Langerhans cell presentation of sheep red blood cells induces antibody production

Down-regulation of an established immune response via chemical carcinogen or UVB-altered skin

The ability to produce antigen-specific down-regulation of an established immune response was investigated in 2,4,6-trinitrochlorobenzene (TNCB)-immune mice by delivery of antigen through chemical carcinogen- or ultraviolet B (UVB)-treated skin. When TNCB-immune mice were treated on the dorsal trunk skin with 7,12-dimethylbenz(a)anthracene (DMBA) followed by TNCB there was an antigen-specific reduction in both contact sensitivity and antibody production. Further, immune mice that received spleen cells from naive syngeneic donors treated with DMBA followed by TNCB also exhibited a reduction in both contact sensitivity and antibody production. In contrast, mice treated with UVB irradiation followed by TNCB had a reduction in contact sensitivity but not antibody production. These results provide evidence that an ongoing immune response can be manipulated by immunization through a modified skin immune system. This may provide a beneficial approach for the treatment of autoimmune disease.

The migration of Langerhans' cells into and out of lymph nodes draining normal, carcinogen and antigen-treated sheep skin

Epidermal Langerhans' cell (LC) migration to the regional lymph node and beyond into central lymph was examined in sheep following topical application of the complete chemical carcinogen 7,12-dimethylbenz(a)anthracene (DMBA) or the contact sensitizing antigen 2,4,6-trinitrochlorobenzene (TNCB). This was facilitated by cannulating previously constructed pseudoafferent lymphatic vessels draining the skin treated with these agents or alternatively, the efferent lymphatic vessel of the regional lymph node. Application of DMBA resulted in a biphasic increase in LC migration. There was an initial increase in LC migration at 25 h with the maximum response (3.6 x 10(7) LC/h) occurring approximately 5 days after DMBA treatment. In contrast, the contact sensitizing antigen TNCB caused enhanced LC migration within minutes of the application of antigen (3.3 x 10(6) LC/h) and peak migration at 8-12 h. Examination of efferent lymph cells from the regional lymph node after DMBA treatment showed uncharacteristically large numbers of LC traversing the lymph node. These LC migration patterns suggest different mechanisms may trigger the migration of LC from skin after the application of DMBA to those associated with the normal processes of antigen presentation.

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.

Langerhans cell depletion in gliotoxin-treated murine epidermis

Langerhans cells (LC) are dendritic antigen presenting cells of bone marrow origin which reside in the suprabasal layer of the epidermis. They express high concentrations of Class II MHC glycoproteins on their plasma membrane and transport cutaneous antigen to local lymph nodes for presentation to helper T cells. They are thus essential for the induction of cutaneous immunity. Gliotoxin is a member of the epipolythiodioxopiperazine (ETP) group of fungal metabolites, derived from the human pathogen Aspergillus fumigatus. It has been shown to have immunomodulating properties in vivo and in vitro, and has been proposed as a potential immunosuppressant for transplantation therapy. Epicutaneous application of gliotoxin reduced the numbers of epidermal LC by 30-35 per cent with an associated morphological change from highly dendritic to a more rounded form. Electron microscopic studies showed selective damage to LC at very low (nM) concentrations of gliotoxin, with no obvious effect on adjacent keratinocytes. LC numbers remained depleted for 13 weeks after initial treatment, suggesting that systemic suppression or prolonged retention of gliotoxin within the skin may play a role in its mechanism of action.

Immunophenotypic and cell cycle analysis of lymph node cells from dimethylbenzanthracene-treated mice

The chemical carcinogen 7, 12-dimethylbenz-(a)anthracene (DMBA) depletes Langerhans cells from murine epidermis. Application of contact sensitizers to DMBA-treated skin induces specific immunological tolerance due to a DMBA-resistant epidermal antigen presenting cell (APC) migrating to local lymph nodes where it presents antigen in a way which activates suppressor cells. As alterations in local lymph node lymphocytes may enhance the ability of the DMBA-resistant APC to activate suppressor cells, these cells were examined in DMBA-treated mice. Lymph nodes in DMBA-treated mice had normal morphology but were larger and contained increased numbers of lymphocytes. Cell cycle analysis revealed that these lymphocytes did not arise from division within the lymph node, suggesting alterations in homing properties of lymphocytes. Contact sensitizer applied to DMBA-treated skin did not increase lymphocyte division, possibly due to suppressor cell inhibition of the development of effector lymphocytes. DMBA treatment had no effect on B cells or Ia expression, but decreased levels of the T lymphocyte cell surface molecule Thy-1, and increased L3T4 and Lyt-2 as quantitated by flow cytofluorimetry. These changes could influence the development of immune responses as these T cell molecules are receptors involved in lymphocyte interactions.

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.

Suppressor cell activation and enhanced skin allograft survival after tumor promotor but not initiator induced depletion of cutaneous Langerhans cells

During chemical carcinogenesis Langerhans cells (LC) are depleted from the epidermis, disrupting the normal immunological functions of the skin. Tumor promotors but not initiators, have been shown to deplete adenosine triphosphatase (ATPase)-positive LC from the skin and therefore the cutaneous immune system may be impaired during tumor promotion but not initiation. The present study shows that the tumor promotor 12-O-tetradecanoylphorbol 13-acetate (TPA) but not the initiator urethane depletes Ia-positive LC from BALB/c murine ear epidermis, and beta-glucuronidase-positive LC from C57BL mouse tail skin. Sensitization with 2,4-dinitrofluorobenzene (DNFB) through urethane-treated skin resulted in a normal contact sensitivity response when the mice were challenged 5 days later. In contrast, tolerance resulted from sensitization through TPA-treated skin as a result of the generation of suppressor cells. In addition, TPA but not urethane-treated C57BL mouse tail skin survived for an extended time when grafted onto histoincompatible BALB/c mice. Therefore, impairment of the normal immunological functions of skin resulted from treatment with the tumor promotor TPA but not the tumor initiator urethane, which suggests that a loss of LC during tumor promotion may impair immunological protection against skin tumors.

Sensitization through carcinogen-induced Langerhans cell-deficient skin activates specific long-lived suppressor cells for both cellular and humoral immunity

Application of 2,4-dinitrofluorobenzene (DNFB) to BALB/c mouse skin depleted of epidermal Langerhans cells (LC) by the chemical carcinogen 7,12-dimethylbenz[a]anthracene (DMBA) activated cells which suppress both contact sensitivity and antibody production when transferred into naive host mice. Tolerance was induced by a concentration of DNFB optimal for inducing contact sensitivity in solvent-treated control mice. The cellular and humoral responses of hosts to a second antigen, 2,4,6-trinitrochlorobenzene (TNCB), were unaffected by these suppressor cells, demonstrating specificity for DNFB. Suppressor cells for cellular and humoral immunity could still be demonstrated 6 months following activation, by which time some mice had died, presumably of old age. The dose responses to sensitizer for generation of cells which suppressed contact sensitivity and antibody production differed, indicating that separate populations of suppressor cells probably inhibit these responses. Hence, during cutaneous chemical carcinogenesis, depletion of LC may allow activation of specific long-lived suppressor cells capable of inhibiting cellular or humoral antitumor immune responses.