Cutting edge: virus selectively primes human langerhans cells for CD70 expression promoting CD8+ T cell responses.

The two outermost compartments of skin are populated by different Ag-presenting dendritic cell types. Epidermal Langerhans cells (LCs) are evolutionarily adapted to the continuous presence of harmless skin commensals by the selective lack of cell surface TLRs that sense bacteria. In this article, we analyze the ability of LCs and dermal dendritic cells (DDCs) to respond to virus infection. Live virus and intracellular TLR3-agonist dsRNA commit LCs more effectively than DDCs to stimulate naive CD8(+) T cell expansion and their differentiation into effector cells. This potent CD8(+) T cell-promoting capacity of LCs is causally related to high levels of virus-induced CD70 expression but not to IL-12 production. These data suggest a remarkable specialization of LCs in the induction of pathogen class-specific adaptive immunity. Whereas LCs ignore bacteria, they are superior to DDCs to initiate effective CD70-mediated CD8(+) T cells in response to virus stimulation.

Expression profiles of ProEx C and Ki67 in squamous cell carcinoma in situ of the skin and their relationship with human papillomavirus genotypes.

BACKGROUND: ProExC is a new marker for identification of precursor lesions of cervical carcinoma. Its utility in noncervical squamous cell carcinoma in situ (SCCIS) such as Bowen's disease (BD) and actinic keratosis (AK) where human papillomavirus (HPV) plays a role has not been elucidated. Our aim was to ascertain the immunohistochemical features and clinical utility of ProExC in SCCIS of the skin. METHODS: HPV presence was tested in SCCIS (38 BD and 7 AK) using GP5+/6+ and Short PCR fragment (SPF) primers and subsequently genotyped. Histopathologic sections were stained for ProExC and Ki67. A set of non-neoplastic skin proliferative lesions were included for immunohistochemical evaluation [14 psoriasis (PS) and 6 psoriasiform dermatitis (PSD)]. RESULTS: HPV was detected in 18.9% BD. ProExC and Ki67 in the whole epidermis thickness was observed in 86.5 and 37.1% BD, respectively (p < 0.0001). ProExC and Ki67 were restricted to the lower third of the epidermis in PS and PSD. CONCLUSIONS: ProExC expression is not associated with HPV in SCCIS of the skin. Proliferating cells are better delineated in SCCIS by ProExC which may be useful to assess the extent of these lesions. Different immunohistochemical profiles seen in neoplasic and non-neoplastic skin lesions suggest diverse alteration of cell-cycle kinetics.

Glycan modification of the tumor antigen gp100 targets DC-SIGN to enhance dendritic cell induced antigen presentation to T cells.

Dendritic cells (DC) have gained much interest in the field of anticancer vaccine development because of their central function in immune regulation. However, the clinical application of ex vivo cultured DC has significant disadvantages. A vaccine that targets dendritic cells in vivo and enhances antigen presentation would be of great benefit. Because of its DC-restricted expression pattern, and its function as an antigen uptake receptor, DC-SIGN is an interesting candidate target structure for human immature DC. Here, we studied whether modification of the melanoma differentiation antigen gp100 with DC-SIGN-interacting glycans enhances targeting to human DC. A high-mannose form of gp100, as protein or as tumor lysate, not only interacted specifically with DC through DC-SIGN but also resulted in an enhanced antigen presentation to gp100-specific CD4(+) T cells. Our results indicate that glycan modification of tumor antigens to target C-type lectin receptors, such as DC-SIGN, is a new way to develop in vivo targeting DC strategies that simultaneously enhance the induction of tumor-specific T cells.

Schistosoma mansoni soluble egg antigens are internalized by human dendritic cells through multiple C-type lectins and suppress TLR-induced dendritic cell activation.

In schistosomiasis, a parasitic disease caused by helminths, the parasite eggs induce a T helper 2 cell (T(H)2) response in the host. Here, the specific role of human monocyte-derived dendritic cells (DCs) in initiation and polarization of the egg-specific T cell responses was examined. We demonstrate that immature DCs (iDCs) pulsed with schistosome soluble egg antigens (SEA) do not show an increase in expression of co-stimulatory molecules or cytokines, indicating that no conventional maturation was induced. The ability of SEA to affect the Toll-like receptor (TLR) induced maturation of iDCs was examined by copulsing the DCs with SEA and TLR-ligands. SEA suppressed both the maturation of iDCs induced by poly-I:C and LPS, as indicated by a decrease in co-stimulatory molecule expression and production of IL-12, IL-6 and TNF-alpha. In addition, SEA suppressed T(H)1 responses induced by the poly-I:C-pulsed DCs, and skewed the LPS-induced mixed response towards a T(H)2 response. Immature DCs rapidly internalized SEA through the C-type lectins DC-SIGN, MGL and the mannose receptor and the antigens were targeted to MHC class II-positive lysosomal compartments. The internalization of SEA by multiple C-type lectins may be important to regulate the response of the iDCs to TLR-induced signals.

Neutrophils mediate immune modulation of dendritic cells through glycosylation-dependent interactions between Mac-1 and DC-SIGN.

Neutrophils are key players of the innate immune system that provide a first line of defense against invading pathogens. However, it is unknown whether neutrophils can interact with dendritic cells (DCs) to modulate adaptive immune responses. We demonstrate that neutrophils strongly cluster with immature DCs and that activated, not resting, neutrophils induce maturation of DCs that enables these DCs to trigger strong T cell proliferation and T helper type 1 polarization of T cells. This neutrophil-DC interaction is driven by the binding of the DC-specific, C-type lectin DC-SIGN to the beta(2)-integrin Mac-1. Strikingly, DC-SIGN only interacts with Mac-1 from neutrophils, but not from other leukocytes, mainly because of specific Lewis(x) carbohydrates that are present on the alpha(M) chain of Mac-1 from neutrophils. Furthermore, we show that besides the formation of cellular contact, the tumor necrosis factor-alpha produced by activated neutrophils is essential for inducing DC maturation. Our data demonstrate that DC-SIGN and Mac-1 define a molecular pathway to establish cellular adhesion between DCs and neutrophils, thereby providing a novel cellular link between innate and adaptive immunity.

Lactoferrin prevents dendritic cell-mediated human immunodeficiency virus type 1 transmission by blocking the DC-SIGN--gp120 interaction.

One of the cell types first encountered by human immunodeficiency virus type 1 (HIV-1) following sexual transmission are dendritic cells (DC). DC capture HIV-1 through C-type lectin receptors, of which the best studied example is DC-SIGN, which mediates HIV-1 internalization. DC can keep the virus infectious for several days and are able to transmit HIV-1 to CD4(+) T cells. We tested proteins from milk and serum for their ability to block DC-mediated HIV-1 transmission, of which bovine lactoferrin (bLF) is the most potent inhibitor. bLF binds strongly to DC-SIGN, thus preventing virus capture and subsequent transmission. Interestingly, bLF is a much more efficient inhibitor of transmission than human lactoferrin. Since bLF is nontoxic and easy to purify in large quantities, it is an interesting candidate microbicide against HIV-1. Another advantage of bLF is its ability to block HIV-1 replication in T cells. DC-mediated capture of a bLF-resistant HIV-1 variant that was selected during long-term culturing in T cells could still be blocked by bLF. This underscores the usefulness of bLF as a microbicide drug to prevent HIV-1 transmission.

Mycobacteria target DC-SIGN to suppress dendritic cell function.

Mycobacterium tuberculosis represents a world-wide health risk and immunosuppression is a particular problem in M. tuberculosis infections. Although macrophages are primarily infected, dendritic cells (DCs) are important in inducing cellular immune responses against M. tuberculosis. We hypothesized that DCs represent a target for M. tuberculosis and that the observed immuno-suppression results from modulation of DC functions. We demonstrate that the DC-specific C-type lectin DC-SIGN is an important receptor on DCs that captures and internalizes intact Mycobacterium bovis bacillus Calmette-Guérin (BCG) through the mycobacterial cell wall component ManLAM. Antibodies against DC-SIGN block M. bovis BCG infection of DCs. ManLAM is also secreted by M. tuberculosis-infected macrophages and has been implicated as a virulence factor. Strikingly, ManLAM binding to DC-SIGN prevents mycobacteria- or LPS-induced DC maturation. Both mycobacteria and LPS induce DC maturation through Toll-like receptor (TLR) signaling, suggesting that DC-SIGN, upon binding of ManLAM, interferes with TLR-mediated signals. Blocking antibodies against DC-SIGN reverse the ManLAM-mediated immunosuppressive effects. Our results suggest that M. tuberculosis targets DC-SIGN both to infect DCs and to down-regulate DC-mediated immune responses. Moreover, we demonstrate that DC-SIGN has a broader pathogen recognition profile than previously shown, suggesting that DC-SIGN may represent a molecular target for clinical intervention in infections other than HIV-1.