Peroxisome proliferator-activated receptor gamma activators affect the maturation of human monocyte-derived dendritic cells.

Peroxisome proliferator-activated receptor gamma (PPARgamma ), a member of the nuclear receptor superfamily, has recently been described as a modulator of macrophage functions and as an inhibitor of T cell proliferation. Here, we investigated the role of PPARgamma in dendritic cells (DC), the most potent antigen-presenting cells. We showed that PPARgamma is highly expressed in immature human monocyte-derived DC (MDDC) and that it may affect the immunostimulatory function of MDDC stimulated with lipopolysaccharide (LPS) or via CD40 ligand (CD40L). We found that the synthetic PPARgamma agonist rosiglitazone (as well as pioglitazone and troglitazone) significantly increases on LPS- and CD40L-activated MDDC, the surface expression of CD36 (by 184% and 104%, respectively) and CD86 (by 54% and 48%), whereas it reduces the synthesis of CD80 (by 42% and 42%). Moreover, activation of PPARgamma resulted in a dramatic decreased secretion of the Th1-promoting factor IL-12 in LPS- and CD40L-stimulated cells (by 47% and 62%), while the production of IL-1beta, TNF-alpha, IL-6 and IL-10 was unaffected. Finally, PPARgamma ligands down-modulate the synthesis of IFN-gamma -inducible protein-10 (recently termed as CXCL10) and RANTES (CCL5), both chemokines involved in the recruitment of Th1 lymphocytes (by 49% and 30%), but not the levels of the Th2 cell-attracting chemokines,macrophage-derived chemokine (CCL22) and thymus and activation regulated chemokine (CCL17), in mature MDDC. Taken together, our data suggest that activation of PPARgamma in human DC may have an impact in the orientation of primary and secondary immune responses by favoring type 2 responses.

Th2 polarization by Der p 1--pulsed monocyte-derived dendritic cells is due to the allergic status of the donors.

The polarization of the immune response toward a Th2 or a Th1 profile can be mediated by dendritic cells (DCs) following antigen presentation and interaction with T cells. Costimulatory molecules such as CD80 and CD86 expressed by DCs, the polarizing cytokine environment during DC--T-cell interaction, and also the nature of the antigen are critical in the orientation of the immune response. In this study, the effect of the cysteine protease Der p 1, one of the major allergens of the house dust mite Dermatophagoides pteronyssinus, on these different parameters was evaluated comparatively on monocyte-derived DCs obtained from healthy donors, from pollen-sensitive patients, or from patients sensitive to Dermatophagoides pteronyssinus. Results showed that Der p 1 induced an increase in CD86 expression only on DCs from house dust mite--sensitive patients. This was also associated with a higher capacity to induce T-cell proliferation, a rapid increase in the production of proinflammatory cytokines, tumor necrosis factor--alpha and interleukin (IL)-1 beta, and the type 2 cytokine IL-10. No changes in the release of IL-12 p70 were induced by Der p 1. Finally, purified T cells from house dust mite-sensitive patients stimulated by autologous Der p 1--pulsed DCs preferentially produced IL-4 rather than interferon-gamma. These effects were abolished in the presence of the inactive precursor of Der p 1 (ProDer p 1). Taken together, these data suggest that DCs from house dust mite--sensitive patients, in contrast to DCs from healthy donors and from pollen-sensitive patients, exposed to Der p 1 play a pivotal role in the enhancement of the Th2 response associated with the allergic reaction developed in response to house dust mite exposure. (Blood. 2001;98:1135-1141)

Modulation of high-affinity IgE receptor expression in blood monocytes: opposite effect of IL-4 and glucocorticoids.

BACKGROUND: The expression of high-affinity IgE receptor (Fc epsilon RI) is increased in blood monocytes (BMs) from allergic patients compared with those of nonatopic subjects (NASs). OBJECTIVE: We investigated the in vitro effect of cytokines involved in allergic diseases on the modulation of Fc epsilon RI expression in BMs from allergic asthmatic patients (AAPs) and NASs. The influence of in vitro and in vivo treatments with glucocorticoids (GCs) was also assessed. METHODS: Fc epsilon RI alpha-chain expression on BMs evaluated by flow cytometry analysis was studied ex vivo in AAPs treated or not with GCs and in NASs. IgE receptor expression was also evaluated in vitro with or without stimulation by IL-4, IL-13, GM-CSF, and/or GCs. Messenger (m)RNA expression was also analyzed with RT-PCR. RESULTS: The expression of the Fc epsilon RI alpha chain was significantly increased in BMs from untreated patients, with AAPs compared with NASs (P <.05). In steroid-treated AAPs Fc epsilon RI alpha-chain expression returned to the level found in BMs from NASs. In vitro addition of IL-4 induced a dose-dependent increase in Fc epsilon RI alpha-chain expression on BMs from NASs, and this effect was significantly enhanced with BMs from AAPs. Fc epsilon RI alpha-chain mRNA was significantly upregulated by IL-4, whereas the beta chain was always undetectable. The gamma chain was not modulated by IL-4. Similar findings were obtained with IL-13. In contrast with CD23 expression, GM-CSF alone or in coincubation with IL-4 had no effect on Fc epsilon RI alpha-chain expression in BMs. Lastly, GCs significantly inhibited in vitro the IL-4-induced Fc epsilon RI alpha-chain expression (P <.05). CONCLUSION: Two different pathways by which Fc epsilon RI alpha-chain expression was modulated in BMs were identified: (1) the enhancing effect of IL-4 and IL-13 and (2) the inhibitory effect of GCs. Modulation of Fc epsilon RI alpha-chain expression on BMs may affect their capacity to regulate allergic inflammation.

Macrophage inflammatory protein 3alpha is involved in the constitutive trafficking of epidermal langerhans cells.

Certain types of dendritic cells (DCs) appear in inflammatory lesions of various etiologies, whereas other DCs, e.g., Langerhans cells (LCs), populate peripheral organs constitutively. Until now, the molecular mechanism behind such differential behavior has not been elucidated. Here, we show that CD1a(+) LC precursors respond selectively and specifically to the CC chemokine macrophage inflammatory protein (MIP)-3alpha. In contrast, CD14(+) precursors of DC and monocytes are not attracted by MIP-3alpha. LCs lose the migratory responsiveness to MIP-3alpha during their maturation, and non-LC DCs do not acquire MIP-3alpha sensitivity. The notion that MIP-3alpha may be responsible for selective LC recruitment into the epidermis is further supported by the following observations: (a) MIP-3alpha is expressed by keratinocytes and venular endothelial cells in clinically normal appearing human skin; (b) LCs express CC chemokine receptor (CCR)6, the sole MIP-3alpha receptor both in situ and in vitro; and (c) non-LC DCs that are not found in normal epidermis lack CCR6. The mature forms of LCs and non-LC DCs display comparable sensitivity for MIP-3beta, a CCR7 ligand, suggesting that DC subtype-specific chemokine responses are restricted to the committed precursor stage. Although LC precursors express primarily CCR6, non-LC DC precursors display a broad chemokine receptor repertoire. These findings reflect a scenario where the differential expression of chemokine receptors by two different subpopulations of DCs determines their functional behavior. One type, the LC, responds to MIP-3alpha and enters skin to screen the epidermis constitutively, whereas the other type, the "inflammatory" DC, migrates in response to a wide array of different chemokines and is involved in the amplification and modulation of the inflammatory tissue response.

CD34+ cell-derived CD14+ precursor cells develop into Langerhans cells in a TGF-beta 1-dependent manner.

Langerhans cells (LC) are CD1a+E-cadherin (E-cad)+Birbeck granule+ but CD11b-CD36-factor XIIIa (FXIIIa)- members of the dendritic cell (DC) family. Evidence holds that LC originate from CD1a+CD14- rather than CD14+CD1a- progenitors, both of which arise from GM-CSF/TNF-alpha-stimulated CD34+ stem cells. The CD14+CD1a- progenitors, on the other hand, can give rise to a separate DC type characterized by its CD1a+CD11b+CD36+FXIIIa+E-cad-BG- phenotype (non-LC DC). Although GM-CSF/TNF-alpha are important for both LC and non-LC DC differentiation, TGF-beta 1 is thought to preferentially promote LC development in vitro and in vivo. However, the hemopoietic biology of this process and the nature of TGF-beta 1-responsive LC precursors (LCp) are not well understood. Here we show that CD14+ precursors in the presence, but not in the absence, of TGF-beta 1 give rise to a progeny that fulfills all major criteria of LC. In contrast, LC development from CD1a+ progenitors was TGF-beta 1 independent. Further studies revealed that CD14+ precursors contain a CD11b+ and a CD11b- subpopulation. When either subset was stimulated with GM-CSF/TNF-alpha and TGF-beta 1, only CD14+CD11b- cells differentiated into LC. The CD11b+ cells, on the other hand, acquired non-LC DC features only. The higher doubling rates of cells entering the CD14+ LCp rather than the CD1a+ LCp pathway add to the importance of TGF-beta 1 for LC development. Because CD14+CD11b- precursors are multipotent cells that can enter LC or macrophage differentiation, it is suggested that these cells, if present at the tissue level, endow a given organ with the property to generate diverse cell types in response to the local cytokine milieu.

In vitro HIV1 infection of CD34+ progenitor-derived dendritic/Langerhans cells at different stages of their differentiation in the presence of GM-CSF/TNF alpha.

Langerhans cells (LC) are antigen-presenting cells which are found in areas at risk of inoculation by the human immunodeficiency virus (HIV). LC were shown to be sensitive to in vitro infection by HIV1. They could be generated in vitro by culturing CD34+ haematopoietic progenitors with GM-CSF+TNF alpha. In this study, we tested the sensitivity to HIV1 infection of in vitro generated LC throughout their differentiation and we investigated the effect of such an infection on in vitro differentiation. Phenotypic controls were performed using FACS analysis on day 6 for the presence of a CD1a+ cell population, and differentiation was assessed by transmission electron microscopy on day 13 for the presence of Birbeck granules. CD34+ cells were purified from cord blood mononuclear cells by magnetic separation. Cell suspensions were infected with either a T-lymphotropic, syncytium-inducing isolate (HXB2) or a macrophage-tropic, non-syncytium-inducing isolate (Ba-L). Viral particle release was measured by p24 antigen production in the culture supernatant. A high level of p24 production was noted on day 13 of postinfection only when infection was carried out with Ba-L isolate on cells generated after 6 days in culture with GM/CSF+TNF alpha. No infection of CD34+ progenitor cells was obtained either with Ba-L isolate or HXB2. The sensitivity of Langerhans cell/dendritic cell (LC/DC) precursors to NSI isolate (Ba-L) seemed to coincide with the early stage of differentiation (CD1a antigen appearance). The infection did not alter the differentiation of in vitro generated LC, which presented their specific ultrastructural marker of epidermal environment, i.e. Birbeck granules from day 15 of the culture as compared to control culture. These results highlight the HIV infectibility of a differentiated population of LC/DC generated in vitro from CD34+ progenitors.

[Epithelial dendritic cells and HIV-1 infection in vivo and in vitro]. / Cellules dendritiques épithéliales et infection par HIV-1 in vivo et in vitro.

The skin and mucosa are the first line of defense of the organism against external agents, not only as a barrier between the body and the environment but also as the site of initiation of immune reactions. The immunocompetent epidermal cells which act as antigen-presenting cells (APC) are Langerhans cells (LC). Many indirect and/or direct experimental data have shown that LC may be a privileged target, reservoir and vector of dissemination for the human immunodeficiency virus (HIV) from the inoculation sites (mucosa?) to lymph nodes where the emigrated infected LC could infect T lymphocytes. In vitro infection confirms their permissivity to viral replication. HIV infection may modify the APC function of LC which could contribute to amplify the immunosuppressive state found in AIDS. Furthermore, mechanisms leading to the re-activation of viral expression at the cutaneous level need to be explored. An ideal animal model may readily clarify the role of LC in AIDS pathology and in transmucosal infection.

Detection of HIV-specific DNA sequences in epidermal Langerhans cells infected in vitro by means of a cell-free system.

As dendritic antigen-presenting cells in skin and mucous membranes, Langerhans cells (LC) are found in areas at risk of inoculation by the human immunodeficiency virus (HIV). LC have been reported as targets for HIV-1. The aim of the present study was to investigate whether LC can be experimentally infected by HIV provided by a cell-free infection system. A cell-free suspensions was prepared from viral particles provided by chronically infected cell lines (U937 or H9 cells) by low-speed centrifugation followed by 0.45-microns filtration. LC-enriched epidermal cell (EC) suspensions with no CD3+ cells (assessed by flow cytometry and electron microscopy) and uninfected U937 cells (cell-free infection system control) were infected with two isolates (HTL VIII-B and RF). The infectiousness of the cell-free virus fluids was controlled on U937 cells where proviral DNA was amplified (gag, pol, and env gene sequences by the polymerase chain reaction, PCR) and release of virus particles into the supernatant was controlled either by measure of the reverse transcriptase (RT) activity or detection of viral RNA amplified by RT-PCR for the gag gene sequences). Proviral DNA (gag gene sequences) was found in LC-enriched epidermal cellular DNA from day 4 post-infection with isolate HTL VIII-B and from day 7 with isolate RF. Although the RT activity did not reach a significantly high level, viral RNA was found in the supernatant of LC-enriched EC cultures at the same time as proviral DNA was detected in LC.(ABSTRACT TRUNCATED AT 250 WORDS)