Impaired IFN-γ production and proliferation of NK cells in multiple sclerosis.

NK cells are multicompetent lymphocytes of the innate immune system with a central role in host defense and immune regulation. Studies in experimental animal models of multiple sclerosis (MS) provided evidence for both pathologic and protective effects of NK cells. Humans harbor two functionally distinct NK-cell subsets exerting either predominantly cytotoxic (CD56(dim)CD16(+)) or immunoregulatory (CD56(bright)CD16(-)) functions. We analyzed these two subsets and their functions in the peripheral blood of untreated patients with relapsing-remitting MS compared with healthy blood donors. While ex vivo frequencies of CD56(bright)CD16(-) and CD56(dim)CD16(+) NK cells were similar in patients and controls, we found that cytokine-driven in vitro accumulation and IFN-γ production of CD56(bright)CD16(-) NK cells but not of their CD56(dim)CD16(+) counterparts were substantially diminished in MS. Impaired expansion of CD56(bright)CD16(-) NK cells was cell intrinsic because the observed effects could be reproduced with purified NK cells in an independent cohort of patients and controls. In contrast, cytolytic NK-cell activity toward the human erythromyeloblastoid leukemia cell line K562, the allogeneic CD4(+) T cell line CEM and allogeneic primary CD4(+) T-cell blasts was unchanged. Thus, characteristic functions of CD56(bright)CD16(-) NK cells, namely cytokine-induced NK cell expansion and IFN-γ production, are compromised in the NK cell compartment of MS patients.

Elevated Epstein-Barr virus-encoded nuclear antigen-1 immune responses predict conversion to multiple sclerosis.

OBJECTIVE: The aims of the study were to determine the immune responses to candidate viral triggers of multiple sclerosis (MS) in patients with clinically isolated syndromes (CISs), and to evaluate their potential value in predicting conversion to MS. METHODS: Immune responses to Epstein-Barr virus (EBV), human herpesvirus 6, cytomegalovirus (HCMV), and measles were determined in a cohort of 147 CIS patients with a mean follow-up of 7 years and compared with 50 demographically matched controls. RESULTS: Compared with controls, CIS patients showed increased humoral (p < 0.0001) and cellular (p = 0.007) immune responses to the EBV-encoded nuclear antigen-1 (EBNA1), but not to other EBV-derived proteins. Immunoglobulin G (IgG) responses to other virus antigens and frequencies of T cells specific for HCMV and influenza virus gene products were unchanged in CIS patients. EBNA1 was the only viral antigen with which immune responses correlated with number of T2 lesions (p = 0.006) and number of Barkhof criteria (p=0.001) at baseline, and with number of T2 lesions (p = 0.012 at both 1 and 5 years), presence of new T2 lesions (p = 0.003 and p = 0.028 at 1 and 5 years), and Expanded Disability Status Scale score (p = 0.015 and p = 0.010 at 1 and 5 years) during follow-up. In a univariate Cox regression model, increased EBNA1-specific IgG responses predicted conversion to MS based on McDonald criteria (hazard ratio [95% confidence interval], 2.2 [1.2-4.3]; p = 0.003). INTERPRETATION: Our results indicate that elevated immune responses toward EBNA1 are selectively increased in CIS patients and suggest that EBNA1-specific IgG titers could be used as a prognostic marker for disease conversion and disability progression.

Human NK cells kill resting but not activated microglia via NKG2D- and NKp46-mediated recognition.

Microglia are resident macrophage-like APCs of the CNS. To avoid escalation of inflammatory processes and bystander damage within the CNS, microglia-driven inflammatory responses need to be tightly regulated and both spatially and temporally restricted. Following traumatic, infectious, and autoimmune-mediated brain injury, NK cells have been found in the CNS, but the functional significance of NK cell recruitment and their mechanisms of action during brain inflammation are not well understood. In this study, we investigated whether and by which mechanisms human NK cells might edit resting and activated human microglial cells via killing in vitro. IL-2-activated NK cells efficiently killed both resting allogeneic and autologous microglia in a cell-contact-dependent manner. Activated NK cells rapidly formed synapses with human microglial cells in which perforin had been polarized to the cellular interface. Ab-mediated NKG2D and NKp46 blockade completely prevented the killing of human microglia by activated NK cells. Up-regulation of MHC class I surface expression by TLR4 stimulation protected microglia from NK cell-mediated killing, whereas MHC class I blockade enhanced cytotoxic NK cell activity. These data suggest that brain-infiltrating NK cells might restrict innate and adaptive immune responses within the human CNS via elimination of resting microglia.

Silk fibroin microtubes for blood vessel engineering.

Currently available synthetic grafts demonstrate moderate success at the macrovascular level, but fail at the microvascular scale (<6mm inner diameter). We report on the development of silk fibroin microtubes for blood vessel repair with several advantages over existing scaffold materials/designs. These microtubes were prepared by dipping straight lengths of stainless steel wire into aqueous silk fibroin, where the addition of poly(ethylene oxide) (PEO) enabled control of microtube porosity. The microtube properties were characterized in terms of pore size, burst strength, protein permeability, enzymatic degradation, and cell migration. Low porosity microtubes demonstrated superior mechanical properties in terms of higher burst pressures, but displayed poor protein permeability; whereas higher porosity tubes had lower burst strengths but increased permeability and enhanced protein transport. The microtubes also exhibited cellular barrier functions as low porosity tubes prevented outward migration of GFP-transduced HUVECs, while the high porosity microtubes allowed a few cells per tube to migrate outward during perfusion. When combined with the biocompatible and suturability features of silk fibroin, these results suggest that silk microtubes, either implanted directly or preseeded with cells, are an attractive biomaterial for microvascular grafts.