related to the increased incidence of cutaneous malignancy, actinic keratoses, and warts. Transplant patients should be under regular surveillance for the early detection and treatment of premalignant cutaneous lesions, and they should receive advice on avoiding sun exposure.

Immunological surveillance of tumors in the context of major histocompatibility complex restriction of T cell function

The immunological surveillance hypothesis was formulated prior to the realization of the fact that an individual's effector T cells generally only see neoantigen if it is appropriately presented in the context of self MHC glycoproteins. The biological consequence of this mechanism is that T lymphocytes are focused onto modified cell-surface rather than onto free antigen. The discovery of MHC-restricted T cell recognition, and the realization that T cell-mediated immunity is of prime importance in promoting recovery from infectious processes, has thus changed the whole emphasis of the surveillance argument. Though the immunological surveillance hypothesis generated considerable discussion and many good experiments, there is no point in continuing the debate in the intellectual context that seemed reasonable in 1970. It is now much more sensible to think of "natural surveillance" and "T cell surveillance," without excluding the probability that these two systems have elements in common. We can now see that T cell surveillance probably operates well in some situations, but is quite ineffective in many others. Part of the reason for this may be that the host response selects tumor clones that are modified so as to be no longer recognized by cytotoxic T cells. The possibility that this reflects changes in MHC phenotype has been investigated, and found to be the case, for some experimental tumors. In this regard, it is worth remembering that many "mutations" in MHC genes that completely change the spectrum of T cell recognition are serologically silent. The availability of molecular probes for investigating the status of MHC genes in tumor cells, together with the capacity to develop cloned T cell lines, monoclonal antibodies to putative tumor antigens, and cell lines transfected with genes coding for these molecules, indicates how T cell surveillance may profitably be explored further in both experimental and human situations.

Multiple tumour-specific antigens expressed on a single tumour cell

Tumours induced by physical or chemical carcinogens often express tumour-specific antigens that can induce strong protective immune defence in the host. The diversity of these unique antigens among different tumours is seemingly endless, and has been compared to that of immune receptors. At present, the nature and complexity of this antigenicity is not known for any single tumour. Here we describe the unique antigenicity expressed by a murine ultraviolet light (UV)-induced fibrosarcoma. This tumour is clearly subject to immune surveillance by the normal host, and does not grow progressively unless it undergoes antigenic changes. Using defined monoclonal T-cell probes and tumour variants selected in vitro with these probes, we found that the total antigenicity consisted of multiple independent components, all of which were tumour-specific and expressed simultaneously on the same tumour cell. The demonstration of this antigenic complexity will enable us to identify and compare the molecular composition of the components of this antigen, as well as to determine their individual roles in tumour rejection and escape.

Ultraviolet light-induced suppression of antigen presentation

Ultraviolet (UV) light irradiation of animals results in the development of specific T suppressor cells that inhibit antitumor immune responses. It is thought that suppression may arise as a consequence of altered antigen presentation by UV-irradiated epidermal cells. This hypothesis is based on evidence demonstrating that specific lymphoid tissues from UV-irradiated hosts exhibit impaired antigen-presenting function and that animals cannot be contact sensitized when antigens are applied to a UV-irradiated skin site. Langerhans cells of the skin are likely candidates as targets of UV-induced defects in antigen presentation as they bear Fc and C3b receptors, express Ia antigens, are of bone marrow origin, and are capable of presenting antigen in vitro. We speculate on the possible clinical usefulness of UV-induced tolerance to specific antigens such as those encountered in monoclonal antibody therapy and tissue transplantation.

Suppressor mechanisms in tumor immunity

There are many parallels between T cell-mediated suppression of tumor immunity and suppression of immune responses to haptens and polypeptides. We propose a cell interaction model which takes this into account and outlines a regulatory pathway for suppression of immunity to tumor antigens. Free antigen or antigen/antibody complexes trigger an inducer T cell subset, Tsi, which is tumor-specific. This cell activates a non-immune T cell population, pre Tse, to generate effector suppressor cells, Tse. The Tse are specific for either the idiotype of Tsi or for antigen complexed with a soluble factor made by the Tsi, but the suppression they mediate is antigenically nonspecific. Tumor antigen-specific suppressor factors, TsF, play a major role in the communication between different suppressor cells. Characterization of polyclonal and monoclonal factors produced by Tsi, called TsFi, indicates that they both bind to tumor antigen and contain tumor-specific (idiotypic?) determinants.

The role of UVB radiation in the induction and elicitation of photocontact hypersensitivity to TCSA in the mouse

Photocontact hypersensitivity (PHS) to 3,3',4',5 tetrachlorosalicylanilide (TCSA) can be induced in mice by using cyclophosphamide as an immunopotentiator. Only UVA (320-400 nm) radiation was required for both sensitization and elicitation of PHS. The reaction was successfully transferred to syngeneic mice by injecting them with lymph node cells from sensitized donors, a finding that demonstrates the immunologic nature of PHS. The presence of UVB (280-320 nm) radiation was not necessary for sensitization and did not increase PHS beyond the levels observed with UVA radiation alone. Ultraviolet radiation in the UVB range (plus a small amount of UVA radiation) from FS40 sunlamps in the dose employed did not induce statistically significant PHS to TCSA, nor did it elicit a significant response in mice sensitized with TCSA plus UVA radiation. However, treatment of mice with UVB radiation at a distant site 6 days before sensitization suppressed the induction of PHS. This suppression appeared to be analogous to the systemic suppression of ordinary contact hypersensitivity in mice by UVB radiation.

An enzyme-linked immunosorbent assay (ELISA) for detergent solubilized Ia glycoproteins using nitrocellulose membrane discs

An enzyme-linked immunosorbent assay has been developed for the quantitative detection of detergent solubilized murine Ia. Nitrocellulose membrane discs were used to bind membrane glycoproteins applied in solutions containing detergent. The bound antigen was detected by monoclonal antibodies and horseradish-peroxidase-coupled anti-IgG. The assay produced a linear response with respect to antigen concentration, and could readily detect partially purified Ia derived from 10(3) to 10(4) mitogen stimulated spleen cells. Nitrocellulose discs efficiently bound protein in the presence of deoxycholate, taurocholate, and octylglucoside. Less binding occurred in the presence of Triton X-100 or Tween 80, but 90% binding efficiency was obtained in 0.01% solutions of these detergents. The association of protein with the discs was stable under normal conditions for antigen detection, but could be further stabilized by briefly fixing with glutaraldehyde for more rigorous procedures. The ability of this method to detect antigen in detergent solutions makes it useful in monitoring fractions during the purification of cell membrane proteins.

Reduction of Langerhans cells in human epidermis during PUVA therapy: a morphometric study

Skin biopsies were obtained before and after PUVA therapy from the normal skin of 5 psoriatic patients. By electron microscopic morphometric techniques the pretreatment volume density of Langerhans cells within the epidermis was estimated to be approximately 1%. This density was reduced in all 5 patients after therapy. The volume density of Langerhans cell granules per Langerhans cell cytoplasm was on an average 0.8% and this density was reduced in 4 of the patients after therapy, while in one patient there was an increase. There was a reduced volume density of Langerhans cell granules per unit volume of epidermis in all 5 patients after therapy. The mean length of the Langerhans cell disc was 260 +/- 120, nm the mean thickness 40 nm and the mean diameter of the Langerhans cell vesicle 120 +/- 30 nm. None of these parameters changed after PUVA therapy. The reduced volume density of Langerhans cells is discussed in the context of possible implications for immune reactions in the skin.