The small subset of CD56brightCD16- natural killer cells is selectively responsible for both cell proliferation and interferon-gamma production upon interaction with dendritic cells

The encounter of NK cells with dendritic cells (DC) undergoing maturation may result in the induction of NK cell proliferation. Whether such proliferation involves most NK cells or just a subset has yet to be determined. In the present study we analyzed the nature of such proliferating NK cells by combining carboxyfluorescein succinimidyl ester staining and double-fluorescence cytofluorimetric analysis. Freshly isolated peripheral blood NK cells cultured with LPS and immature DC underwent proliferation; however, proliferating cells were confined to a minor NK cell subset. This subset is characterized by the CD56(bright)CD16(-)NKG2A(+)KIR(-) surface phenotype (KIR, killer Ig-like receptor). This was further confirmed by the fact that, after cell sorting, only the CD56(bright) NK cells were able to proliferate in response to the DC stimulus, whereas the CD56(dull) were not. We also provide evidence that the CD56(bright) subset is the main source of IFN-gamma-producing NK cells, upon interaction with DC. The CD56(bright)CD16(-) NK cells express a panel of surface molecules including CD62L, CCR7 and CXCR3 that may allow their homing either to secondary lymphoid compartments or to inflamed tissues. This implies that, in vivo, the interactions between DC undergoing maturation and CD56(bright) NK cells may occur in different tissues and have different functional implications.     

Limbic network interactions leading to hyperexcitability in a model of temporal lobe epilepsy

In mouse brain slices that contain reciprocally connected hippocampus and entorhinal cortex (EC) networks, CA3 outputs control the EC propensity to generate experimentally induced ictal-like discharges resembling electrographic seizures. Neuronal damage in limbic areas, such as CA3 and dentate hilus, occurs in patients with temporal lobe epilepsy and in animal models (e.g., pilocarpine- or kainate-treated rodents) mimicking this epileptic disorder. Hence, hippocampal damage in epileptic mice may lead to decreased CA3 output function that in turn would allow EC networks to generate ictal-like events. Here we tested this hypothesis and found that CA3-driven interictal discharges induced by 4-aminopyridine (4AP, 50 microM) in hippocampus-EC slices from mice injected with pilocarpine 13-22 days earlier have a lower frequency than in age-matched control slices. Moreover, EC-driven ictal-like discharges in pilocarpine-treated slices occur throughout the experiment (< or = 6 h) and spread to the CA1/subicular area via the temporoammonic path; in contrast, they disappear in control slices within 2 h of 4AP application and propagate via the trisynaptic hippocampal circuit. Thus, different network interactions within the hippocampus-EC loop characterize control and pilocarpine-treated slices maintained in vitro. We propose that these functional changes, which are presumably caused by seizure-induced cell damage, lead to seizures in vivo. This process is facilitated by a decreased control of EC excitability by hippocampal outputs and possibly sustained by the reverberant activity between EC and CA1/subiculum networks that are excited via the temporoammonic path.     

Interleukin-7-engineered mesenchymal cells: in vitro effects on naive T-cell population.

T-cell homeostasis is regulated by several molecules; among these, interleukin (IL)-7 plays an essential role in the survival and homeostatic proliferation of peripheral naive T cells. In a previous study, we investigated whether human mesenchymal stromal cells (MSCs) could be engineered with the IL-7 gene to produce functional level of this cytokine. In the present study, we analyzed the impact of different quantities of IL-7 produced by MSCs on the survival and proliferation of a negative immunoselected naive (CD3(+)/CD45RA(+)) T-cell population. Co-cultivation of peripheral naive T cells with MSCs producing low (16 pg/mL) or high (1000 pg/mL) IL-7 levels or in the presence of exogenous IL-7 (0.01 ng/mL and 100 ng/mL) maintained the CD3(+)/CD45RA(+) naive T-cell phenotype. Chemokine receptor CCR7(+) expression was also maintained among this T-cell population. Naive T-cell molecular characteristics were maintained as assessed by the Vbeta spectratyping complexity score, which showed the maintenance of a broad T-cell repertoire. No Th1 or Th2 differentiation was observed, as assessed by interferon-gamma or IL-4 accumulation. In contrast, only MSCs producing high amounts of IL-7 caused increased activation (CD25 31.2% +/- 12% vs 10% +/- 3.5%; P < .05), proliferation (CD71 17.8+/-7% vs 9.3%+/-3, P < .05), apoptosis (assessed by annexin V: 18.6% +/- 5% vs 14.9% +/- 2.6%; P > .05), and the phase S cell cycle (15% vs 6.9%, P > .05). Exogenous IL-7 exhibited no significant effect. In conclusion, we demonstrated that IL-7 produced by MSCs has a dose-independent effect on naive T-cell survival while exerting a dose-dependent effect on activation/proliferation. Due to the continuous production of IL-7 by engineered cells, our system is more efficacious than exogenous IL-7.     

Apoptotic DNA binds to HLA class II molecules inhibiting antigen presentation and participating in the development of anti-inflammatory functional behavior of phagocytic macrophages

Resident macrophages are mainly responsible for the clearance of apoptotic cells from tissue by phagocytosis. Phagocytosis of apoptotic cells is not accompanied by activation of inflammatory mechanisms, unlike what happens when necrotic phenomena occur. We analyzed the effect of phagocytosis of apoptotic bodies on macrophage cell functions. After phagocytosis of apoptotic cells macrophages were unable to present an exogenous antigen to autologous antigen-specific T-cell lines. The inhibition was mediated by different mechanisms including binding of apoptotic DNA to human leukocyte antigen (HLA) class II molecules of macrophages, decreased expression of co-stimulatory molecules and increased secretion of tumor growth factor beta (TGFbeta). When dendritic cells were cultured with macrophages phagocytosing apoptotic cells, or with their supernatant, impaired dendritic cell antigen presenting activity and reduced tumor necrosis factor alpha (TNFalpha) secretion were found. Our results suggest that: (1) the phagocytosis of apoptotic bodies inhibits macrophage antigen presentation; (2) such inhibition is mediated by the binding of apoptotic DNA to macrophage HLA class II molecules as well as by the activation of biological mechanisms that induce an anti-inflammatory functional behavior in macrophages; and (3) macrophages phagocytosing apoptotic cells inhibit antigen presentation of neighboring dendritic cells via TGFbeta secretion. These events are likely related to the preservation of healthy tissues from the onset of inflammation.     

Role of Th1 and Th2 Cytokines in Immune Response to Uncomplicated Plasmodium falciparum Malaria

The relative balance between Th1 and Th2 cytokines appears crucial, since the role of cytokines has been evaluated in several studies by comparison of clinically heterogeneous groups of patients. The aim of this study is to determine the role of proinflammatory Th1 cytokines, interleukin-12 (IL-12) and gamma interferon (IFN-γ), and anti-inflammatory Th2 cytokines, IL-4 and IL-10, in a homogeneous group of patients with uncomplicated Plasmodium falciparum malaria. Levels of IL-12, IFN-γ, Il-4, and IL-10 in serum for 20 adult patients and 15 healthy control subjects were determined by an immunoenzymatic assay. Serum levels of Th1 cytokines, IL-12 (8.6 ± 2.8 pg/ml; controls, 3.2 ± 0.7 pg/ml) and IFN-γ (39.2 ± 67.6 pg/ml; controls, 8.4 ± 6.3 pg/ml), were significantly increased at admission; 3 days later, levels of IL-12 in serum remained significantly high (8.8 ± 2.6 pg/ml), whereas IFN-γ levels returned to control values. The anti-inflammatory response of Th2 cytokines (IL-10 and IL-4) was distinct. Levels of IL-10 in serum were not significantly increased at day 0 and day 3 (306.6 ± 200.4 pg/ml and 56.6 ± 38.4 pg/ml, respectively; controls, 17.4 ± 9.0 pg/ml). In contrast, levels of IL-4 in serum were not increased on admission (3.4 ± 1.2 pg/ml; controls, 2.4 ± 0.8 pg/ml), but at day 3 a moderate and significant increase of IL-4 levels was observed (4.5 ± 1.7 pg/ml). In conclusion, the increase of Th1 cytokine IL-12 and IFN-γ levels during the acute phase of uncomplicated P. falciparum malaria may reflect an early and effective immune response regulated by proinflammatory Th1 cytokines, and in particular IFN-γ may play a role in limiting progression from uncomplicated malaria to severe and life-threatening complications.