The accessory function of B lymphocytes is resistant to the adverse effects of UV radiation

Treatment of cutaneous T cell lymphoma with extracorporeal photopheresis induces Fas-ligand expression on treated T cells, but does not suppress the expression of co-stimulatory molecules on monocytes

Following extracorporeal photopheresis (ECP), lymphocytes become apoptotic and upregulate class I MHC antigenic peptides. Conversely, ECP treated monocytes demonstrate activation markers and have an increased avidity for the phagocytosis of apoptotic T cells. Processing of apoptotic T cells by monocytes, following ECP, is thought to induce an immunomodulatory response, which targets untreated, but clonal T cells. Recently we detected apoptotic lymphocytes immediately post ECP. Although enhanced CD95 (Fas) expression has been observed 24 h post ECP, CD95 and Fas-ligand (Fas-L) expression have not been determined at this very early apoptotic stage. Exposure of monocytes to UV has previously suppressed expression of the co-stimulatory molecules required for the presentation of processed antigens to T cells. Our data demonstrate no increase in CD95 or Fas-L expression on T cells tested immediately following ECP. However, the number of T cells expressing Fas-L significantly increased 24 h post ECP (P<0.005). The expression of the co-stimulatory molecules, CD54, CD80 and CD86, remained unaltered on monocytes treated by ECP. Although the mechanism responsible for early induction of lymphocyte apoptosis remains unclear, the later apoptosis involves Fas-L expression. The maintenance of co-stimulatory molecules, on treated monocytes, indicates that they retain the ability to induce an immunomodulatory response.

ICAM-1 mRNA levels and relative transcription rates are decreased by UV irradiation of monocytes

We have previously demonstrated that in vitro exposure of antigen-presenting cells to UVB radiation inhibits their ability to activate T cells through selective effects on the expression of the adhesion molecule ICAM-1 (intercellular adhesion molecule-1). Intercellular adhesion molecule-1 is an important costimulatory molecule provided by antigen-presenting cells for T-cell activation. Using human peripheral blood monocytes and the U937 human monocytoid cell line as model antigen-presenting cells, we investigated the effect of UV radiation on the mRNA steady-state levels for human ICAM-1 by northern blot analysis and relative transcription rates of ICAM-1-specific mRNA by nuclear run-on assay (NRO). Northern blot analysis demonstrated a decreased level of ICAM-1 mRNA at 4 h postradiation relative to glyceraldehyde-3-dehydrogenase mRNA. The NRO analysis demonstrated a greater than 35% decrease of newly synthesized specific mRNA at 4 h postirradiation. The results demonstrate a transcriptionally based mechanism for the diminution of both mRNA and translatable mRNA specific for ICAM-1 regulation in UV-treated antigen-presenting cells.

UV-induced cutaneous photobiology

Ultraviolet radiation (UVR) present in sunlight is a major environmental factor capable of affecting human health and well being. The organ primarily affected by UVR is the skin, which is composed of a variety of different cell types. Here, UVR is needed for production of active vitamin D as well as producing undesirable effects such as sunburn, premature cutaneous photoaging, and promoting skin cancer development. Depending on the radiation dose, UVR influences virtually every cutaneous cell type investigated differently. Since the end of the nineteenth century, sun exposure has been known to induce skin cancer, which is now the human malignancy with the most rapidly increasing incidence. In several experimental models, mid-range UVR has been demonstrated to be the major cause of UV-induced cutaneous tumors. The stratospheric ozone layer protecting the terrestrial surface from higher quantum energy solar radiation is being damaged by industrial activities resulting in the possibility of increased UVR exposure in the future. Investigations in the field of experimental dermatology have shown that within the skin an immunosurveillance system exists that may be able to detect incipient neoplasms and to elicit a host responses against it. This article reviews the literature on studies designed to investigate the effects of UVR on cutaneous cellular components, with special focus on the immune system within the skin and the development of UV-induced cancer.

Molecular, metabolic and immune evidence suggest that systemic autoimmune disease is antigen-mediated

Patients with systemic lupus erythematosus generate a sustained immune response against self. The tools of modern molecular biology have been applied to cell activities and elements/signals of the immune system, but a structural or regulatory defect has not been found. When deoxyribonucleic acids for autoantibodies were cloned and sequenced, they were like other autoantibody DNA sequences; when genetic materials for autoantibodies were inserted into transgenic mice, cells secreting the antibodies were subject to normal control mechanisms and eliminated. A failure to clear self-reactive antibody producing thymocytes has not been demonstrated in human systemic lupus erythematosus. Molecular analyses of the efferent side of the immune response have been largely normal in systemic lupus erythematosus. The structure of autoantibodies suggests that they have been generated by selection pressures and the presence of endogenous antigens. If the immune system attack on self was secondary, structural changes and metabolic reactions capable of generating antigens should be found in systemic lupus erythematosus cells. Structural changes have been found in deoxyribonucleic acid from phytohaemagglutinin-stimulated systemic lupus erythematosus lymphocytes in the form of S1 nuclease-sensitive deoxyribonucleic acid breaks. Altered cellular macromolecules could result from endogenous metabolic processes, particularly oxygen free radicals and arachidonic acid metabolites. Excess free-radical species, generating positive nitroblue tetrazolium-reacting material and positive chemiluminescence, have been found in most but not all phytohaemagglutinin-stimulated lupus lymphocyte samples. If endogenous metabolic processes act on endogenous deoxyribonucleic acid, endogenous cell DNA breakdown may lead to low molecular weight deoxyribonucleic acids and deoxyribonucleic acid/immune complexes in systemic lupus erythematosus sera that are potentially immunogenic. These combined findings suggest that the exaggerated immune responses of systemic lupus erythematosus may be a normal response to protect the host from a perceived antigenic threat.

Reduced antigen-presenting function of human Epstein-Barr virus (EBV)-B cells and monocytes after UVB radiation is accompanied by decreased expression of B7, intercellular adhesion molecule-1 (ICAM-1) and LFA-3

In this study, the effect of ultraviolet-B (UVB) radiation on antigen-presenting function was studied, to investigate whether antigen-presenting cells (APC) are inhibited by UVB through a common mechanism. Two types of human APC were used: EBV-B cells and monocytes, and these were irradiated in vitro with single low doses of UVB (range 0-200 J/m2). Irradiation of EBV-B cells or monocytes resulted in similar dose-dependent reduction in APC function, when determined by the allogeneic mixed leucocyte reaction (MLR) or Candida albicans- or tetanus toxoid-specific T cell response. Our study shows that the reduced APC function was not likely to be caused by alterations in antigen processing or cytokine production. However, UVB-irradiated APC displayed marked changes in adhesion molecule expression. Irradiated EBV-B cells showed reduced expression of ICAM-1 (30%), LFA-3 (25%) and B7-1 (35%), while expression of HLA-DR, CD19 and LFA-1 was not affected. UVB irradiation of monocytes did result in reduction in the expression of HLA-DR (30%), LFA-3 (40%), ICAM-1 (65%) AND B7-1 and B7-3 (90%), but had no effect on CD14, LFA-1 and ICAM-3 expression. Addition of non-irradiated cells (but not the supernatant of these cells) or CD28 antibodies partly restored T cell activation, indicating that UVB-induced reduction in APC function is at least partly mediated via impairment of co-stimulatory molecule expression.

Effect of storage and ultraviolet B irradiation on CD14-bearing antigen-presenting cells (monocytes) in platelet concentrates

BACKGROUND

Ultraviolet B (UVB) irradiation of platelet concentrate (PCs) reduces platelet alloimmunization, but the mechanism of the effect is unclear. Evidence suggests that UVB may downregulate the expression of surface adhesion molecules on passenger antigen-presenting cells in PCs.

STUDY DESIGN AND METHODS

The effect of blood bank storage, platelet preparation from whole blood, and UVB irradiation on the quantitative expression of intercellular adhesion molecule-1 (ICAM-1, or CD54), HLA-DR, CD45, and CD11c on CD14-positive antigen-presenting cells (monocytes) was studied by using two-color flow cytometry.

RESULTS

Blood bank storage for 4 days resulted in upregulation of ICAM-1 and HLA-DR and downregulation of CD14 but left the expression of CD11c and CD45 unchanged. Preparation of PCs from fresh whole blood was associated with a rapid increase in CD11c without upregulation of ICAM-1 and HLA-DR. UVB irradiation before storage inhibited the upregulation of ICAM-1 and HLA-DR, resulted in accelerated downregulation of CD14, and was associated with increased loss of monocytes. Agitation of the PC bag during irradiation was of critical importance, since omission of agitation resulted in largely uninhibited upregulation of ICAM-1 but was still associated with significantly higher cell loss than that seen in unirradiated controls.

CONCLUSION

UVB exposure nonspecifically affects monocytes in PCs, resulting in downregulation of surface molecules that are important for antigen presentation, as well as in significant cell loss.

Accessory cell ability of Langerhans cells for superantigen is resistant to ultraviolet-B light

We examined the effects of ultraviolet-B (UVB) irradiation on the accessory cell ability of Langerhans cells (LC) to induce a T-cell response to a superantigen, staphylococcal enterotoxin B (SEB). The ability of LC-enriched epidermal cells (LC-EC) to evoke a T-cell response to SEB was retained at the doses of UVB (up to 40 mJ/cm2) that profoundly affected the antigen-presenting function of LC-EC for a hapten, trinitrophenyl (TNP), and a protein antigen, conalbumin. Thus, the LC accessory function for superantigens is more resistant to UVB irradiation than that for ordinary antigens. This UVB resistance is presumably due to no requirement of antigen processing for superantigens as chemically fixed or chloroquine-treated LC-EC still retained their ability to induce T-cell responses to SEB. Higher doses of UVB (more than 60 mJ/cm2) reduced the accessory cell ability of LC-EC for SEB up to 50% of control. The addition of monoclonal antibodies against adhesion molecules between LC and T cells to the culture resulted in a substantial suppression of the T-cell response to SEB induced by nonirradiated LC-EC, while the UVB-irradiated LC-EC-induced T-cell response was not significantly blocked with these monoclonal antibodies. This suggested that the reduction of LC ability for superantigen by high doses of UVB is at least partly due to the impairment of adhesion molecules on LC by UVB irradiation.

Predominance of epidermal CD8+ T lymphocytes in bullous cutaneous reactions caused by beta-lactam antibiotics

The phenotype and functional characteristics of skin-infiltrating lymphocytes in beta-lactam antibiotic-induced vesiculobullous exanthemas were studied in vivo and in vitro. Immunohistochemical analysis demonstrated that CD8+ T lymphocytes were the predominant epidermal T-cell subset in these reactions. Epidermal T lymphocytes were isolated and expanded for in vitro studies. Fluorescence-activated cell sorter analysis showed the majority of epidermal T cells to be CD3+, T-cell receptor alpha/beta+, CD4-, CD8+, and HLA-DR+, which correlated with the predominance of epidermal CD8+ T lymphocytes found in situ. Three CD8+ epidermal T-cell clones derived from cutaneous lesions proliferated in response to penicillin-pulsed autologous antigen-presenting cells but not allogeneic antigen-presenting cells, indicating that those clones were antigen and major histocompatibility complex specific. All T-cell clones produced significant amounts of interleukin-2, interferon-gamma, and granulocyte-macrophage colony-stimulating factor. Additionally, the T-cell clones displayed cytotoxicity against epidermal cells in lectin-mediated cytotoxicity and against B-cell lines in T-cell receptor-triggered cytotoxicity. These data demonstrate the presence of epidermal drug-specific CD8+ T cells in bullous drug reactions. Because these CD8+ T cells have a cytotoxic potential, they may contribute to the necrosis of keratinocytes associated with drug-induced blister formation.

Ultraviolet irradiation inhibits killer-target cell interaction

The effects of ultraviolet (UV) irradiation on cell-mediated cytolysis were examined in order to clarify the inhibitory mechanisms of allosensitization by UV irradiation. UV-B-irradiated target cells (Sa; an Epstein-Barr virus-transformed B cell line) exhibited more resistance against alloreactive cytotoxic T lymphocytes (CTL) than mitomycin C (MMC)-treated target cells. In the conjugate formation assay, UV-B-irradiated target cells showed a considerably lower binding to alloreactive CTL than MMC-treated target cells. UV-B irradiation induced a reduction of HLA-class I, -DR, CD54 (ICAM-1) and CD58 (LFA-3) expression on target cells. However, it does not seem to contribute to the inhibition of cell adhesion induced by UV-B irradiation because a similar reduction of cell surface antigens was observed in MMC-treated target cells. Number of cells capped with anti-HLA-class I, -DR, CD54 or CD58 monoclonal antibody were markedly reduced by UV-B irradiation compared to that by MMC treatment. These findings suggest the possibility that the inhibition of cell adhesion between UV-B-irradiated Sa target cells and alloreactive CTL is due to the impaired mobility of cell surface antigens which will affect the early process of cell-mediated cytolysis.

Modulation of interferon-gamma-induced HLA-DR expression on the human keratinocyte cell line SCC-13 by ultraviolet radiation

Cell surface expression of major histocompatibility determinants on epidermal keratinocytes is a characteristic feature of a number of inflammatory dermatoses and in all likelihood is caused by diffusion of human leukocyte antigen (HLA)-DR-inducing cytokines from cells present in the dermal mononuclear cell infiltrate. Many of these same disorders respond to ultraviolet (UV) radiation phototherapy. Using the human SCC-13 keratinocyte cell line as a model, UV radiation was found to inhibit interferon-gamma-induced HLA-DR expression. Inhibition correlated closely with decreased steady-state levels of HLA-DR mRNA. These findings provide evidence that the therapeutic effect of UV radiation phototherapy may be mediated by its capacity to down-regulate cytokine-induced keratinocyte HLA-DR expression.

Ultraviolet B-irradiated antigen-presenting cells display altered accessory signaling for T-cell activation: relevance to immune responses initiated in skin

A principal mechanism by which ultraviolet (UV) B radiation exerts its selective and antigen-specific suppressive influence on immune responses is through its effects on the capacity of antigen-presenting cells (APC) in skin, primarily Langerhans cells (LC), to differentially activate T-cell subsets. Recent evidence has indicated that LC, following UVB radiation, lose the capacity to stimulate proliferation of CD4+ Th1, but not of Th2, clones. Additional work has shown this acquired unresponsiveness of Th1 cells to represent a long-lasting form of clonal anergy that results from a block in their ability to produce IL-2. Although not completely delineated, these defects appear to be the result of preserved delivery of the primary signal transduced by interaction of the MHC/antigen complex on APC with the T-cell receptor complex, in the absence of a viable second signal normally delivered by interaction of a co-stimulatory factor from APC with its appropriate ligand on the T cells. These findings support the notion that the outcome of certain immune responses depends greatly upon conditions that are brought to bear on APC and T cells during the time of antigen presentation.

Ultraviolet-irradiated monocytes efficiently inhibit the intracellular replication of Mycobacterium avium intracellulare

The purpose of this study was to evaluate the effect of ultraviolet (UV) radiation on the antimicrobial activities of monocytes for the intracellular pathogen Mycobacterium avium intracellulare (MAI). UV radiation augmented monocyte antimicrobial activity for MAI in a dose-dependent fashion. UVB doses of greater than or equal to 25 J/m2 resulted in a 50-100-fold reduction in MAI growth 7 d after initiation of culture. The increased monocyte antibacterial effect could be blocked by a plate glass filter, indicating that wavelengths within the UVB were responsible for the effect. UV radiation did not stimulate monocyte phagocytosis, and enhanced inhibition of MAI growth was observed in populations of adherent mononuclear cells that were devoid of T cells. This suggested that UV radiation acted directly to augment intrinsic monocyte antimicrobial activities. The administration of 8-methoxypsoralen plus UVA radiation to monocytes also augmented their antimicrobial activities against MAI. UV radiation thus may serve as a unique agent by which to evaluate the mechanisms by which mononuclear phagocytes control the growth of MAI.