SummaryHuman plasmacytoid dendritic cells (PDC) are crucial for innate and adaptive immune responses against viral infections, mainly through production of type I interferons. Evidence is accumulating that PDC surface receptors play an important role in this process. To investigate the PDC phenotype in more detail, a chip-based expression analysis of surface receptors was combined with respective flow cytometry data obtained from fresh PDC, PDC exposed to interleukin-3 (IL-3) and/or herpes simplex virus type 1 (HSV-1). CD156b, CD229, CD305 and CD319 were newly identified on the surface of PDC, and CD180 was identified as a new intracellular antigen. After correction for multiple comparisons, a total of 33 receptors were found to be significantly regulated upon exposure to IL-3, HSV-1 or IL-3 and HSV-1. These were receptors involved in chemotaxis, antigen uptake, activation and maturation, migration, apoptosis, cytotoxicity and costimulation. Infectious and ultraviolet-inactivated HSV-1 did not differentially affect surface receptor regulation, consistent with the lack of productive virus infection in PDC, which was confirmed by HSV-1 real-time polymerase chain reaction and experiments involving autofluorescing HSV-1 particles. Viral entry was mediated at least in part by endocytosis. Time-course experiments provided evidence of a co-ordinated regulation of PDC surface markers, which play a specific role in different aspects of PDC function such as attraction to inflamed tissue, antigen recognition and subsequent migration to secondary lymphatic tissue. This knowledge can be used to investigate PDC surface receptor functions in interactions with other cells of the innate and adaptive immune system, particularly natural killer cells and cytotoxic T lymphocytes.

Plasmacytoid dendritic cells (PDC), the main producers of type I IFNs in the blood, are important for the recognition and control of viral and bacterial infections. Because several viruses induce IFN-α production, severe courses of herpes virus infections in nonimmunocompromised patients may be related to numerical or functional PDC deficits. To evaluate this hypothesis, PBMC and PDC were repeatedly isolated from nine patients with acute retinal necrosis (ARN), caused by herpes simplex or varicella zoster virus. The patients experienced meningitis/encephalitis and frequent infections in childhood (n = 2), recurrent herpes virus infections at unusual localizations (n = 2), ocular surgery (n = 1), infections (n = 4), and stress around ARN (n = 6). The median percentage of isolated PDC was significantly lower in patients compared with 18 age-matched healthy controls (p < 0.001), confirmed by FACS analysis using peripheral blood, and was extremely low during acute disease. PDC counts dropped in five controls suffering from respiratory infections or diarrhea. IFN-α production in PDC and PBMC exposed to different stimuli was significantly lower in patients than in controls (p < 0.05). Anergy to these stimuli was observed on four occasions, in particular during acute disease. PDC of patients showed up-regulated IFN regulatory factor-7 mRNA levels and evidence of in vivo activation (CD80) and maturation (CD83) (p < 0.05). CD8+ cell responses were significantly lower in patients vs controls (p = 0.04). These data support a risk factor model in which numerical and functional deficits in PDC-mediated innate immune responses contribute to an impaired control of latent herpes virus infections and subsequent development of ARN.

Chronic immune activation, triggered by plasmacytoid dendritic cell (PDC) interferon (IFN)-alpha production, plays an important role in HIV-1 pathogenesis. As the entry of HIV-1 seems to be important for the activation of PDC, we directly characterized the viral entry into these cells using immuno-electron microscopy, cellular fractionation, confocal imaging, and functional experiments. After attachment to PDC, viruses were taken up in an energy-dependent manner. The virions were located in compartments positive for caveolin; early endosomal antigen 1; Rab GTPases 5, 7 and 9; lysosomal-associated membrane protein 1. PDC harbored more virus in endocytic vesicles than CD4+ T cells (p<0.05). Blocking CD4 inhibited the uptake of virions into cytosolic and endosomal compartments. Dynasore, an inhibitor of dynamin-dependent endocytosis, not the fusion inhibitor T-20, reduced the HIV-1 induced IFN-alpha production. Altogether, our morphological and functional data support the role of endocytosis for the entry and IFN-alpha induction of HIV-1 in PDC.

Plasmacytoid dendritic cells (PDC) are major producers of type I interferons (IFN) in response to human immunodeficiency virus type 1 (HIV-1) infection. To better define the underlying mechanisms, we studied the magnitude of alpha IFN (IFN-␣) induction by recombinant viruses containing changes in the Env protein that impair or disrupt CD4 binding or expressing primary env alleles with differential coreceptor tropism. We found that the CD4 binding affinity but not the viral coreceptor usage is critical for the attachment of autofluorescing HIV-1 to PDC and for subsequent IFN-␣ induction. Our results illustrate the importance of the gp120-CD4 interaction in determining HIV-1-induced immune stimulation via IFN-␣ production.

No abstract