Role of antigen-presenting cells in the development and persistence of contact hypersensitivity

Cyclophosphamide-modified murine peritoneal macrophages induce CD4+ T contrasuppressor cells that protect contact sensitivity T effector cells from suppression

BACKGROUND

Cyclophosphamide (CY) is one of the most widely used alkylating agents in the treatment of various cancers and some autoimmune diseases. Numerous reports suggest that CY exerts immunoregulatory effects. Animal studies have shown CY affects contact sensitivity (CS) response by depleting CD4⁺CD25⁺ T regulatory cells and CD8⁺ T suppressor (Ts) cells. In a mouse model of CS, we previously showed that in vivo treatment with CY shapes the immunogenic/immunoregulatory balance of peritoneal macrophages. The aim of the current study is to verify if macrophages (Mf) from CY-treated mice are indeed able to induce immunoregulatory cells that could protect from suppression.

METHODS

Adoptive cell transfer of CS was used to examine immunomodulating properties of peritoneal Mf from CY-treated mice. Isolation of peritoneal Mf from animals that were (Mf-CY) or were not (Mf) treated with CY were cultured to identify cytokine repertoire. Further, we assessed spleen cell (SPLC) cytokine production following immunization with trinitrophenyl-conjugated Mf from donors treated (TNP-Mf-CY) or non-treated (TNP-Mf) with CY.

RESULTS

In vitro experiments identified that Mf-CY produce more IL-6, TNF-α and TGF-β than naïve Mf. Further, immunization with peritoneal TNP-Mf-CY induces CD4⁺ T contrasuppressor cells (Tcs) cells that protect CS-effector cells from suppression. Higher IL-17A secretion was observed from TNP-Mf-CY-treated mouse SPLC compared to SPLC from TNP-Mf injected mice suggesting that this cytokine might be important in mediating contrasuppression in this model.

CONCLUSIONS

Our results show that in vivo treatment with CY influences mouse peritoneal Mf to induce CD4+ Tcs cells that protect CS-effector cells from suppressive signals of Ts cells.

Some new perspectives on transplantation immunity and tolerance

To provoke a rejection response, an allograft's antigens must be presented to the host by accessory cells of the graft's MHC genotype. Tolerance induction, too, in neonatal rodents is an MHC-restricted response: third party grafts on tolerant animals survive longer if they are MHC-compatible with the tolerizing cells, rather than the host. In this article, Willys Silvers and his colleagues review the evidence for these observations and discuss their implications.

Effector and regulatory mechanisms in allergic contact dermatitis

Allergic contact dermatitis (ACD), one of the commonest occupational diseases, is a T-cell-mediated skin inflammation caused by repeated skin exposure to contact allergens, i.e. nonprotein chemicals called haptens. Allergic contact dermatitis, also referred to as contact hypersensitivity, is mediated by CD8+ T cells, which are primed in lymphoid organs during the sensitization phase and are recruited in the skin upon re-exposure to the hapten. Subsets of CD4+ T cells endowed with suppressive activity are responsible for both the down-regulation of eczema in allergic patients and the prevention of priming to haptens in nonallergic individuals. Therefore, ACD should be considered as a breakdown of the skin immune tolerance to haptens. Recent advances in the pathophysiology of ACD have demonstrated the important role of skin innate immunity in the sensitization process and have revisited the dogma that Langerhans cells are mandatory for CD8+ T-cell priming. They have also introduced mast cells as a pivotal actor in the magnitude of the inflammatory reaction. Finally, the most recent studies address the nature, the mode and the site of action of the regulatory T cells that control the skin inflammation with the aim of developing new strategies of tolerance induction in allergic patients.

Antigen-presenting cells, including Langerhans cells, veiled cells and interdigitating cells

The accessory functions attributed to macrophages, such as antigen presentation, are probably carried out by specialized, marrow-derived cells which always have Ia antigen on their surfaces. These cells are not actively phagocytic, but are mainly engaged in engulfing large volumes on fluid. They are found in the epidermis as sessile cells, the Langerhans cells, but some re-enter the dermis and appear in afferent lymph as actively moving, veiled cells. Here they are joined by other veiled cells which have differentiated in the dermis: both populations then enter the draining lymph node. A similar process of differentiation probably occurs in other specialized tissues leading to the formation of cells that enter the afferent lymph and become veiled cells. In the lymph node, veiled cells localize in the paracortex or T-dependent area and later differentiate into another sessile cell type, the interdigitating cell. The life-style of this family of cells appears to be well-adapted for the transport of antigen into the paracortex, an area from which free antigen is largely excluded, and it seems likely that T-cell activation is triggered by the arrival of veiled cells bearing a new antigen on their surfaces.

A cross-reactive tick cement antigen is a candidate broad-spectrum tick vaccine

Truncated constructs of 64P (64TRPs), a secreted cement protein from salivary glands of the tick Rhipicephalus appendiculatus, provided cross-protection against Rhipicephalus sanguineus and Ixodes ricinus, apparently by targeting antigens in the midgut and salivary glands of adults and nymphs, causing mortality. Tick feeding on 64TRP-immunised animals stimulated local inflammatory immune responses (involving basophils, eosinophils, lymphocytes, mast cells, macrophages and dendritic-like cells) that boosted the immune status of vaccinated animals. The vaccine trial results, and antigenic cross-reactivity of 64TRPs with R. sanguineus, I. ricinus, Amblyomma variegatum and Boophilus microplus, indicate the potential of 64TRPs as a broad-spectrum anti-tick vaccine.

Thalidomide Inhibits Tumor Necrosis Factor-α Production and Antigen Presentation by Langerhans Cells

Thalidomide is an effective treatment for several inflammatory and autoimmune disorders including erythema nodosum leprosum, Behcet's syndrome, discoid lupus erythematosus, and Crohn's disease. Thalidomide is believed to exert its anti-inflammatory effects, at least in part, by inhibiting tumor necrosis factor-alpha (TNF-alpha) production by monocytes. We studied the effects of thalidomide on epidermal Langerhans cells (LC). LCs are epidermal antigen-presenting dendritic cells that play important roles in skin immune responses. Using the murine epidermis-derived dendritic cell lines, XS106A from A/J mice and XS52 from BALB/c mice as surrogates for LC, we found that thalidomide inhibited TNF-alpha production in a concentration-dependent manner. Northern blot analysis revealed that thalidomide significantly decreased the peak-induced mRNA level of TNF-alpha in XS106A cells and XS52 cells. We then examined the effect of thalidomide on fresh LC enriched to approximately 98% using positive selection of Ia+ cells with antibodies conjugated to magnetic microspheres. TNF-alpha production was reduced by 67.7% at a thalidomide concentration of 200 microg per mL. Thalidomide also had a profound inhibitory effect on the ability of LC to present antigen to a responsive TH1 clone. Thalidomide inhibits TNF-alpha production and the antigen-presenting ability of epidermal LCs. These mechanisms may contribute to the therapeutic effects observed with this agent.

The beneficial effect of donor-specific transfusions: a review of existing explanations and a new hypothesis based on a relatively unapplied theory of T cell immunoregulation. A regulatory hypothesis in progress

The mechanism by which donor specific transfusions protect a graft from the recipient's immune system is unknown. It is likely that this beneficial mechanism is a subset or distinct exhibition of the general rules governing the regulation of the immune system. This phenomenon provides a strong framework for investigation of immune regulation, considering its potential consanguinity to immune regulation, that it is a paradox representing a manifestation of regulatory rules, and that it provides a wealth of clinical experience and experimentation from which to make inferences. Vital in any exploration of immune regulation, is the promise held in reducing the immune system to its chief elemental regulatory mechanisms and interactions. Strangely, the majority of this consequential work may have already been accomplished by Gershon, Green and colleagues with their elegant demarcation of T cell regulation into suppressor and contrasuppressor pathways. The practical and theoretical implications of this discovery seem to be, for the most part, ignored by mainstream immunology. It is doubtful, based on the quality and quantity of their work, or confirming work by other laboratories that they were inaccurate in their findings. It remains a horrible waste that their discoveries are not in immunology's pantheon of hallowed discoveries and are little used. With all this kept in mind, a comprehensive hypothesis of regulation was put together based mainly on Gershon's portrait of the suppressor and contrasuppressor pathways' contributions to immune regulation and experimentation surrounding the unsolved paradox of donor specific transfusions.

Human T lymphocyte priming in vitro by haptenated autologous dendritic cells

Dendritic cells (DC), generated from adherent peripheral blood mononuclear cells (PBMC) by culturing with granulocyte-macrophage colony-stimulating factor (GM-CSF) and IL-4, were used to study in vitro sensitization of naive, hapten-specific T cells and to analyse cross-reactivities to related compounds. DC were hapten-derivatized with nickel sulphate (Ni) or 2-hydroxyethyl-methacrylate (HEMA), followed by tumour necrosis factor-alpha (TNF-alpha)-induced maturation, before autologous T cells and a cytokine cocktail of IL-1beta, IL-2 and IL-7 were added. After T cell priming for 7 days, wells were split and challenged for another 7 days with Ni or HEMA, and potentially cross-reactive haptens. Hapten-specificity of in vitro priming was demonstrated by proliferative responses to the haptens used for priming but not to the unrelated haptens. Highest priming efficiencies were obtained when both IL-4 and IL-12 were added to the cytokine supplement. Marked interferon-gamma (IFN-gamma) release (up to 4 ng/ml) was found when IL-12 was included in the cultures, whereas IL-5 release (up to 500 pg/ml) was observed after addition of IL-4 alone, or in combination with IL-12. Nickel-primed T cells showed frequent cross-reactivities with other metals closely positioned in the periodic table, i.e. palladium and copper, whereas HEMA-primed T cells showed distinct cross-reactivities with selected methacrylate congeners. Similar cross-reactivities are known to occur in allergic patients. Thus, in vitro T cell priming provides a promising tool for studying factors regulating cytokine synthesis, and cross-reactivity patterns of hapten-specific T cells.

Antigen-presenting cell function of epidermal cells activated by hapten application

Exposure to haptens initiates a series of immune and inflammatory reactions that cause migration of epidermal Langerhans cells (LC) to draining lymph nodes, antigen processing, and presentation to T cells. In the present study, the antigen-presenting cell (APC) function of epidermal cells (EC) following hapten application was determined using a cell transfer system. This function of EC in inducing contact sensitivity (CS) in the recipient mice appeared as early as 6 h after hapten painting, and reached its maximum at 24 h. The amount of hapten on EC did not correlate with the function, i.e. the amount retained on the cells was greatest immediately after hapten painting and decreased over time. Several experiments were performed to identify the cell type responsible for the APC function. Through immunomagnetic bead separation, the APC function was detected in Ia- EC, as well as in unfractionated EC from hapten-painted mice. A purified population of Ia+ cells (LC) induced CS with much less efficiency than unseparated cells. Depletion of LC by anti-Ia monoclonal antibody (mAb) and complement-mediated lysis did not impair the APC function, whereas it was reduced by the depletion of Thy-1+ cells by anti-Thy-1 mAb and complement-mediated lysis. Moreover, adherent cells that were harvested from a 48-h culture of EC obtained from hapten-painted skin, and were free of contaminating LC and gamma omega T cells, had a strong capacity to induce CS. These findings indicate that keratinocytes (KC) acquire APC function as well as LC, with hapten application. Phenotypically increased expression of intercellular adhesion molecule-1 (ICAM-1) and Thy-1 on EC was observed following hapten application, whereas expression of Ia and B7/BB1 was unaltered. The APC function of EC from hapten-painted skin was dependent on ICAM-1 and Thy-1 expression, as the mAbs for these molecules reduced the capacity to induce CS. These results suggest that hapten application induces not only LC but also KC to mature functionally and become potent APCs, and that these KC exert the APC function complementarily at local sites following the migration of LC with potent APC function to the draining lymph node.

Dual Role of Dendritic Cells in the Induction and Down-Regulation of Antigen-Specific Cutaneous Inflammation

We have previously reported that contact sensitivity (CS) to dinitrofluorobenzene (DNFB) in C57BL/6 mice was mediated by MHC class I-restricted CD8+ T cells and down-regulated by MHC class II-restricted CD4+ T cells. In this study, we analyzed the contribution of dendritic cells (DC) in the induction of these two T cell subsets endowed with opposite functions. Hapten-pulsed skin- and bone marrow-derived DC, obtained from either normal C57BL/6 mice or from MHC class II (I+II−) and MHC class I (I−II+)-deficient mice, were tested for their ability to prime normal mice for CS to dinitrofluorobenzene. Expression of MHC class I molecules by transferred DC was mandatory both for the induction of CS and for the generation of hapten-specific CD8+ T cells in lymphoid organs. I+II− DC were as potent as I+II+ DC in priming for CS, demonstrating that activation of effector CD8+ T cells can occur independently of CD4+ T cell help. I−II+ DC could not immunize for CS, although they could sensitize for a delayed-type hypersensitivity reaction to protein Ags. Moreover, I−II+ DC injected simultaneously with cutaneous sensitization down-regulated the inflammatory response, suggesting that hapten presentation by MHC class II molecules could prime regulatory CD4+ T cells. These results indicate that DC can present haptenated peptides by both MHC class I and class II molecules and activate Ag-specific CD8+ effector and CD4+ regulatory T cell subsets, concurrently and independently.

MHC class I+/II- dendritic cells induce hapten-specific immune responses in vitro and in vivo

Activation requirements and biologic properties of hapten-specific, major histocompatibility complex class I-restricted CD8+ T lymphocytes are not fully understood. To address this issue, a novel CD45+/major histocompatibility complex class I+ (H-2k)/II-/CD80+ dendritic cell line, termed 80/1, which is capable of stimulating naïve, allogeneic CD8+ but not CD4+ T cells in vitro, was derivatized with trinitrobenzenesulfonic acid and co-cultured for 4 d with syngeneic, naïve CD8+ T cells. Results obtained showed that trinitrophenyl-derivatized, but not underivatized 80/1 dendritic cells, can induce vigorous proliferation ofCD8+ T cells. T-cell blasts generated in this fashion were able to lyse syngeneic, trinitrophenyl-derivatized targets but failed to lyse underivatized or trinitrophenyl-derivatized syngeneic, major histocompatibility complex class I- mutant cells or allogeneic targets. The ability of 80/1 dendritic cells to prime naïve, syngeneic T cells in vivo was tested in a contact hypersensitivity model. C3H/HeN mice were injected subcutaneously with identical numbers of (i) trinitrophenyl-derivatized 80/1 dendritic cells; (ii) trinitrophenyl-derivatized 80/1 dendritic cells fragmented by freeze-thawing cycles; (iii) trinitrophenyl-derivatized fibrosarcoma L929; and (iv) trinitrophenyl-derivatized lymphoma R1.1 cells. Whereas live trinitrophenyl-derivatized 80/1 dendritic cells were able to sensitize for contact hypersensitivity, killed hapten-derivatized 80/1 dendritic cells or control cells failed to do so. Thus, we conclude that 80/1 dendritic cells, when compared with major histocompatibility complex class I+ non-dendritic cells, can effectively prime naïve, syngeneic CD8+ T cells for hapten-specific responses, probably due to their better costimulatory and migratory properties.

Induction of low zone tolerance to contact allergens in mice does not require functional Langerhans cells

Epidermal Langerhans cells are known to be the major controlling element in the development of contact hypersensitivity. Haptenic molecules permeating the skin are taken up locally by Langerhans cells and then presented to T lymphocytes in the regional lymph nodes. Despite the presence of functional Langerhans cells, however, subsensitizing doses of hapten applied epicutaneously induce tolerance. We examined epidermal Langerhans cells at the site of contact with picryl chloride or oxazolone in BALB/c and C57B1/6 mice with regard to their responding to either subsensitizing or sensitizing doses of allergen. Subsensitizing doses did not interfere with the membranous adenosine triphosphatase system on Langerhans cells, known to relate to functional readiness of the cell. Accordingly, on electron microscopy the ultrastructure of Langerhans cells was found to be like that in untreated skin. In contrast, sensitizing doses caused a significant depletion of adenosine triphosphatase-positive Langerhans cells, and electron microscopy revealed marked cellular activation of Langerhans cells, with enlarged nuclei and increased numbers of mitochondria and Birbeck granules. Furthermore, subsensitizing doses induced tolerance regardless of whether Langerhans cells were functionally intact or had their function blocked arbitrarily. Blocking was achieved either by preceding ultraviolet B irradiation at the site of application or by painting of a sensitizer before painting another sensitizer on the same site. Moreover, not even surgical removal of the site within minutes after painting could prevent the induction of tolerance. The data suggest that subsensitizing doses of contact allergens painted on normal murine skin bypass involvement of epidermal Langerhans cells.

In situ changes in the relative abundance of human epidermal cytokine messenger RNA levels following exposure to the poison ivy/oak contact allergen urushiol

Abstract: Epidermal keratinocytes in culture have been shown to produce many cytokines, and their proteins have been identified in skin tissue samples. It has therefore been assumed that these cytokines are transcribed in vivo by the epidermis in response to contact allergens. In this report, in situ hybridization was used to detect the messenger RNAs for interleukin-1 alpha (IL-1 alpha), interleukin-1 beta (IL-1 beta) and tumour necrosis factor-alpha (TNF-alpha) in samples of human skin prior to and at various times after application of urushiol, the immunogenic component of poison ivy/oak. In sensitive subjects, IL-1 alpha and TNF-alpha mRNAs showed a progressive increase in transcript levels that paralleled the clinical and histological features of the inflammatory process. The time-course of the IL-1 beta response differed from that of IL-1 alpha and TNF-alpha, in that there was an early (by 6 h after urushiol administration) elevation in IL-1 beta mRNA that occurred before there was evidence of inflammation and had returned to background levels by 72 h when the reaction had reached its peak. In contrast to urushiol-sensitive subjects, urushiol-anergic individuals did not exhibit an increase in IL-1 alpha, IL-1 beta or TNF-alpha mRNA levels. The data provide evidence for an in vivo role for epidermal IL-1 alpha, IL-1 beta and TNF-alpha transcription in the regulation of IL-1 beta and TNF-alpha polypeptide levels in the epidermis in response to this common contact allergen.

Modulation of Ia+ Langerhans cell numbers in vivo by cultured epidermis derived supernatants and by GM-CSF

This paper demonstrates that epidermal cells in culture produce an activity which can increase the frequency of Ia+ epidermal Langerhans cells (LC). This was achieved by treating mice topically with a mixture containing supernatant derived from primary culture of murine epidermis (ES) and a synthetic corticosteroid, triamcinolone acetonide (TAC). The presence of the supernatant in the mixture partially protected the Ia+ LC from depletion by the steroid. The Ia+ LC frequency increasing activity was measured as the difference between the Ia+ LC frequency due to treatment with steroid mixed with supernatant and the Ia+ LC frequency due to treatment with steroid mixed with negative control medium. The mean frequency of Ia+ LC in epidermis treated with TAC mixed with ES was 606(SD 43) cells/mm2, as compared with 486 (SD 68) cells/mm2 in the epidermis treated with TAC mixed with control medium. The activity appeared to be caused by (a) proteinaceous factor(s). A fraction of ES which was retained above a > or = 10 KDa molecular weight cut-off membrane was capable of partially protecting Ia+ LC frequency from TAC depletion. Supernatants from cultured lymph nodes, dermis as well as the squamous cell carcinoma lines T7 and T79, but not the human osteosarcoma cell-line 143B, also contained similar activities. We demonstrate that GM-CSF also increased the number of Ia+ epidermal LC when applied topically to mouse skin in this system. Therefore, using this Ia+ LC frequency modulation system, we propose that GM-CSF is one example of a cytokine which may be involved in the regulation of Ia+ LC numbers in epidermis and that epidermal cells produce factors which can increase the number of Ia+ LC.

Regulation of transgenic class II major histocompatibility genes in murine Langerhans cells

I-E is a class II major histocompatibility complex molecule normally expressed by Langerhans cells. A series of transgenic mice were developed previously that carry E alpha d gene constructs with promoter-region deletions that cause expression of I-E by different cell types when maintained on a B6 (I-E[-]) genetic background. To study cis-acting gene sequences that regulate expression of class II proteins by Langerhans cells, we identified transgenic I-E expression by tissue immunoperoxidase staining and by epidermal cell suspension immunofluorescence cytometry. Mice with a transgene containing 1.4 kilobase pairs (kb) of flanking sequence 5' to the E alpha initiation site expressed barely detectable levels of I-E on a tiny percentage of Langerhans cells, indicating that sequences promoting Langerhans cell expression of E alpha exist between 2.0 and 1.4 kb 5' of the E alpha initiation site. Removal of an additional 170 bp of 5' flanking sequence caused near-normal levels of expression by approximately one third of epidermal Langerhans cells, which contrasts with studies that showed minimal transgene expression by splenic dendritic cells in these animals. Thus, sequences between 1.4 and 1.23 kb 5' of the E alpha initiation site decrease expression of I-E by epidermal Langerhans cells, but enable I-E expression by splenic dendritic cells. These studies identify Langerhans cell-specific regulatory sequences and genetic regions controlling major histocompatibility complex class II gene expression in Langerhans cells and splenic dendritic cells. The genetic regions identified may be particularly important because differential regulation of class II major histocompatibility complex protein synthesis by Langerhans cells and dendritic cells may be crucial to immune functions of intact animals.

Cyclophosphamide uncovers two separate macrophage subpopulations with opposite immunogenic potential and different patterns of monokine production

As shown previously, thioglycollate-induced peritoneal macrophages consist of two subpopulations which differ morphologically and functionally. When tagged with trinitrophenyl hapten (TNP), one macrophage subpopulation induced in vivo effector cells (Th1) of contact sensitivity (CS) reaction, while the other induced suppressor T cells (Ts) which inhibit CS and are highly sensitive to the in vivo action of cyclophosphamide (CY). Our present experiments show that CY-resistant (Th inducers) and CY-sensitive macrophages (Ts inducers) differ also in the spectrum of biologically relevant molecules which they secrete when stimulated by LPS. Thus macrophages which preferentially induce Th1 cells have a cytokine pattern IL-1LOW, IL-6HIGH, TNF-alpha LOW, while macrophages which recruit Ts cells are IL-1HIGH, IL-6LOW, TNF-alpha HIGH. TH1 inducers produced also somewhat better PGE2 then Ts inducers. Production of reactive nitrogen intermediates (NO/NO2-) was similar in both groups of macrophages. The reasons for the differential effect of CY on these two populations is not clear at present, although it is known that CY metabolites can bind to sulfhydryl groups on antigen presenting cells (APC) and thereby up- or downregulate the antigen presenting capacities of separate subpopulations of APC.

Interleukin-10 inhibits the primary allogeneic T cell response to human epidermal Langerhans cells

In this study, we analyzed the effect of interleukin-10 (IL-10) on the primary allogeneic T cell response induced by human Langerhans cells (LC), the dendritic cells from epidermis. We showed that IL-10 strongly inhibited the T cell response, provided it was added at the beginning of the mixed epidermal cell lymphocyte reaction (MELR). Proliferation of both CD4+ and CD8+ T cell subsets was affected by the cytokine. An inhibitory effect of IL-10 on human LC allostimulatory function was evidenced by the fact that IL-10-preincubated LC, but not IL-10-preincubated T cells, can display inhibitory effect. LC treatment with IL-10 partially inhibited the increase of HLA-DR expression on cultured LC as the percentage of highly positive HLA-DR cells was lower than that observed in the absence of the cytokine. IL-10 inhibited T cell alloreaction induced by 2-day-cultured human LC which constitutively display high levels of HLA class II, as well as ICAM-1 and LFA-3 antigens. This suggests that the suppressive effect of the cytokine was not merely related to an impaired up-regulation of these molecules. Addition of IL-1 during the MELR potentiated the allogeneic T cell proliferation and could reverse, at least partly, the inhibitory effect of IL-10. Collectively, these data indicate that IL-10 can prevent the alloreaction induced by human dendritic cells, providing new insights into the potential clinical use of this cytokine.

The skin as an immune organ

As a protective interface between internal organs and the environment, the skin encounters a host of toxins, pathogenic organisms, and physical stresses. To combat these attacks on the cutaneous microenvironment, the skin functions as more than a physical barrier: it is an active immune organ. Immune responses in the skin involve an armamentarium of immune-competent cells and soluble biologic response modifiers including cytokines. Traversed by a network of lymphatic and blood vessels, the dermis contains most of the lymphocytes in the skin, other migrant leukocytes, mast cells, and tissue macrophages. Although the epidermis has no direct access to the blood or lymphatic circulation, it is equipped with immune-competent cells: Langerhans cells, the macrophage-like antigen-presenting cells of the epidermis; keratinocytes, epithelial cells with immune properties; dendritic epidermal T lymphocytes, resident cells that may serve as a primitive T-cell immune surveillance system; epidermotropic lymphocytes, migrants from vessels in the dermis; and melanocytes, epidermal pigment cells with immune properties. Although the components of the epidermis and dermis work in concert to execute immune responses in the skin, for purposes of this review, we focus on the cells and cytokines of the epidermal immunologic unit, the frontline of immune protection against environmental toxins and microbes.

Langerhans cells: structure, function and role in oral pathological conditions

Langerhans cells (LCs) are dendritic bone marrow derived cells situated suprabasally in most stratified squamous epithelia, such as the epidermis and the epithelium of oral mucosa, including the gingiva. Langerhans cells are thought to act as antigen-presenting cells (APC) during induction of immune responses. The exact role of Langerhans cells in the oral mucosa is not fully understood although several investigations suggest that these cells are involved in reactions to antigen challenge under both normal and pathological situations. In this paper the structure, phenotypic markers and derivation of Langerhans cells are reviewed. In view of recent findings, the immunological characteristics and the implications of Langerhans cells in pathologic oral reactions are discussed.

T cells expressing the gamma delta T-cell receptor potentiate coxsackievirus B3-induced myocarditis

Initial studies determined whether intraperitoneal (i.p.) injection of BALB/c mice with 0.1, 1.0, and 10 mg of adriamycin (a cardiotoxic anthracycline antibiotic) for times ranging between 1 and 9 weeks prior to i.p. injection of 10(5) PFU of coxsackievirus B3 (CVB3) would alter the severity of virus-induced myocarditis. Prior adriamycin exposure enhanced pathogenicity of a poorly pathogenic CVB3 variant (H310A1) but had no effect on myocarditis produced by the pathogenic variant (H3). Cardiac virus concentrations were equivalent in H3- and H310A1-infected mice irrespective of adriamycin treatment. BALB/c mice treated with either 0.1 ml of complete Freund's adjuvant (CFA), 10 mg of adriamycin, or 10(5) PFU of H3 and H310A1 i.p. developed cytolytic Thy 1.2+ lymphocytes (CTL) to H3-infected myocytes 7 days later. CFA-, adriamycin-, and H3-treated mice developed CTL expressing the gamma delta+ T-cell receptors, while H310A1-infected animals did not. Only H3- and H310A1-infected mice developed alpha beta+ CTL. Treatment of BALB/c mice with 0.1 ml of CFA 5 days prior to H310A1 infection dramatically increased myocarditis. Selective depletion of gamma delta+ T cells abrogated this effect. The ability of gamma delta+ T cells to augment the pathogenicity of H310A1 infection was confirmed by adoptive transfer of CFA-stimulated T cells depleted of either gamma delta- or gamma delta+ cells into H310A1-infected recipients.

Dynamic nature and function of epidermal Langerhans cells in vivo and in vitro: a review, with emphasis on human Langerhans cells

Epidermal Langerhans cells (LC) are Birbeck granule-containing bone-marrow-derived cells, which are located mainly in the suprabasal layer of the epidermis. They can be readily identified by their strong expression of CD1a and MHC class II molecules. In addition to these 'classical' properties, an extensive phenotypic profile of normal human LC, summarized in this review, is now available. The powerful capacity of LC to activate T lymphocytes is clearly documented and, to date, LC are recognized as the prominent antigen-presenting cells of the skin immune system. They are generally believed to pick up antigens encountered in the epidermis and to migrate subsequently from the epidermis to the skin-draining lymph nodes. Upon arrival in the paracortex of lymph nodes, the antigen-laden LC transform into interdigitating cells and they present antigen to naive T lymphocytes in a MHC class II-restricted fashion; this results in the generation of antigen-specific immune responses. It has also been demonstrated that transformation of LC into interdigitating cells occurs when LC are cultured in vitro. Both in vivo and in vitro studies have indicated that properties of LC, such as phenotype, morphology and the stimulatory potential to activate T lymphocytes, are dependent on the local microenvironment in which the LC reside. The essential role of LC in the induction of contact allergic skin reactions and skin transplant rejection is well established.

Immunological signals which control T cell responses

A number of identifiable immunological parameters can influence the elicitation and regulation of antigen-specific inflammatory responses to immunogenic epitopes. Injection of antigen in vivo can lead to the activation of type IV hypersensitivity responses, or to the induction of immunological tolerance to that antigen. We have used the hapten trinitrophenol as a model system for studying the factors which influence the generation and regulation of hypersensitivity responses to immunogenic epitopes in vivo. The generation of hypersensitivity or tolerance to trinitrophenyl depends on a number of immunological factors, including the form of the antigen, the route of immunization, and the presence of immune complexes of antibody and antigen on the surface of the antigen-presenting cell. Immunization with trinitrophenyl resulting in unresponsiveness can be the result of either the inability to prime inflammatory cells in vivo or the induction of suppressor T cells.

Biochemical properties of MHC class II molecules endogenously synthesized and expressed by mouse Langerhans cells

The cell surface expression and biosynthesis of Langerhans cells (LC)-derived major histocompatibility complex (MHC) class II molecules from epidermal cells (EC) prepared freshly and cultured for up to 3 days was investigated. Based on the constitutive expression of MHC class II determinants by LC, a panning and magnetic bead selection procedure was employed, yielding 65% and 86% of I-A+ cells, respectively. Phenotypical and cytochemical examinations revealed that the two LC preparations were free of contaminating macrophages as well as B and T cells. Freshly prepared enriched LC were highly efficient in the stimulation of protein antigen-specific T cell clones, while LC purified from short-term cultured EC suspensions proved to be more efficient allogeneic stimulator cells than fresh LC. Comparative analysis of LC obtained from freshly prepared and from short-term-cultured EC preparations indicated an up-regulation of MHC class II determinants during short-term culture. Radioiodination analysis of LC selected by magnetic beads demonstrated prominent class II alpha and beta chain signals with only a minute fraction of invariant chains p35 and p45 being expressed at the cell surface. Unlike class II complexes derived from B cells, those from LC contained invariant chain fragment p20 in association with alpha/beta heterodimers at the plasma membrane. No qualitative differences between freshly isolated and 3-day cultured LC in cell surface expressed MHC class II components were detectable. Metabolic labeling with subsequent two-dimensional electrophoresis revealed distinct features of LC-derived MHC class II molecules with a high proportion of invariant chains in particular gamma and p40 and their extensive sialylation. While fresh and 1-day cultured LC exhibited appreciable levels of newly synthesized class II molecules, a dramatic down-regulation in class II and invariant chain synthesis was measured after 3 days of continuous in vitro culture.

Cultured epidermal Langerhans cells activate effector T cells for contact sensitivity

To investigate whether Langerhans cells are capable of inducing contact sensitivity effector T cells, we incubated purified T cells from naive mice with syngeneic cultured trinitrophenyl-modified Langerhans cells for 4-5 d. The cells were then expanded in interleukin-2 and fresh medium for another 6-9 d and injected intravenously into naive syngeneic recipient mice. After the ears of recipient mice were painted with 1% trinitrochlorobenzene, we observed an ear-swelling response peaking at 24-48 h. The ear-swelling response was hapten specific. CD8- but not CD4-depleted T cells mediated strong contact sensitivity. Systemic adoptive transfer into nude mice also lead to a hapten-specific delayed ear-swelling response. However, this response was less protracted than in euthymic animals, suggesting the participation of the recipient (non-immunized) T cells in the ear-swelling response of the euthymic mice. Lymphokine analysis of in vitro primed and restimulated T cells revealed predominant production of interleukin-2 but little or no interleukin-4. These in vitro primed cells therefore resemble type 1 or inflammatory T helper cell clones.

Antigen-presenting activity of non-Langerhans epidermal cells in contact hypersensitivity reactions

Despite the critical role of the Langerhans cells in the induction of contact hypersensitivity reactions, non-Langerhans antigen-presenting cells in already sensitized individuals may play a role in the elicitation phase of a contact hypersensitivity reaction. Following epicutaneous challenge with antigens, the number of CD1+DR+ epidermal Langerhans cells increased in a time-dependent way and, concomitantly, CD1-OKM5+DR+ epidermal non-Langerhans cells appeared. In parallel with this, the capacity of epidermal cells to present both alloantigens and auto/nominal antigens increased, and 4 days after initiation of the contact hypersensitivity reactions 33-53% of the epidermal antigen-presenting capacity was due to CD1- non-Langerhans antigen-presenting cells. Thus, contact hypersensitivity skin reactions are accompanied by the appearance of non-Langerhans antigen-presenting cells capable of presenting both alloantigens and auto/nominal antigens.

A cell culture model for T lymphocyte clonal anergy

T lymphocytes respond to foreign antigens both by producing protein effector molecules known as lymphokines and by multiplying. Complete activation requires two signaling events, one through the antigen-specific receptor and one through the receptor for a costimulatory molecule. In the absence of the latter signal, the T cell makes only a partial response and, more importantly, enters an unresponsive state known as clonal anergy in which the T cell is incapable of producing its own growth hormone, interleukin-2, on restimulation. Our current understanding at the molecular level of this modulatory process and its relevance to T cell tolerance are reviewed.

An immunohistochemical and immunoelectron microscopic study of the ontogeny of rat Langerhans cell lineage with anti-macrophage and anti-Ia monoclonal antibodies

An immunohistochemical study with anti-macrophage and anti-Ia monoclonal antibodies was performed to clarify the relationship between Langerhans cells (LC) and indeterminate cells (IC) in rat epidermis both in adulthood and in the fetal stage. On immunoelectron microscopy, a mouse anti-rat macrophage monoclonal antibody, TRPM-1, recently produced by us, reacted with IC and some LC in adult rat skin. Ontogenic study revealed that TRPM-1-positive cells first appeared in the epidermis of fetal rat heads on Day 17 of gestation and then spread caudally along the anterior-posterior axis. On Day 20 of gestation, when the distribution of the TRPM-1-positive cells over body surface became even, Ia-positive cells appeared in the epidermis and began to increase in number. Ia-positive cells with Birbeck granules were found on Day 21 of gestation. These results indicate that. TRPM-1-positive IC matured into Ia-expressing LC after being exposed to microenvironmental change during the perinatal period. The number of Ia-positive cells exceeded that of TRPM-1-positive cells at around 5 d after birth. Afterwards, there were more dendritic Ia-positive cells found in the interfollicular areas than TRPM-1-positive ones. However, local concentrations of the TRPM-1-positive IC in the follicular infundibula were frequently found in the fetal stage and occasionally in adulthood. These TRPM-1-positive cells in the follicular infundibula were thought to be a precursor pool in the epidermis for LC.

Optimization of an in vitro lymphocyte blastogenesis assay for predictive assessment of immunologic responsiveness to contact sensitizers

Current methods for the predictive and diagnostic assessment of contact sensitization rely on the visual scoring of skin reactions. Predictive animal tests, generally using guinea pigs, require a relatively large number of animals to produce a sufficient database for interpreting skin reaction scores. In vitro assays have the potential of being more quantitative than skin testing and, if so, would require fewer animals. However, although in vitro assays are commonly used to study the cellular immune response to strong contact sensitizers, there has been little effort to validate them for predictive assessment purposes. We have optimized an in vitro lymphocyte blastogenesis assay for detecting the response of mouse lymphocytes to strong contact sensitizers with the eventual objective of applying this assay to moderate and weak sensitizers as well. Lymph node lymphocytes from mice sensitized to the strong contact allergens, dinitrochlorobenzene (DNCB), dinitrofluorobenzene (DNFB), or trinitrochlorobenzene (TNCB), responded [greater than or equal to 12,000 counts per minute (CPM) above background] when cultured with water soluble chemical analogues, di- or trinitrobenzene sulfonic acid (DNBS or TNBS). However, the strong sensitizer, oxazolone (OXAZ), has no water soluble analogue and lymphocytes from mice sensitized to OXAZ responded poorly in vitro (less than 2000 CPM) to an ethanol-solubilized OXAZ preparation in spite of very strong in vivo sensitization (ear swelling assay). To increase the assay sensitivity, for OXAZ, we modified the antigen presentation conditions by using 1) solubilized antigen-modified adherent spleen cells, 2) dendritic cells from the draining lymph nodes of antigen painted mice, and 3) antigen-modified Langerhans cell-enriched cultured epidermal cells (EC). These approaches increased OXAZ-directed responses to greater than 7000, greater than 20,000, and greater than 100,000 CPM, respectively, under culture conditions optimized for cell density, responder: stimulator cell ratio, culture duration, and responder cell type. Our results represent a first attempt to directly modify cultured epidermal cells with OXAZ and use these cells to stimulate OXAZ-directed blastogenesis in microtiter plate cultures. This optimized assay is now under evaluation for predictive assessment of contact sensitizers relevant to occupational and consumer exposures.

Dendritic cells and T cells transfer sensitization for delayed-type hypersensitivity after skin painting with contact sensitizer

The cells involved in the development of delayed-type hypersensitivity (DTH) to the contact sensitizer fluorescein isothiocyanate (FITC) were examined. Cells used for transferring sensitization were obtained from donor mice up to 5 days following skin painting with FITC. Recipient mice were sensitized by footpad injections of dendritic cells (DC) obtained from donor lymph nodes up to 3 days following skin painting, when DC expressed high levels of antigen. DTH, assessed by ear swelling 24 hr following ear challenge with FITC, was detected when recipient mice were challenged 5 days after transfer of DC, but not when ear challenged immediately after transfer. Removal of donor DC using the cytotoxic antibody 33D1, plus complement, either from the DC-enriched population or from whole lymph node cells 24 hr after skin painting, abolished the capacity to transfer DTH. Purified T lymphocytes obtained from donor mice between Days 3 and 5 after skin painting, transferred DTH when recipients were ear challenged with FITC 5 days after footpad injections. DTH also occurred in mice ear challenged with antigen immediately after receiving footpad injections of either normal or irradiated T cells obtained from donors 4 days after skin painting. B cells and macrophages did not transfer sensitization for DTH throughout the time-course. Therefore an early stage in the immune response, where antigen-bearing DC initiated DTH, was distinguished from a later stage, where T cells transferred sensitization.

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.

Photoimmunology: the mechanisms involved in immune modulation by UV radiation

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

Down-regulation of suppressor cell induction

A unidirectional cascade of cell interactions has been described previously that involves at least three distinct populations of suppressor T cells (Ts) that interact in appropriate succession to mediate suppression of delayed hypersensitivity responses to the 4-hydroxy-3-nitrophenylacetyl hapten (NP). The present work focuses on the potential bidirectional effects of one suppressor factor and how it can regulate the homeostatic mechanisms that maintain this suppressor cell cascade. Specifically, the effects of prior administration of mice with a transducer suppressor factor (TsF2) on the generation of NP-specific TS1 suppressor cells were evaluated. It was observed that the TSF2 given 2-14 days prior to administration of the tolerogen (NP-coupled splenic-adherent cells) interfered with the development of inducer TS1 suppressor cells. This down-regulation of suppressor cell induction is mediated by a population of cells that have the following characteristics: NP-binding, Lyt-1+2-, L3T4+, I-J+, and Vicia villosa (VV)-adherent T cells (for convenience these cells are termed anti-suppressor cells). Furthermore, there are genetic restrictions (both H-2 and IgH) between TSF2 and host which control the generation of anti-suppressor cells. The results suggest that TSF2 may have a role in homeostatic mechanisms that regulate the NP-specific suppressor cell cascade. The relationship of anti-suppressor and contra-suppressor cells is discussed.

Ultrastructural changes in epidermal Langerhans cells and melanocytes in response to ultraviolet irradiation, in Australians of Aboriginal and Celtic descent

The effects of exposure to small doses of artificial ultraviolet radiation (UVR) on the ultrastructure of epidermal Langerhans cells (LC) and melanocytes were studied in two groups of Australian subjects, one of Aboriginal and the other of Celtic descent. UV exposure induced an apparent depletion of LC in the epidermis of both groups. However, LC depletion in the Aboriginal subjects was associated with apoptosis, whereas organelle and membrane disruption in the LC of Celtic subjects suggested a reduction by direct cellular damage. LC in Aboriginal epidermis tended to become relocated at more superficial levels following UV exposure, and their Birbeck granules became more numerous. LC in Celtic epidermis appeared to become relocated in a basal location and contained fewer Birbeck granules. The central lamina of the Birbeck granules in Aboriginal LC, which was more electron-dense than that in Celtic subjects prior to UV treatment, was temporarily lost following treatment, while the ultrastructure of Birbeck granules in Celtic LC was unchanged. LC and 'indeterminate cells' in intimate association with lymphocyte-like cells occurred in the basal layer of Celtic epidermis 5 days after exposure. These complexes were not observed in Aboriginal epidermis although isolated lymphocyte-like cells were observed in the same location. Melanocytes in Aboriginal epidermis contained greater numbers of melanosomes than those in Celtic epidermis throughout the experiment. Inactive epidermal melanocytes in Celtic subjects initially responded to UV exposure with a slight increase in melanosome content followed by a substantial further increase, whereas active melanocytes in the Aboriginal subjects showed the opposite response. The implications of the different responses of LC and melanocytes in the two groups, in relation to immunological function of the epidermis and the marked racial difference in the incidence of skin cancer, are discussed. Cancer of the skin, particularly basal and squamous cell carcinoma, occurs primarily in people with fair skin who burn easily following exposure to ultraviolet radiation (UVR). In contrast, the incidence of skin cancer in inherently dark-skinned people is low. Melanin is synthesized by melanocytes in response to UVR and is thought to protect epidermal cells against damage to their genetic material by absorbing UVR and thereby reducing its penetration into the skin. Thus darkly pigmented skin is more resistant to the effects of UVR.(ABSTRACT TRUNCATED AT 400 WORDS)

Highlights of contemporary research on host immune responses to ticks

Host immune responses to ticks have been known since the early part of this century. This research has emanated from throughout the world with the most detailed studies originating from Australia and the United States. A review of all the studies to date indicates a diverse tick species list consisting primarily of Ixodid ticks, but a few Argasid species have been examined. Typically, research on this topic during the first half of this century has utilized the bovine host, whereas research over the past 20 years has concentrated on the rodent host. The emphasis of this research has been to define host resistance in terms of behavioral and physiological changes in the host, accompanied by changes in the feeding and reproductive potential of the ticks. The primary objective of this research is to develop an innovative tick control strategy that will allow greater and safer control than that afforded by acaricides. This paper highlights the study of host immune responses to ticks over the century to date. However, owing to the great growth in the fields of immunology and molecular biology, the greatest gains have been made from 1970 to 1985. Therefore, the emphasis of this review is on research reported during the last 15 years.

Sex differences in regulation of contact sensitivity reaction in mice. 1. Influence of sex on the generation of contrasuppressor and afferent suppressor cells

It is well known that humoral and cell-mediated immune responses are better in females than in males. Females also develop autoimmunity more easily than males. Contact sensitivity, one of the forms of cell-mediated immunity, is controlled at the afferent and efferent phases by complex interactions of regulatory T cells. Our present experiments indicate that T suppressor afferent (Ts-aff) and T contrasuppressor cells (Tcs) are generated in the mouse in a sex-dependent fashion. These two types of regulatory cells are induced by antigen-antibody complexes containing various immunoglobulin isotypes. Females require fewer antigen (Ag)-IgG1 complexes to produce Tcs cells, but more Tcs cells after antigenic stimulation in females tips the balance toward better immune responsiveness. It remains to be established whether the peculiarities in generation of regulatory cells in female mice are relevant to the pathogenesis of autoimmune diseases which predominantly affect females.

Localization of antigen on lymph node dendritic cells after exposure to the contact sensitizer fluorescein isothiocyanate. Functional and morphological studies

We have examined the cells involved in the development of contact sensitivity to FITC in CBA mice. After skin painting with antigen, the number of dendritic cells (DC) in the draining lymph nodes increased by 30 min, was maximal at 48 h, and returned to normal by 6 d. Derivation of some DC from Langerhans' cells of the skin was indicated from the presence of Birbeck granules observed in some DC isolated 24 h after skin painting. The DC acquired FITC and by 8 h there were two populations, one highly fluorescent and the other less fluorescent. The highly fluorescent cells were present between 8 h and 3 d after sensitization, and during this period the DC were potent at initiating primary proliferative responses of normal syngeneic T lymphocytes in vitro. Between days 3 and 5 the numbers of lymphocytes in the draining lymph node increased. During this period purified T lymphocytes did not express detectable levels of antigen, but enriched B cell populations expressed antigen transiently on day 1, 2, or 3 after exposure to antigen. The results showed that, during a 3-d period after exposure to antigen, DC expressed antigen and stimulated T cell proliferation. We speculate that low amounts of FITC binding selectively to veiled cells or lymph node DC in the first hours after exposure to antigen are not immunogenic but that Langerhans' cells acquire high levels of antigen, enter the nodes, and initiate immune responses.

Induction of sensitization and tolerance in contact sensitivity with haptenated epidermal cells in the guinea-pig

Haptenated murine Langerhans' cells (LCs) have been reported to induce contact sensitivity when injected via the subcutaneous, intraperitoneal and, in some instances, the intravenous route. Similar studies were undertaken to elucidate the role of the LC in the induction of contact sensitivity in the guinea-pig. The subcutaneous injection of dinitrophenylated epidermal cells induced hapten-specific contact sensitivity in a dose-dependent fashion. This contrasts with the tolerance that was induced by the intravenous or intraperitoneal injection of similarly haptenated cells. Contact sensitivity by haptenated epidermal cells could be induced in syngeneic and allogeneic recipients and did not require the transfer of viable cells. Using the monoclonal antibody MSgp2, which detects LCs, LC-enriched and LC-depleted populations were prepared by an 'indirect antibody' panning technique. It was found that a haptenated LC-depleted epidermal cell population (0.1% LC) induced the same degree of contact sensitivity or tolerance, depending on the route of immunization, as a haptenated 'freshly isolated' epidermal cell population (1% LC). Whereas, a purified population of haptenated LC (85-90%) induced no significant degree of contact sensitivity or tolerance. These results confirm our previous conclusions based the in vivo depletions of Langerhans' cells, and suggest that the epidermal Langerhans' cell is not essential for the induction of contact sensitivity in the guinea-pig. However, this does not exclude the possibility that the LC is involved in the elicitation of contact sensitivity in a sensitized animal.

Abrogation of the lethal graft-vs.-host reaction developed to non-H-2 antigens: involvement of T suppressor cells distinct from veto cells

The mortality induced by graft-vs.-host reaction (GVHR) in (DBA/2 x B10.D2)F1 recipients transplanted with cells from H-2d-identical B10.D2 donors can be abrogated by preimmunizing the donors with parent-strain spleen cells from normal DBA/2 mice. The experiments described here were designed to explore the possibility that the observed protection might be mediated by veto cells contained in the immunizing cell inoculum; the reasoning was based on an analogy with the cytotoxic T lymphocyte response to non-H-2 antigens where suppression can be mediated by veto cells, present in the spleens of normal mice, which are radiosensitive and largely Lyt-2+. We show that the intensity of the protection against GVHR mortality is a function of the immunizing cell dose, and that protection remains effective when optimal doses of immunizing cells are (a) irradiated or (b) pretreated with anti-Thy-1 serum. GVHR suppression is abrogated when, before transfer to F1 recipients, suppressor cells from spleens of immunized donors are pretreated with antiserum directed against Lyt-1.2 (expressed by B10.D2 but not by DBA/2, which expresses Lyt-1.1); in contrast, it is not significantly affected when these same cells are pretreated with anti-Lyt-2.2 alloantiserum. We conclude that when the antigen load is great enough the immunizing cells play a largely passive role in the observed suppression. The protection against GVHR mortality seen in this H-2-compatible combination is transferable by Lyt-1+2- suppressor T cells originating in mice given high doses of alloantigen. These suppressor cells are therefore distinct from the splenic veto T cells effective against cytotoxic T lymphocyte responses to non-H-2 antigens. The mechanism of the observed suppression and its relationship to Mls product(s) are discussed.

Dose response and time course for induction of T6- DR+ human epidermal antigen-presenting cells by in vivo ultraviolet A, B, and C irradiation

In vivo ultraviolet (UV) exposure of human skin abrogates the antigen-presenting function of T6+ DR+ Langerhans cells and induces the appearance of antigen-presenting T6- DR+ epidermal melanophages. UV-exposed epidermal cells containing T6- DR+ epidermal antigen-presenting cells, in contrast to unexposed epidermal cells containing T6+ DR+ Langerhans cells, potently activate autoreactive regulatory T cells in the absence of exogenous antigens. Autoreactive T cells may be important for regulation of other immune responses such as those which occur in photosensitive lupus erythematosus and in immune surveillance of UV-induced skin cancers. It is therefore imperative to determine the factors that govern their appearance in the skin. It was found that UVB and UVC, but not UVA, induced a dose-dependent appearance of T6- DR+ epidermal melanophages. The optimal time of appearance was 2 or 3 days after UVB and UVC exposure. In contrast, UVA was a poor inducer of T6- DR+ cells at all doses and all time points tested. Although UVA was a poor inducer of T6- DR+ epidermal cells, UVA radiation resulted in depletion of T6+ DR+ Langerhans cells from the epidermis, as did UVB and UVC radiation. This differential effect of UV wave bands on the immunocompetent cells in human skin may be related to the greater potential of UVB exposure to induce skin cancers and to exacerbate systemic lupus erythematosus.