Lorant Farkas

Plasmacytoid Dendritic Cells (Natural Interferon- α/β-Producing Cells) Accumulate in Cutaneous Lupus Erythematosus Lesions

Plasmacytoid dendritic cell (P-DC) precursors in peripheral blood produce large amounts of interferon (IFN)-alpha/beta when triggered by viruses. However, when incubated with interleukin-3 and CD40 ligand, the same precursors differentiate into mature DCs that stimulate naïve CD4(+) T cells to produce Th2 cytokines. We recently reported that P-DCs accumulate in nasal mucosa of experimentally induced allergic rhinitis, supporting a role for this DC subset in Th2-dominated inflammation. Here we examined whether P-DCs accumulate in cutaneous lesions of lupus erythematosus (LE), a disorder associated with increased IFN-alpha/beta production. Our results showed that P-DCs were present in 14 out of 15 tissue specimens of cutaneous LE lesions, but not in normal skin. Importantly, the density of P-DCs in affected skin correlated well (r(s) = 0.79,P < 0.0005) with the high number of cells expressing the IFN-alpha/beta-inducible protein MxA, suggesting that P-DCs produce IFN-alpha/beta locally. Accumulation of P-DCs coincided also with the expression of L-selectin ligand peripheral lymph node addressin on dermal vascular endothelium, adding further support to the notion that these adhesion molecules are important in P-DC extravasation to peripheral tissue sites. Together, our findings suggested that P-DCs are an important source of IFN-alpha/beta in cutaneous LE lesions and may therefore be of pathogenic importance.

Regular ArticlesPlasmacytoid Dendritic Cells (Natural Interferon- α/β-Producing Cells) Accumulate in Cutaneous Lupus Erythematosus Lesions

Plasmacytoid dendritic cell (P-DC) precursors in peripheral blood produce large amounts of interferon (IFN)-alpha/beta when triggered by viruses. However, when incubated with interleukin-3 and CD40 ligand, the same precursors differentiate into mature DCs that stimulate naïve CD4(+) T cells to produce Th2 cytokines. We recently reported that P-DCs accumulate in nasal mucosa of experimentally induced allergic rhinitis, supporting a role for this DC subset in Th2-dominated inflammation. Here we examined whether P-DCs accumulate in cutaneous lesions of lupus erythematosus (LE), a disorder associated with increased IFN-alpha/beta production. Our results showed that P-DCs were present in 14 out of 15 tissue specimens of cutaneous LE lesions, but not in normal skin. Importantly, the density of P-DCs in affected skin correlated well (r(s) = 0.79,P < 0.0005) with the high number of cells expressing the IFN-alpha/beta-inducible protein MxA, suggesting that P-DCs produce IFN-alpha/beta locally. Accumulation of P-DCs coincided also with the expression of L-selectin ligand peripheral lymph node addressin on dermal vascular endothelium, adding further support to the notion that these adhesion molecules are important in P-DC extravasation to peripheral tissue sites. Together, our findings suggested that P-DCs are an important source of IFN-alpha/beta in cutaneous LE lesions and may therefore be of pathogenic importance.

Experimentally Induced Recruitment of Plasmacytoid (CD123high) Dendritic Cells in Human Nasal Allergy

Recent evidence suggests that the previously enigmatic cell type designated plasmacytoid monocytes can function as dendritic cells and contribute substantially to both innate and adaptive immunity. This cell type has previously been described only in bone marrow, blood, and organized lymphoid tissue, but not at effector sites with direct Ag exposure such as the mucosae. Plasmacytoid dendritic cells (P-DCs) matured in vitro can induce T cells to produce allergy-promoting Th2 cytokines; therefore, their possible occurrence in nasal mucosa during experimentally elicited allergic rhinitis was examined. Patients with silent nasal allergy were challenged topically with relevant allergen daily for 7 days. Biopsy specimens as well as blood samples were obtained before and during such provocation, and P-DCs were identified by their high expression of CD123 (IL-3R α-chain), together with CD45RA. Our results showed that P-DCs were present in low and variable numbers in normal nasal mucosa but increased dramatically during the allergic reaction. This accumulation concurred with the expression of the L-selectin ligand peripheral lymph node addressin on the mucosal vascular endothelium. The latter observation was particularly interesting in view of the high levels of L-selectin on circulating P-DC precursors and of previous reports suggesting that these cells can enter organized lymphoid tissue via high endothelial venules (which express peripheral lymph node addressin constitutively). Together, our findings suggested that P-DCs are involved in the triggering of airway allergy and that they are directed to allergic lesions by adhesion molecules that normally mediate leukocyte extravasation in organized lymphoid tissue.

Involvement of plasmacytoid dendritic cells in human diseases.

In vitro studies have reported that plasmacytoid dendritic cells (PDCs) exert multiple functions, including production of interferon (IFN)-alpha as effector cells and regulation of T-cell responses as mature DCs. Here we review recent data obtained in situ showing that PDCs accumulate in lesions of type I IFN-related disorders (virus infections and lupus erythematosus), Th2 cell-dominated allergic reactions, and ovarian carcinoma. These results demonstrate that PDCs do migrate to peripheral tissues during inflammation, which lends further support to the view that PDCs most likely are important players in innate and adaptive immunity in vivo. Future research should aim at defining the exact pathogenic or defense roles of PDCs in such disorders and determine whether these cells are potential targets for therapeutic intervention in microbial infections, allergy, autoimmunity, or cancer.

Putative regulatory T cells are impaired in cord blood from neonates with hereditary allergy risk

The hygiene hypothesis implies that the increasing prevalence of allergy in ‘westernized’ countries is explained by reduced bacterial exposure in early life, but the underlying mechanism remains elusive. We therefore wanted to study the effect of bacterial lipopolysaccharide (LPS) on the generation of regulatory T (TR) cells in neonates, and to analyze differences between neonates with allergy risk because of a family history of atopy (FH+) and controls without such hereditary risk (FH−). Cord blood mononuclear cells from the FH+ and FH− groups were stimulated with β‐lactoglobulin in the presence of LPS. T‐cell phenotypes suggestive of TR cells [CD25+, CD25high and integrin (CD103+)], and the intracellular proliferation antigen Ki‐67 were quantified by flow cytometry. Release of the immunosuppressive cytokine transforming growth factor β1 (TGF‐β1) from its inactive complex was determined by enzyme‐linked immunosorbent assay. The analyses revealed the generation of T‐cell phenotypes suggestive of TR cells including a CD25high T‐cell subset which was inversely related to T‐cell proliferation (r = −0.54, p < 0.05) and to activation‐induced release of TGF‐β1 (r = −0.80, p < 0.001). The CD25high T‐cell subset tended to be impaired in the FH+ group (% of CD3+ T cells: FH+, 5.1% vs. FH−, 12.6%), and notably, the FH+ group showed a significantly reduced capacity for generation of both CD25+ (FH+, 16.2% vs. FH−, 34.9%; p < 0.01) and T cells (FH+, 2.1% vs. FH−, 3.9%; p < 0.05). Our findings suggested that early‐life exposure to a dietary antigen in the presence of LPS might modulate the immune system by generating TR cells. This capacity was impaired in neonates with hereditary allergy risk, but clinical follow‐up will be required to determine a possible effect on allergy emergence.

Depletion of CD4+CD25+CD127lo regulatory T cells does not increase allergen‐driven T cell activation

Background It has been suggested that allergic diseases are caused by defective suppression of allergen‐specific Th2 cells by CD4+CD25+ regulatory T cells. However, such studies have been hampered by the difficulty in distinguishing regulatory T cells from CD25‐expressing activated T cells. Recently, it was shown that conventional T cells expressed high levels of CD127, whereas regulatory T cells were CD127lo, allowing discrimination between these distinct T cell subpopulations.

Plasmacytoid Dendritic Cells Induce a Distinct Cytokine Pattern in Virus-Specific CD4+ Memory T Cells that is Modulated by CpG Oligodeoxynucleotides

Inherent properties of dendritic cell (DC) subsets are important in the regulation of naïve T‐cell differentiation (e.g. Th1 versus Th2 cells), whereas effector memory T cells are believed to produce a fixed cytokine repertoire independent of the type of antigen presenting cell. Here we show that two distinct human DC subsets, plasmacytoid DC (PDC) and myeloid CD11c+ DC, induced autologous mumps virus‐specific memory CD4+ T cells to produce markedly different cytokine patterns upon antigen stimulation. PDC stimulated the T cells to produce γ‐interferon (IFN‐γ) and interleukin‐(IL)‐10, whereas CD11c+ DC induced lower levels of IFN‐γ, virtually no IL‐10, but significant levels of IL‐5. Analysis of intracellular cytokine production showed simultaneous production of IL‐10 and IFN‐γ in mumps‐specific T cells activated by PDC, a cytokine pattern similar to that described for Th1‐like regulatory cells. Introduction of CpG oligodeoxynucleotides in PDC/T‐cell co‐cultures had synergistic effect on virus‐dependent IFN‐γ production, whereas the other cytokines remained unchanged. Together, our results show that the type of DC involved in reactivation of previously primed T cells may have significant impact on the resulting cytokine response and suggest that targeting of viral antigens and adjuvant to specific DC subsets should be considered in the design of therapeutic antiviral vaccines.