Effect of orally administered aromatic retinoid on murine Langerhans cells

All-trans retinoic acid induces functional maturation of epidermal Langerhans cells and protects their accessory function from ultraviolet radiation

Retinoids provide some protection against ultraviolet radiation-induced skin damage. We have previously shown that topical all-trans retinoic acid prevents ultraviolet light from reducing the density of epidermal Langerhans cells in the epidermis but does not inhibit the development of immunosuppression to a locally applied contact sensitizer. We therefore investigated the ability of all-trans retinoic acid to modulate Langerhans cell induction of allogeneic T-cell proliferation in the mixed epidermal cell lymphocyte reaction. Langerhans cells isolated from all-trans retinoic acid-treated mice induced an enhanced mixed epidermal cell lymphocyte reaction. This is similar to Langerhans cells cultured with granulocyte-macrophage colony stimulating factor. Retinoic acid treatment also enhanced the allogeneic cell-stimulating capability of Langerhans cells isolated from ultraviolet-irradiated mice. Langerhans cells from all-trans retinoic acid-treated, ultraviolet-irradiated mice which were "matured" by 3 days in culture induced a larger mixed epidermal cell lymphocyte reaction than mice treated with solvent and ultraviolet irradiation. Thus all-trans retinoic acid treatment of mice causes Langerhans cell maturation and inhibits ultraviolet light from reducing their density or impairing their allogeneic cell-stimulating capacity. However, these mice remained immunosuppressed upon application of a contact sensitizer to irradiated or unirradiated skin. It is thus likely that, whereas all-trans retinoic acid protects local Langerhans cell numbers and function, it does not inhibit the production of an ultraviolet radiation-induced photoproduct which causes immunosuppression.

Role of Langerhans cells and other dendritic cells in viral diseases

Langerhans cells are part of a vast system of potent antigen-presenting cells known under the name of dendritic cells. During the last decade, much has been learned on dendritic cell involvement in the immune response to infectious diseases. This review briefly summarizes our current understanding of the role played by Langerhans cells and other dendritic cells in the pathogenesis of DNA and RNA virus infections. These data may form the basis for the development of innovative approaches in the diagnosis, prevention, and treatment of viral diseases.

Differential effects of cyclosporine and etretinate on serum cytokine levels in patients with psoriasis

BACKGROUND

The in vivo effects of cyclosporine and etretinate on the immune system are still unclear.

OBJECTIVE

Our purpose was to determine the effects of these drugs on in vivo production of various cytokines.

METHODS

Serum cytokine levels were measured sequentially by radioimmunoassay in psoriasis patients treated with either cyclosporine or etretinate.

RESULTS

Interferon-gamma levels were initially elevated and rapidly returned to baseline levels before clinical improvement in both treatment groups. A transient increase before the relapse was also observed in some patients. Etretinate treatment resulted in a substantial decrease in tumor necrosis factor-alpha levels, whereas an unpredictable increase was found during the late phase of cyclosporine treatment.

CONCLUSION

The in vivo effects of antipsoriatic drugs on cytokine production are different from those demonstrated in vitro. Measurement of serum cytokine levels is useful for monitoring patients with psoriasis.

Sequence of morphological events during topical application of retinoic acid on the rhino mouse skin

In a study of the comedolytic action of retinoids on the epidermal pseudocomedones of rhino mouse skin, the earliest changes and the sequence of events induced by the treatment were investigated. Rhino mice were treated topically with all-trans retinoic acid and at various time intervals from day 0 to 3 weeks, histological and ultrastructural studies as well as quantification of mast cells were performed. The earliest changes occurred in the dermis after 2 days of treatment and were characterized by degranulation of mast cells, clumping and association of Langerhans cells and lymphocytes. During the second week of treatment there was hyperplasia, hypergranulosis and an increase in the number of membrane coating granules with disorganization of the horny layer both of the epidermis and the follicular epithelium. These changes in the proliferation and the differentiation of keratinocytes resulted in a comedolytic effect. Associated with these epidermal changes there were changes in the dermis with an increased number of mast cells and a decreased number of Langerhans cells.

Mouse footpad Langerhans cells as an indicator for safety of foot and mouth disease virus vaccines

The effect of various vaccines against foot and mouth disease virus (FMDV) was tested on Langerhans cell density in the footpad epidermis of mice. Injection of monovalent, bivalent and trivalent FMDV vaccines caused a reduction in Langerhans cell density in the murine skin, which was more marked at the center of the footpad, the site of injection, than at the periphery. Testing of the various components of the vaccine showed that saponin caused a marked reduction in Langerhans cells while injection of aluminium hydroxide had a lesser effect and the virus alone had no effect on these cells. Thus Langerhans cell density could serve as an efficient marker to test the safety of vaccines to FMDV since the integrity of Langerhans cells, which are the antigen-presenting cells in the skin epidermis, is needed for an effective immune response to the vaccine.

Rationale for anti-AIDS chemotherapy directed at HIV-1 infected dendritic cells in seropositive individuals prior to the appearance of ARC and AIDS

An approach to anti-AIDS chemotherapy is presented from the point of view of treating seropositive individuals by eliminating the infected dendritic cells that are the in vivo target of HIV-1. Special attention is given to the treatment of Langerhans (dendritic) cells in the skin and epithelia that are infected in vivo by HIV and are involved in the development of the symptoms leading to AIDS and ARC. Since HIV is released through the cervical and vaginal epithelia in seropositive women, it is suggested that combined local treatment of vaginal epithelium with steroids that inactivate dendritic cells and azidothymidine (AZT) that inhibits HIV-1 replication might prevent virus dissemination. Abrogation of HIV-1 transmission will help to prevent its spread throughout the heterosexual population. Thus a new rationale for anti-AIDS treatment is presented, namely selective elimination of HIV-1 infected dendritic cells in the skin and epithelia of infected individuals before the appearance of ARC or AIDS. Subsequent restoration of dendritic cells in HIV-1-infected persons (and in AIDS patients) by means of orally administered retinoids in combination with an antiviral drug might be a useful approach to prevent or delay AIDS.

Langerhans cell density and activity in mouse skin and lymph nodes affect herpes simplex type 1 (HSV-1) pathogenicity

Langerhans cells are epidermal antigen-presenting cells that function by taking up antigens in the skin, migrating to the lymph nodes, where they are designated interdigitating cells, and triggering the immune response. The role of interdigitating cells (IDC) was investigated in a murine model of herpes simplex virus-1 infection in the skin. The number of IDC in the lymph nodes began to increase on the first day following infection and reached a peak three days p.i. Low titers of infectious virus were recovered from the fraction of lymph node cells that consisted of 60-80% IDC at one day p.i. Lymph node cells that were obtained from mice immunized with HSV-1 proliferated in vitro in response to viral antigens but did not respond to mock antigens. When mice were immunized with HSV-1 inoculated into skin that had been depleted of Langerhans cells, this in vitro proliferative response was abolished. Thus, the present results suggest that Langerhans cells function in the immune defense of the skin against HSV-1 infection by transporting the virus to the peripheral lymph nodes where an immune response is initiated. Injection of the immunomodulator OK-432 into the footpad skin caused a local increase in the number of Langerhans cells in the epidermis and led to an increased migration of dendritic cells to the lymph nodes. Under these conditions, a decrease in HSV-1 pathogenicity was noted. These observations indicate that the pathogenicity of herpes simplex virus type 1 in the skin is affected by Langerhans cell density and activity in the epidermis and the lymph nodes.

Role of Langerhans cells in epidermotropism of T cells

Certain T lymphocytes display a specific affinity for the epidermis (epidermotropism). Recent studies have suggested that Ia+ Langerhans cells (LCs) are possible targets for the epidermotropism. A variety of self-Ia-reactive cloned T cells were tested for their ability to migrate into the epidermis following intradermal inoculation into the footpads of syngeneic mice. Clone BB5 was chosen as representative of the epidermotropic T cells. We investigated whether the depletion of Ia+ LCs from the epidermis by tape-stripping could alter the migration of BB5 cells into the epidermis. The epidermal invasion of BB5 cells was markedly impaired in those mice whose LCs were depleted by 95% after repetitive tape-stripping. Because production of epidermal-derived thymocyte activating factor (ETAF) by the epidermal cells was augmented after repetitive tape-stripping, the diminished migration of BB5 cells into tape-stripped epidermis did not result from a decrease in ETAF production which is thought to attract T cells chemotactically. These results suggest that Ia+ LCs may play an inductive role in the preferential migration of T cells into the epidermis.

Immunopathologic study of lichenoid skin diseases: correlation between HLA-DR-positive keratinocytes or Langerhans cells and epidermotropic T cells

Skin biopsy specimens from 24 patients with different lichenoid skin diseases that had been proved histologically were studied immunohistologically. Marked differences were noted in the number of OKT6+/S100+ Langerhans cells within the epidermis and dermis in the lesional skin between lichen planus (and its related disease) and lupus erythematosus; in the former these cells were increased in number; in the latter they were decreased in number compared with those in uninvolved perilesional skin. Human lymphocyte antigen (HLA)-DR expression on keratinocytes was observed not only in lichenoid skin diseases but also in control cases without epidermal involvement. In the two cases of systemic lupus erythematosus, the uninvolved perilesional skin also show weak and focal HLA-DR reactivity in the basal layer. HLA-DR+ keratinocytes could play an important role at least in the perpetuation of epidermal cell damage mediated by T cells.