Enriched Langerhans cells express more HLA-DR determinants than blood-derived adherent cells (monocytes and dendritic cells)

The Langerhans cell: an underestimated cell in atopic disease

Langerhans cells (LC) are very potent antigen-presenting cells. In atopic disorders such as allergic rhinitis and atopic dermatitis LC are known to bear IgE surface molecules. IgE-positive LC can bind allergen and present it to T lymphocytes to induce an allergen-specific T-cell response and IgE synthesis. Therefore, IgE-bearing LC might play an important role in the triggering of the immune system to maintain ongoing IgE synthesis. The importance of the IgE-bearing LC in atopy has not been assessed but deserves further investigation to find out more about the part played by these cells, not only in the atopic disorders described here but also in others such as gastrointestinal allergy and allergic asthma.

Antigen presentation in patients with recrudescent orofacial herpes simplex virus infections

Recovery from epidermal herpes simplex virus (HSV) infection depends primarily on development of an effective cell-mediated immune response, possibly generated following antigen (Ag) presentation by epidermal cells (EC). The ability of EC to present HSV Ag was investigated in 12 subjects with occasional recrudescent facial HSV infections. All had circulating HSV specific antibodies and cell-mediated immunity to the virus. Peripheral blood mononuclear cell suspensions, depleted of antigen presenting cells (APC) by glass adherence and then enriched for T cells by adsorption on nylon wool columns, did not proliferate in response to HSV Ag. Both EC suspensions, prepared from suction blister roofs, and glass-adherent peripheral blood mononuclear cells (AC) preincubated with ultraviolet-inactivated HSV, reconstituted the T-cell proliferative response to HSV. EC were more efficient than AC at presenting HSV Ag to T cells. Depletion of CD1+ cells from EC suspensions by cell sorting reduced their ability to present HSV Ag and augmentation of CD1+ cell numbers supplemented it. Preincubation of EC or AC with monoclonal antibodies to major histocompatibility complex class II antigens DP, DQ or DR, blocked the lymphoproliferative response to HSV Ag. Evidence was obtained that cells co-ordinately expressing products of the DP, DQ and DR loci are involved in presentation of HSV Ag by both EC and AC.

Collaboration between human blood dendritic cells and monocytes in antigen presentation

We compared human blood dendritic cells and monocytes for their capacity to produce secreted and membrane interleukin 1 (IL-1), stimulate mixed leukocyte reaction (MLR) and augment microbial antigen-induced T lymphocyte proliferation. Our enriched dendritic cell and monocyte fractions contained greater than 80% and greater than 93% dendritic cells and monocytes, respectively. Monocytes produced about ten times higher amounts of membrane and secreted IL-1 than dendritic cells, which in turn were more potent in presenting HLA-DR antigens in MLR. Both accessory cell types presented purified protein derivative of tuberculin (PPD) equally well, whereas monocytes were better with fixed Bacillus Calmette Guérin (BCG) bacteria. Processing of BCG was chloroquine-sensitive. Coculture experiments suggested that there was collaboration or synergy between dendritic cells and monocytes in antigen processing and presentation.

Neopterin and alpha-interferon in patients affected by Kaposi's sarcoma from Africa

The presence of circulating alpha-interferon and neopterin was investigated in sera of 47 patients affected by African Kaposi's sarcoma, both HIV-seropositive (13 patients) and HIV-seronegative (34 patients). For comparison, analyses were also performed in 20 HIV-seropositive symptomatic African subjects as well as in 20 African and 20 Italian healthy individuals. Alpha-interferon and neopterin levels appeared significantly higher in comparison with healthy control groups (P less than 0.001) but not with HIV-seropositve African individuals without Kaposi's sarcoma. Moreover, alpha-interferon and neopterin levels were significantly higher in progressive Kaposi's sarcoma (27 patients) than in regressive Kaposi's sarcoma (20 patients) (P less than 0.001). A significant correlation between alpha-interferon and neopterin was observed (r = 0.57; P less than 0.01). Furthermore, alpha-interferon levels of HIV-seropositive Kaposi's sarcoma patients resulted significantly higher in comparison with the seronegative ones (P less than 0.05). It is concluded that alpha-interferon and neopterin may be reliable prognostic markers in Kaposi's sarcoma patients.

Human epidermal Langerhans cells and peripheral blood monocytes. Accessory cell function, autoactivating and alloactivating capacity and ETAF/IL-1 production

We compared the functional capacities of human epidermal Langerhans cells (LC) and peripheral blood monocytes. Epidermal sheets were obtained by a suction blister device. After enzymatic treatment LC were enriched by attaching them to IgG-located erythrocyte monolayers. On a per cell basis, LC were several times more efficient accessory cells than monocytes in augmenting nickel-and tuberculin (PPD)-induced T-cell proliferation. In mixed cell cultures LC stimulated both autologous and allogeneic T cells, whereas monocytes stimulated only allogeneic cells. In addition, LC were significantly more potent allogeneic stimulators than monocytes. Although monocytes were weaker accessory cells and allogeneic stimulators than LC, they induced higher interleukin 1 (IL-1) activities than LC-enriched or LC-depleted cells. These results indicate that there are functional differences between LC and monocytes and that antigen presentation and mediator secretion are not correlated.

Evaluation of in vitro predictive tests for irritation and allergic sensitization

Investigations of in vitro procedures to predict the potential of substances as skin irritants and as allergens inducing delayed hypersensitivity (contact dermatitis) are described, with indications of possible advances and known limitations. The examination of keratome slices of skin for release of enzymes, for changed histochemistry and for utilization of radioisotope-labelled amino acids will detect weak irritants but is of doubtful value for moderate irritants and will detect corrosive substances only through their inhibition of all cell activities. Fibroblast cultures, tested with Clostridium perfringens toxin and chemicals, show similar limitations in detecting moderate or severe irritants. Fibroblast cultures can be made more relevant to epidermal exposure by an overlying layer of agar containing keratin. In vitro tests to detect induction of sensitizing potential for delayed hypersensitivity have made little progress. The most promising approach is to treat antigen-presenting Langerhans cells with antigen and co-culture with lymphocytes. The lymphocytes may be examined for changes in receptor expression, for synthesis of interleukin 2, and possibly for responses to allergen if sufficient cells become specifically sensitized. There are several in vitro techniques to detect responses of in vivo- or in vitro-sensitized lymphocytes treated with antigen.