Heterogeneity of tumorigenicity phenotype in murine tumors. I. Characterization of regressor and progressor clones isolated from a nonmutagenized ultraviolet regressor tumor.

We have shown that both regressor and progressor clones can be isolated from a UV regressor tumor, RD-1024. Although the daughter clones are characterized by differences in tumorigenic potential in normal transplant hosts, they nevertheless seem to express the same major tumor rejection antigens, because immunization with either the regressor parent tumor, RD-1024, or with regressor Cl 8 protects against subsequent challenge with progressor C1 4 or Cl 9. Consistent with the in vivo-generated data is the evidence that draining lymph node cells with functional specificity for regressor Cl 8 are capable of cross-reactive cytotoxicity in an in vitro chromium release assay. We have demonstrated an indirect interaction occurring in vivo between regressor and progressor cells, in that Cl 8 cells have the ability to influence the outcome of simultaneous or sequential challenge with Cl 4 or Cl 9 cells. Because 500 rad of gamma irradiation has been shown to compromise the ability of mice to respond to a primary challenge with tumor, an immunological mechanism is implicated in the ultimate rejection of progressor tumor in a doubly challenged host. The importance of these results lies in the knowledge that these interacting subpopulations have been isolated directly from a tumor growing in vivo and that no selection pressure has been exerted on the cells greater than the short in vitro culture period necessary for the isolation and expansion of individual clones. The apparent immunoregulatory potential in a tumor-bearing animal is thus seen to be modified in accordance with the phenotypic heterogeneity of the cells within that tumor.

Platelet-derived growth factor is a potent biologic response modifier of T cells.

Freshly isolated lymph node (LN) cells cultured in serum-containing medium were restricted to produce primarily interleukin 2 (IL-2) subsequent to T cell activation. Only minimal amounts of IL-4, IL-5, or interferon gamma (IFN-gamma) were produced under these conditions. Similar populations of LN cells cultured in serum-free medium were able to produce a variety of lymphokines after T cell activation, with the relative quantities of each species being dependent upon the lymphoid organ source of the lymphocytes. A similar relationship in the patterns of lymphokines produced by activated T cell hybridomas maintained under serum-free conditions was also observed, whereas activation in serum-supplemented media resulted in a predominant restriction to the secretion of IL-2. Additional studies determined that the entity in serum responsible for restricting T cell function in vitro was platelet-derived growth factor (PDGF). The PDGF-BB isoform was established to be the most active in the regulation of T cell function, enhancing IL-2 while depressing the production of IL-4, IL-5, and IFN-gamma at concentrations below 1 ng/ml. PDGF-AB was also found to be quite active, however, this isoform of PDGF was incapable of influencing IFN-gamma production at the concentrations tested. PDGF-AA was very weakly active. It therefore appears that PDGF, acting primarily through a beta receptor subunit (either alpha/beta- or beta/beta-type receptors) is able to influence profoundly the behavior of T cells, with some of its modulatory effects exhibiting isoform specificity. This is reflected by an enhancement in the production of IL-2, while simultaneously depressing the secretion of IL-4, IL-5, and IFN-gamma (PDGF-BB only) after T cell activation. Kinetic studies, where cell supernatants were analyzed both 24 and 48 h after T cell activation, suggested that "desensitization" to PDGF influences can occur naturally in vitro. Those species of lymphokines that were inhibited by PDGF over the first 24 h after activation could be produced at normal levels over the subsequent 24-h period. Finally, lymphokines maintained in the presence of PDGF-BB for greater than 24 h before their activation lost sensitivity to this growth factor. These cells regained responsiveness to PDGF after an additional incubation period in PDGF-free medium. Collectively, our data imply that the pattern of T cell lymphokines produced, plus the kinetics of their production after activation, are being controlled by the potent serum growth factor PDGF.(ABSTRACT TRUNCATED AT 400 WORDS)

Regulation of murine lymphokine production in vivo. III. The lymphoid tissue microenvironment exerts regulatory influences over T helper cell function.

We investigated the capacity of murine T lymphocytes, isolated from various lymphoid organs of normal or antigen-primed donors, to produce IL-2 or IL-4 after activation with anti-CD3 or specific antigen. Our results established that T cells resident within lymphoid organs being drained by nonmucosal tissue sites (e.g., axillary, inguinal, brachial lymph nodes, or spleen) produced IL-2 as the predominant T cell growth factor (TCGF) after activation. Conversely, activated T cells from lymphoid organs being drained by mucosal tissues (Peyer's patches, and cervical, periaortic, and parathymic lymph nodes) produced IL-4 as the major species of TCGF. Analysis of the lymphoid tissues obtained from adoptive recipients of antigen-primed lymphocytes provided by syngeneic donors provided evidence that direct influences were being exerted on T cells during their residence within defined lymphoid compartments. These lymphoid tissue influences appeared to be responsible for altering the potential of resident T cells to produce distinct species of TCGF. Steroid hormones, known transcriptional enhancers and repressors of specific cellular genes, were implicated in the controlling mechanisms over TCGF production. Glucocorticoids (GCs) were found to exert a systemic effect on all recirculating T cells, evidenced by a marked dominance in IL-4 production by T cells obtained from all lymphoid organs of GC-treated mice, or after a direct exposure of normal lymphoid cells to GCs in vitro before cellular activation with T cell mitogens. Further, the androgen steroid DHEA appeared to be responsible for providing an epigenetic influence to T cells trafficking through peripheral lymphoid organs. This steroid influence resulted in an enhanced potential for IL-2 secretion after activation. Anatomic compartmentalization of the DHEA-facilitated influence appears to be mediated by differential levels of DHEA-sulfatase in lymphoid tissues. DHEA-sulfatase is an enzyme capable of converting DHEA-sulfate (inactive) to the active hormone DHEA. We find very high activities of this enzyme isolated in murine macrophages. The implications of our findings to immunobiology are very great, and indicate that T cells, while clonally restricted for antigen peptide recognition, also appear to exhibit an extreme flexibility with regards to the species of lymphokines they produce after activation. Regulation of this highly conservative mechanism appears to be partially, if not exclusively, controlled by cellular influences being exerted by distinct species of steroid hormones, supplied in an endocrine or a paracrine manner where they mediate either systemic or tissue-localized influences, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Presence of epidermal-derived thymocyte activating factor/interleukin 1 in normal human stratum corneum.

Keratinocytes produce a molecule, epidermal-derived thymocyte activating factor (ETAF), which is biologically and physiochemically similar to the polypeptide hormone interleukin 1 (IL-1). Because the stratum corneum (SC) is composed of terminally differentiated keratinocytes, we questioned whether ETAF/IL-1 could be isolated from this tissue. The extraction of normal human SC with a physiologic saline solution yielded a large amount of ETAF/IL-1 activity, as measured by the in vitro thymocyte co-stimulator assay. SC-derived ETAF/IL-1 (scETAF/IL-1) eluted from a sizing column with an approximate molecular weight of 15,000, and demonstrated three isoelectric point forms after separation on a chromatofocusing column. By these physiochemical characteristics, scETAF/IL-1 was found to be similar, if not identical to human keratinocyte- and macrophage-derived ETAF/IL-1. Further, a number of biologic effects known to occur in vivo after the administration of ETAF/IL-1, such as fever, neutrophilia, and an increase in plasma levels of acute-phase proteins, were all induced by the injection of scETAF/IL-1 into endotoxin-nonresponsive mice. scETAF/IL-1 was also found to stimulate collagenase production by human fibroblasts in vitro. In summary, our studies have established that normal human SC contains a large quantity of scETAF/IL-1. Whether scETAF/IL-1 integrates into the earliest afferents phases of local inflammatory responses, or merely represents a means of disposal of excessively produced hormone is currently unresolved.

Heparin effect on DNA synthesis in a murine fibrosarcoma cell line: influence of anionic density.

The effects of heparin subfractions on DNA synthesis in a murine cutaneous fibrosarcoma cell line were examined. Porcine mucosal heparin was preparatively fractionated for anionic charge density by DEAE-Sephadex chromatography and for molecular weight by Sephadex G-100 filtration. The cell line was plated from confluent monolayer cultures and grown in medium and fetal bovine serum, with or without a heparin fraction at a final concentration of 10 micrograms/ml. At intervals thereafter, the cells were pulsed with [3H]thymidine. A low-charge density heparin fraction stimulated [3H]thymidine incorporation (cpm/mg protein and cpm/cell) during the first 3 days of growth compared to control values without added heparin, whereas a high-charge density heparin fraction had little of this effect (186 +/- 35% of control vs. 101 +/- 14%, respectively; P less than .05). The augmentation of DNA synthesis observed with the low-charge density fraction correlated with increased proportions of cells in S and G2 phases compared with those of the controls, as determined by flow cytofluorometry. Low- and high-molecular-weight heparin fractions did not significantly alter DNA synthesis. Heparin subfractions are thus heterogeneous with respect to their effect on cellular DNA synthesis in this tumor line.

Clonal origin of tumors induced by ultraviolet radiation.

Skin tumors were induced in (C3H/HeN X C3H/HeN-PGK-1a)F1 female mice, heterozygous at the X-linked phosphoglycerate kinase-1 (PGK-1) locus, by exposure to the carcinogenic influence of ultraviolet radiation (UVR), 3-methylcholanthrene [(MCA) CAS: 56-49-5], or benz[a]pyrene [(BP) CAS: 50-32-8]. An assessment of the clonal origin of these tumors was accomplished through an analysis of the PGK-1 enzyme phenotype expressed by the transformed cells. In vitro culture was employed as a means of depleting nontransformed cells of host origin from the induced tumors. Cultured lines derived from tumors induced by each of the above agents were found to express only one of the two enzyme forms encoded by the host genotype, consistent with the probability that all the UVR-, MCA-, and BP-induced tumors examined in this study were monoclonal in origin. For further substantiation of the monoclonality of UVR-induced tumors, 2 UVR-induced tumors were enzymatically dissociated immediately following excision from the primary hosts, and the resulting cell suspensions were cloned in soft agar. Upon analysis, each set of clones selected in soft agar expressed only a single PGK-1 enzyme form. To rule out the possibility that the apparent monoclonality of culture-adapted tumor lines was due to in vitro selection, tumors that arose in UVR-treated PGK-1a/b female heterozygote mice were transplanted into PGK-1a and PGK-1b homozygous recipients. These transplanted tumors expressed a single PGK-1 allozyme following growth in recipients that were genetically homozygous for the major PGK-1 enzyme form expressed by the tumor prior to transplantation. These data strongly support the concept that most, if not all, UVR-induced tumors are derived from the progeny of a single transformed cell. This observation is important to the understanding of the nature of tumor-specific transplantation antigens expressed by individual UVR-induced tumors and indicates that such antigens also are clone specific. In addition, the results of this study indicate that polyclonality does not play a significant role in the generation of cellular and phenotypic heterogeneity known to be present within individual UVR-induced tumors.

Tumors arising from injection of cultured murine placental cells into normal animals: direct evidence for placental origin of tumors of two histologic types.

Long-term culture of placentas obtained from the mating of a congenic C3H male mouse carrying a unique electrophoretic variant of the X-chromosome-linked enzyme phosphoglycerate kinase (PGK-1) and a normal C3H female mouse has resulted in cell lines that have apparently undergone spontaneous malignant transformation in vitro. When injected into normal syngeneic animals, these cell lines have given rise to invasive carcinomas of two distinct histologic types, an adenocarcinoma and a poorly differentiated carcinoma. Both were demonstrated to be of placental origin by the continued presence of the allozyme coded on the paternal X-chromosome. Compared to murine tumors of other etiologies, these cell lines were characterized by a high intracellular alkaline phosphatase concentration.

Skin cancer development in mice exposed chronically to immunosuppressive agents.

Inbred female C3Hf/HeN, murine mammary tumor virus-negative mice exposed to either UV light or benzo[a]pyrene (BP), were subjected to four different chronic immunosuppressive regimens to determine their effect on skin cancer development. The immunosuppressive agents were cyclophosphamide, methotrexate, cortisone, and heterologous antilymphocyte globulin. Because of an unexpectedly high morbidity and mortality of mice exposed to chronic immunosuppressive measures, the dosages were kept at a level that permitted them to survive but did not prolong allogeneic skin graft survival and lower antibody titers, nor did this level diminish proliferative responses of lymphocytes to mitogens or allogeneic lymphocytes. Nevertheless, the latency periods (time interval between beginning of medication and appearance of skin tumors) of tumors in mice exposed to immunosuppressant measures were significantly shortened in several groups of mice exposed to UV and subjected to cyclophosphamide, cortisone, or antilymphocyte globulin and mice exposed to BP and subjected to cortisone acetate. In 3 groups, spindle cell tumors (fibrosarcomas) shifted to squamous cell carcinomas. A suppressed immune function would not be regarded as the mechanism for the observed responses because immunosuppression was not detected in the experimental mice.

Dietary restriction from middle age attenuates age-associated lymphoma development and interleukin 6 dysregulation in C57BL/6 mice.

Dietary restriction (DR) started in middle age profoundly reduces the occurrence of lymphoma in C57BL/6 mice. Here, we report immunocellular and molecular changes associated with this mode of cancer prevention. Twelve-month-old male C57BL/6 mice were either fed a control diet or subjected to moderate DR (approximately 25% < control intake). DR significantly reduced lymphoma development (incidence at 25 months, 19% of 72 control mice versus 5% of 60 DR mice). Flow cytometry of splenocytes showed that DR increased the percentage of CD4+ and CD8+ cells. Lymphomatous spleens displayed varied labeling patterns and high percentages of cells in S phase. Splenocyte c-myc expression tended to increase with age in controls and was reduced by DR. Lymphopenia and markedly reduced nucleated cell yields from peripheral lymphoid tissues were induced by DR. Serum interleukin 6 levels increased with age and were quite high (> 2500 pg/ml) in several mice with lymphoma and other histopathological findings. DR attenuated this age-associated increase. Immunohistochemical studies of lymphomatous spleens showed the presence of interleukin 6 in monocytic appearing cells but not in lymphoma cells. These observations support the possibility that an age-associated interleukin 6 dysregulation is important in lymphomagenesis.

Membrane-associated NAD+ glycohydrolase from rabbit erythrocytes is solubilized by phosphatidylinositol-specific phospholipase C.

NAD+ glycohydrolase (NADase) present on the surface of rabbit erythrocytes is a membrane-bound ectoenzyme that can be solubilized by phosphatidylinositol-specific phospholipase C (PIPLC). As much as 70% of the cell-associated NADase was made soluble by treatment with PIPLC. The portion of NADase that remained cell-associated after an initial PIPLC treatment proved to be resistant to subsequent solubilization attempts. Further analysis showed that release of NADase from erythrocytes could not be attributed to the action of proteinases or phospholipase C. Erythrocytes obtained from other mammals were analyzed and found to have variable amounts of PIPLC-susceptible NADase. Practically, this finding can be used to easily solubilize membrane-bound NADase as a first step in its purification.

Natural regulators of T-cell lymphokine production in vivo.

The mammalian immune system possesses the intrinsic capacity to evoke a wide variety of functionally distinct effector mechanisms following stimulation by a particular antigenic substance. Such diversity in available responses is absolutely essential to the immunocompetent host, which must continually deal with a diverse set of potential pathogens within its ever-changing environment. The development of appropriate types of immune responses, therefore, represents a highly dynamic process that requires that an equivalent consideration be given to a large array of components, any one of which is capable of modulating the final outcome. While the nature and complexity of the antigen(s), plus the intracellular or extracellular mode of presentation, provide specificity and some selection to the developing process, the route of antigen entry, as well as the physiological status of the host at the time of antigen insult, also contribute significantly to the formation of any immune response. The overall objective of this article is to introduce the concept that platelet-derived growth factor (PDGF) (either preformed or synthesized in response to stimulation), plus a number of steroid hormones (some of which are end-organ metabolized at local tissue sites), can all play significant roles in the genesis of immunologic responses in vivo.

Tumor-susceptibility generated in mice treated with subcarcinogenic doses of 8-methoxypsoralen and long-wave ultraviolet light.

Evidence is presented to show that mice treated with various regimens of 8-methoxypsoralen followed by exposure to long-wave ultraviolet light (PUVA) are rendered tumor-susceptible when challenged with short-wave ultraviolet light (UVB) induced regressor tumors. These same tumors are readily rejected when implanted into normal syngeneic animals. Similar observations have been made in mice treated with subcarcinogenic doses of UVB, where it was shown that the tumor-susceptible state is mediated by suppressor T lymphocytes. These suppressor T-cells may be generated in response to antigens expressed by UVB damaged skin cells. It is now known that suppressor T-cells generated in mice treated with UVB are Ia-positive and have specificities for cross-reacting tumor antigens shared by all UVB-induced tumors, which have been tested to date. Our data suggest that, like UVB treated mice, treatment of mice with PUVA results in tumor-susceptibility mediated through the generation of Ia+ suppressor cells. Since PUVA treatments appear to generate a suppressor cell response in mice, a possible mechanism by which these treatments act to manage autoimmune type skin diseases, such as vitiligo, is discussed.

The effects of high-dose UV exposure on murine Langerhans cell function at exposed and unexposed sites as assessed using in vivo and in vitro assays.

Exposure of mice to a single large dose of UV radiation leads to a systemic inability of these mice to develop effective contact hypersensitivity (CS) responses to epicutaneously applied dinitrofluorobenzene (DNFB). Although this effect requires time to develop when unirradiated skin sites are used for CS sensitization, it is observed immediately at the site of UV exposure. Unirradiated skin sites on mice exposed to a single large dose of UV radiation 3 days previously were found to contain histochemically detectable ATPase+ cells with normal morphology and in normal densities, and yet CS responses were not induced to DNFB applied to these sites. Epidermal cells (EC) obtained from these skin sites were found to be capable of providing accessory cell (AC) function in in vitro T-cell proliferation assays that was qualitatively similar to EC obtained from unirradiated mice, thus indicating that exposure of mice to a single large dose of UV radiation does not induce a systemic AC dysfunction. Indeed, increased levels of AC activity were obtained in EC prepared from the UV-irradiated skin sites on the third day following UV exposure. This latter effect may be due to an influx of inflammatory cells into the irradiated site in response to the tissue damage caused by the UV radiation. We hypothesize that the inflammatory response induced by the cytodestructive effects of the UV treatment may play a central role in the generation of the systemic suppression of induction of CS responses, perhaps through the induction of acute-phase proteins.

Parallel recovery of epidermal antigen-presenting cell activity and contact hypersensitivity responses in mice exposed to ultraviolet irradiation: the role of a prostaglandin-dependent mechanism.

Contact hypersensitivity (CH) responsiveness to 2-4-dinitro-1-fluorobenzene (DNFB) is depressed in mice that are sensitized through skin sites exposed to ultraviolet radiation (UVR). This is partially due to a reduction in antigen-presenting cell (APC) activity within UVR-exposed skin, a condition marked by a decrease in the density of ATPase/Ia-positive epidermal cells. The purpose of this study was to correlate the histological and functional recovery of APC activity in the skin of C3H mice exposed to low-dose (4 X 450 J/m2) or high-dose (1 X 15 kJ/m2) UVR with the normalization of CH responsiveness. Skin biopsy specimens taken at various intervals after UVR exposure revealed a rapid recovery in the density of ATPase/Ia positive cells: about 70% of normal by 3 days, and normal after 5 days. Functional analyses showed that lymph node cells obtained from donors that were sensitized with DNFB 3 days after UVR treatment transferred normal ear-swelling responsiveness to non-primed recipients, thus indicating that APC activity in UVR-exposed skin paralleled the recovery of ATPase/Ia-positive epidermal cells. This suggested that an alternative mechanism causes the persistent depression of CH in mice exposed to UVR. Mice pretreated with indomethacin prior to UVR exposure demonstrated a capacity to elicit CH responses to DNFB, which paralleled the histological and functional recovery of APC in the skin (i.e., normal CH responses were elicited 3 days after exposure to UVR). We conclude from this study that APC activity in the skin recovers rapidly after exposure to UVR, and that a PG-dependent mechanism is responsible for many of the persistent and systemic effects that cause a depression in the CH responsiveness of mice treated with UVR.

Experimental photoimmunology: immunologic ramifications of UV-induced carcinogenesis.

The use of animal model systems to investigate the sequence of events which lead to the induction and progression of skin tumors following chronic ultraviolet light (UVL) exposure has clearly shown that the direct mutagenic effects of UVL is only one of the components involved in this process. In spite of the fact that overt carcinogenesis is only one of the many effects produced by UV light, most hypotheses as to the mechanism by which UVL can cause the mutations necessary to achieve the transformed phenotype have focused on the direct effects of UVL on DNA and the generation of carcinogenic compounds. Investigations during the last 5 yr, however, have clearly demonstrated that immunologic factors are also critically important in the pathogenesis of UV-induced skin cancers. A complete understanding of UV-carcinogenesis must therefore consider the mechanisms which allow the transformed cell to evade immunologic rejection by the host in addition to those aspects which deal with conversion of a normal cell to a cancer cell. It is the object of this review to provide both a historical account of the work which established the immunologic consequences of chronic UVL exposure and the results of recent experiments designed to investigate the kinetics and mechanisms by which UVL affects the immunologic apparatus. In addition, a hypothetical model is presented to explain the sequence of events which ultimately lead to the emergence of the suppressor T-cells which regulate antitumor immune responses.

The effect of various sunscreen agents on skin damage and the induction of tumor susceptibility in mice subjected to ultraviolet irradiation.

Sunscreen preparations containing various chemical UV absorbers, para-aminobenzoic acid (PABA), 2 PABA derivatives, benzophenone or a combination of these were topically applied to the backs of C3H/HeN mice prior to their being irradiated with ultraviolet light in the UVB range. In all cases this treatment was effective in preventing the pathological skin changes associated with UVB irradiation. Histological evaluation of skin biopsies from mice treated with the sunscreen preparations and UVB irradiation showed little or no difference from normals in amount of hyperplasia, melanization or parakeratosis present. These histologic changes were observed in animals receiving UVB irradation in the absence of any sunscreen agent. Pretreatment with the various sunscreen agents did not, however, prevent the induction of tumor susceptibility as measured by the sustained growth of a UV-induced tumor which is immunologically rejected in normal syngeneic mice. These data show a clear distinction between the effects of UVB irradiation leading to histological changes in the epidermis and those leading to the state of tumor susceptibility in mice. The distinction was further corroborated by the finding that epidermal hyperplasia induced by repeated applications of croton oil had no significant enhancing or inducing effects on the induction of tumor susceptibility. In addition, the induction of tumor susceptibility. In addition, the induction of tumor susceptiblity is not due to wavelengths of light less than 320 nm since this effect was abrogated when the UVB radiation was filtered through glass. Possible mechanistic differences between the tumor susceptiblity generated in UVB and photoprotected UVB irradiated animals were observed, however, when we attempted to adoptively transfer the state of tumor susceptibility to normal animals. While it was readily transferable with splenic lymphoid cells from UVB irradiated animals, all attempts to transfer the tumor susceptibility from photoprotected animals have, to date, been unsuccessful.

Regulation by the skin of lymphoid cell recirculation and localization properties.

The existence of epidermal Langerhans cells, Ia-positive dermal dendritic cells, lymphocytes which can demonstrate epidermitropism, and keratinocytes capable of secreting Interleukin-1-like molecules, each support the concept that skin can function as an immunologic organ. Such conclusions are further strengthened by the knowledge that both afferent and efferent immune responses can take place exclusively within the skin. The purpose of our study was to evaluate the ability of skin to regulate lymphoid cell recirculation and localization properties. The use of ultraviolet radiation as an exogenous stimulus resulted in a pronounced redistribution of antigen-presenting cells from central (spleen) to peripheral (skin and lymph node) lymphoid tissues as well as marked increase in the rate of lymphocyte entry into skin draining lymph nodes. This latter condition was due to elevations in the quantitative levels of high endothelial venules present within the peripheral lymph nodes. The ability of epidermal keratinocytes to express Class II molecules is known to be associated with a number of skin diseases. However, the functional significance of this phenomenon is unknown. The results of our studies, employing a nude mouse model, indicate that the expression of Class II molecules by keratinocytes facilitates the movement of Langerhans cell precursors into the epidermis and may also function to enhance lymphocyte entry into the skin. We conclude that nonlymphoid components resident within the skin can influence essential aspects of the adaptive immune response through the production of soluble factors (e.g., Interleukin-1 or through the cellular expression of Class II molecules.

Steroids as regulators of the mammalian immune response.

The mammalian immune system is multicellular in composition, and its proper function requires careful control over complex developmental pathways and many distinct types of effector responses. Numerous overlapping mechanisms of intercellular communication are needed to accomplish the tasks of proper regulation of the diverse cell types that constitute this essential protective system. One mechanism occurs by direct cell-to-cell contact through the interaction of membrane-associated molecules. Examples of this type of communication include the interaction that takes place between the antigen-specific T-cell receptor and the foreign peptides that are bound to major histocompatibility complex molecules, as well as costimulatory molecule interactions with their specific ligands expressed on antigen-presenting cells (e.g., CD28 and B7-1 or B7-2). A second mechanism occurs through the production, secretion, and activities of soluble mediators, collectively known as the cytokines. The cytokines are represented by a large and diverse group of molecules that are produced by a wide variety of cell types. Unique species of cytokines bind to specific membrane-associated receptors on target cells, inducing the activation of particular signal-transduction pathways. These processes subsequently lead to the diversity of cytokine-linked changes in cellular physiology. Some of the cytokines exert their influences in vivo via endocrine routes, although it is far more common for intercellular communication via cytokines to occur microenvironmentally via paracrine or autocrine pathways. The object of this review is to provide evidence supporting the concept that one mechanism for upstream regulation of cytokine production by immunocompetent cell types is controlled by the regulatory activities of various steroid hormones. Strain variation in susceptibility to infectious agents, the condition of immunosenescence, and the processes that control the development of common mucosal immunity are used as examples of immune mechanisms that may be under steroid hormone control.

Regulation of macrophage dehydroepiandrosterone sulfate metabolism by inflammatory cytokines.

Metabolism of dehydroepiandrosterone sulfate (DHEAS) to dehydroepiandrosterone (DHEA) occurs within specific anatomical compartments in vivo through the actions of the enzyme DHEAS sulfatase. This enzymatic activity facilitates the conversion of hydrophilic DHEAS to the hydrophobic species DHEA, which can then be further metabolized to other steroid hormones. High levels of DHEAS sulfatase reside in tissues where the biological activity of DHEA or its downstream metabolites regulate cellular function. Therefore, control over the activity of DHEAS sulfatase may represent an important regulatory process for the production of DHEA and its metabolites. Homogeneous populations of macrophages from normal mice were found to effectively convert DHEAS to DHEA in vitro. DHEAS sulfatase activity could be markedly depressed after exposure of these cells to a variety of nonspecific macrophage activators [i.e. zymosan, polyinosine/cytosine, heat-killed bacteria, or bacterial lipopolysaccharide (LPS)]. Inhibition of DHEAS metabolism was found to require protein synthesis, because temporary abrogation of protein synthesis with cycloheximide eliminated the ability of LPS to depress the conversion of DHEAS to DHEA. Additionally, exposure of LPS-nonresponsive macrophages to supernatants derived from LPS-treated BALB/c macrophages inhibited their ability to convert DHEAS to DHEA. Potent inhibition of sulfatase activity could be achieved by directly exposing murine macrophages to interferon-alpha (IFN alpha), IFN beta, or tumor necrosis factor-alpha, but not interleukin-1, interleukin-6, granulocyte-macrophage colony-stimulating factor, transforming growth factor-beta, platelet-derived growth factor, or the T-cell product IFN gamma. Our results indicate that macrophage metabolism of DHEAS to DHEA is down-regulated after cellular activation. Furthermore, inhibition of DHEAS sulfatase activity appears to be mediated through the actions of the inflammatory cytokines tumor necrosis factor-alpha and IFN alpha/beta.

Modification of immunological potential by ultraviolet radiation. II. Generation of suppressor cells in short-term UV-irradiated mice.

When normal mice are exposed for short periods to ultraviolet light (UV), they support the progressive growth of transplanted syngeneic UV-induced tumors. Normal nonirradiated mice almost always reject these tumor implants. The UV-mediated suppression of the antitumor response can be adoptively transferred to normal syngeneic mice with lymphoid cells derived from short-term UV-irradiated donors. Transfer of the suppressive effect is dosage dependent and also appears to require the presence of viable T lymphocytes. Suppressive activity was observed in both the spleen and thymus of UV-irradiated donors. In the preceding paper we have established that UV irradiation does not cause a general depression of testable immune functions. Collectively these data suggest that short-term UV irradiation of mice leads to an increase in suppressor cell activity, thereby causing an inhibition in the host's ability to respond to an antigenic UV-induced tumor. The possible role of this phenomenon in the mechanism of UV carcinogenesis is discussed.