Recruitment of Activation Receptors at Inhibitory NK Cell Immune Synapses

Natural killer (NK) cell activation receptors accumulate by an actin-dependent process at cytotoxic immune synapses where they provide synergistic signals that trigger NK cell effector functions. In contrast, NK cell inhibitory receptors, including members of the MHC class I-specific killer cell Ig-like receptor (KIR) family, accumulate at inhibitory immune synapses, block actin dynamics, and prevent actin-dependent phosphorylation of activation receptors. Therefore, one would predict inhibition of actin-dependent accumulation of activation receptors when inhibitory receptors are engaged. By confocal imaging of primary human NK cells in contact with target cells expressing physiological ligands of NK cell receptors, we show here that this prediction is incorrect. Target cells included a human cell line and transfected Drosophila insect cells that expressed ligands of NK cell activation receptors in combination with an MHC class I ligand of inhibitory KIR. The two NK cell activation receptors CD2 and 2B4 accumulated and co-localized with KIR at inhibitory immune synapses. In fact, KIR promoted CD2 and 2B4 clustering, as CD2 and 2B4 accumulated more efficiently at inhibitory synapses. In contrast, accumulation of KIR and of activation receptors at inhibitory synapses correlated with reduced density of the integrin LFA-1. These results imply that inhibitory KIR does not prevent CD2 and 2B4 signaling by blocking their accumulation at NK cell immune synapses, but by blocking their ability to signal within inhibitory synapses

Campylobacter fetus Bacteremia Revealed by Cellulitis without Gastrointestinal Symptoms in the Context of Acquired Hypogammaglobulinemia: A Report of Three Cases

Campylobacter fetus bacteremia is rare and occurs mainly in patients with immunosuppression. This infection, which often involves secondary localizations has already been reported in some primary humoral immune deficiencies. We describe three cases of severe infection due to C. fetus with cellulitis at presentation, but without any gastrointestinal symptoms, occurring in patients with acquired hypogammaglobulinemia

Pattern of DAP12 Expression in Leukocytes from Both Healthy and Systemic Lupus Erythematosus Patients

DAP12 is an ITAM-bearing transmembrane adaptor originally identified on the surface of Natural Killer cells. A broad expression among other immune cells was later found in myeloid and lymphoid cells. However, data on DAP12 expression pattern rely only on immunoblot and microarray analysis. Here, we describe the generation and the characterization of an anti-DAP12 monoclonal antibody. Using this novel reagent, we show that DAP12 expression is restricted to innate immune cells in basal condition. Since a decreased expression of DAP12 has been suggested in NK cells of systemic lupus erythematosus patients, we have further investigated the NK cell receptor repertoire and leukocyte expression of DAP12 in these patients and no major changes were detectable when compared to controls

Pathologies Associated with Serum IgG4 Elevation

Statement of Purpose. IgG4-related disease (IgG4-RD) is usually associated to an increase of serum IgG4 levels. However other conditions have also been associated to high serum IgG4 levels. Methods. All IgG subclasses analyses performed in our hospital over a one-year period were analyzed. When IgG4 level were over 1.35 g/L, the patient’s clinical observation was analyzed and both final diagnosis and reason leading to IgG subclasses analysis were recorded. Only polyclonal increases of IgG4 were considered. Summary of the Results. On 646 IgG subclass analysis performed, 59 patients had serum IgG4 over 1.35 g/L. The final diagnosis associated to serum IgG4 increase was very variable. Most patients (25%) presented with repeated infections, 13.5% with autoimmune diseases, and 10% with IgG4-RD. Other patients presented with cancer, primary immune deficiencies, idiopathic interstitial lung disease, cystic fibrosis, histiocytosis, or systemic vasculitis and 13.5% presented with various pathologies or no diagnosis. Mean IgG4 levels and IgG4/IgG ratio were higher in IgG4-RD than in other pathologies associated to elevated IgG4 levels. Conclusions. Our study confirms that elevation of serum IgG4 is not specific to IgG4-RD. Before retaining IgG4-RD diagnosis in cases of serum IgG4 above 1.35 g/L, several other pathological conditions should be excluded

Natural killer cells in human autoimmune diseases

Natural killer (NK) cells have been implicated in tumour surveillance and in the early control of several microbial infections. In autoimmune disease their involvement in these processes has been evaluated in animal models, with conflicting results. Both a disease-controlling and a disease-promoting role have been suggested. In human autoimmune disease only a few studies, mainly descriptive, have demonstrated qualitative and quantitative modification of NK cells. These changes were observed on blood- or tissue-infiltrating NK cells. Taken together with our expanding knowledge of the genetical variability of NK cell receptors and NK cell physiology, these findings pave the way for the dissection of the role of NK cells in human autoimmune diseases. NK cells may be directly involved in these diseases through their potential autoreactivity or through their interaction with dendritic cells, macrophages or T lymphocytes, thereby inducing excessive inflammation or favouring the adaptive autoimmune response. Thus, NK cells may be implicated in the onset, the maintenance or the progression of autoimmune diseases. Some reports also suggest the involvement of NK cells in the treatment of human autoimmune disease by biotherapies. All these observations suggest that NK cells are involved in the complex processes of autoimmune diseases. Nevertheless, further careful analysis of NK cells at different steps of these diseases, in different tissues and through combined genetical and functional studies will contribute to a better understanding of their role in autoimmune diseases. This knowledge might allow the development of new therapeutic strategies based on NK cells for the treatment of some autoimmune diseases

Infliximab in the treatment of refractory vasculitis secondary to hepatitis C-associated mixed cryoglobulinaemia

International audienc

CD2 accumulates more frequently at inhibitory synapses than at activating synapses.

<p>(A) Conjugates between IL-2 activated polyclonal human NK cells and 721.221-Cw15 cells or S2–LFA-3/Cw4 cells were formed and stained as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0003278#pone-0003278-g002" target="_blank">Figure 2</a>. Activating (Act.) and inhibitory (Inhib.) synapses were scored for clustering of CD2 at the zone of contact. The number of conjugates scored in each condition is indicated in parentheses. (B) Conjugates between activated NK cells and 721.221-Cw15 cells were allowed to form for 1 minute or 10 minutes as indicated, stained with the cyt42/43 antiserum and an anti-CD2 antibody as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0003278#pone-0003278-g002" target="_blank">Figure 2</a>, and scored for CD2 clustering.</p

Surface level of CD11a is reduced at inhibitory synapses.

<p>IL-2 activated polyclonal human NK cells and S2 cells expressing ICAM-1 and peptide-loaded HLA-Cw4 were mixed at 37°C for 10 minutes, fixed, permeabilized, and stained with cyt42/43 and a mAb to CD11a followed by the appropriate secondary antibodies. (A) Confocal microscope <i>z</i>-series were obtained, and single sections are shown. The cell labeled #1, which shows KIR expression and clustering, represents an inhibitory synapse while cell #2, which lacks KIR2DL1 expression, displays an activating synapse. (B) The fluorescence intensity was scanned around the perimeter of conjugated NK cells. Profiles labeled 1 and 2 are from the corresponding cells in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0003278#pone-0003278-g005" target="_blank">Figure 5A</a>. The third profile is another representative inhibitory synapse. The green and red lines represent the cyt42/43 and anti–CD11a fluorescence, respectively. Vertical red and blue lines mark the boundaries of cell contact as determined in DIC images. (C) Confocal <i>z</i>-stacks were used to create an <i>en face</i> view of the zone of cell contact in 2 inhibitory synapses. (D) The frequency of synapses displaying increased CD11a, reduced CD11a, or no change in CD11a intensity was determined for both activating and inhibitory synapses.</p

2B4 accumulates at both activating and inhibitory synapses.

<p>Activated NK cells were mixed with target cells at 37°C for 10 minutes, fixed, permeabilized, and stained with the cyt42/43 antiserum and a mAb to 2B4 followed by the appropriate secondary antibodies. (A) Mixed with .221-Cw15 target cells. Confocal microscope <i>z</i>-series were obtained, and single sections are shown. The cells labeled #1 and #3, which display KIR expression and clustering, represent inhibitory synapses while cell #2, which lacks KIR2DL1 expression, is an activating synapse. The NK cells without a number in the top image were not analyzed, because they did not appear to form tight conjugates with target cells. (B) The fluorescence intensity was scanned around the perimeter of conjugated NK cells. Profiles labeled 1, 2, and 3 are from the corresponding cells in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0003278#pone-0003278-g004" target="_blank">Figure 4A</a>. The green and blue lines represent the cyt42/43 and anti–2B4 fluorescence, respectively. Vertical red and blue lines mark the boundaries of cell contact as determined in DIC images. (C) Confocal <i>z</i>-stacks were used to create an <i>en face</i> view of the zone of cell contact in 2 inhibitory synapses.</p