Natural killer cell immunosuppressive function requires CXCR3-dependent redistribution within lymphoid tissues.

NK cell suppression of T cells is a key determinant of viral pathogenesis and vaccine efficacy. This process involves perforin-dependent elimination of activated CD4+ T cells during the first 3 days of infection. Although this mechanism requires cell-cell contact, NK cells and T cells typically reside in different compartments of lymphoid tissues at steady state. Here, we showed that NK cell suppression of T cells is associated with transient accumulation of NK cells within T cell-rich sites of the spleen during lymphocytic choriomeningitis virus infection. The chemokine receptor CXCR3 was required for this relocation and suppression of antiviral T cells. Accordingly, NK cell migration was mediated by type I IFN-dependent promotion of CXCR3 ligand expression. In contrast, adenoviral vectors that weakly induced type I IFN and did not stimulate NK cell inhibition of T cells also did not promote measurable redistribution of NK cells to T cell zones. Exogenous IFN rescued NK cell migration during adenoviral vector immunization. Thus, type I IFN and CXCR3 were critical for properly positioning NK cells to constrain antiviral T cell responses. Development of strategies to curtail migration of NK cells between lymphoid compartments may enhance vaccine-elicited immune responses.

Roles of natural killer cells in antiviral immunity.

Natural killer (NK) cells are important in immune defense against virus infections. This is predominantly considered a function of rapid, innate NK-cell killing of virus-infected cells. However, NK cells also prime other immune cells through the release of interferon gamma (IFN-γ) and other cytokines. Additionally, NK cells share features with long-lived adaptive immune cells and can impact disease pathogenesis through the inhibition of adaptive immune responses by virus-specific T and B cells. The relative contributions of these diverse and conflicting functions of NK cells in humans are poorly defined and likely context-dependent, thereby complicating the development of therapeutic interventions. Here we focus on the contributions of NK cells to disease in diverse virus infections germane to human health.

Generation of cellular immune memory and B-cell immunity is impaired by natural killer cells.

The goal of most vaccines is the induction of long-lived memory T and B cells capable of protecting the host from infection by cytotoxic mechanisms, cytokines and high-affinity antibodies. However, efforts to develop vaccines against major human pathogens such as HIV and HCV have not been successful, thereby highlighting the need for novel approaches to circumvent immunoregulatory mechanisms that limit the induction of protective immunity. Here, we show that mouse natural killer (NK) cells inhibit generation of long-lived virus-specific memory T- and B cells as well as virus-specific antibody production after acute infection. Mechanistically, NK cells suppressed CD4 T cells and follicular helper T cells (T(FH)) in a perforin-dependent manner during the first few days of infection, resulting in a weaker germinal centre (GC) response and diminished immune memory. We anticipate that innovative strategies to relieve NK cell-mediated suppression of immunity should facilitate development of efficacious new vaccines targeting difficult-to-prevent infections.

Homeotic Gene teashirt (tsh) has a neuroprotective function in amyloid-beta 42 mediated neurodegeneration.

BACKGROUND: Alzheimer's disease (AD) is a debilitating age related progressive neurodegenerative disorder characterized by the loss of cognition, and eventual death of the affected individual. One of the major causes of AD is the accumulation of Amyloid-beta 42 (Aß42) polypeptides formed by the improper cleavage of amyloid precursor protein (APP) in the brain. These plaques disrupt normal cellular processes through oxidative stress and aberrant signaling resulting in the loss of synaptic activity and death of the neurons. However, the detailed genetic mechanism(s) responsible for this neurodegeneration still remain elusive. METHODOLOGY/ PRINCIPLE FINDINGS: We have generated a transgenic Drosophila eye model where high levels of human Aß42 is misexpressed in the differentiating photoreceptor neurons of the developing eye, which phenocopy Alzheimer's like neuropathology in the neural retina. We have utilized this model for a gain of function screen using members of various signaling pathways involved in the development of the fly eye to identify downstream targets or modifiers of Aß42 mediated neurodegeneration. We have identified the homeotic gene teashirt (tsh) as a suppressor of the Aß42 mediated neurodegenerative phenotype. Targeted misexpression of tsh with Aß42 in the differentiating retina can significantly rescue neurodegeneration by blocking cell death. We found that Tsh protein is absent/ downregulated in the neural retina at this stage. The structure function analysis revealed that the PLDLS domain of Tsh acts as an inhibitor of the neuroprotective function of tsh in the Drosophila eye model. Lastly, we found that the tsh paralog, tiptop (tio) can also rescue Aß42 mediated neurodegeneration. CONCLUSIONS/SIGNIFICANCE: We have identified tsh and tio as new genetic modifiers of Aß42 mediated neurodegeneration. Our studies demonstrate a novel neuroprotective function of tsh and its paralog tio in Aß42 mediated neurodegeneration. The neuroprotective function of tsh is independent of its role in retinal determination.

Domain specific genetic mosaic system in the Drosophila eye.

Genetic mosaic approach is commonly used in the Drosophila eye by completely abolishing or misexpressing a gene within a subset of cells to unravel its role during development. Classical genetic mosaic approach involves random clone generation in all developing fields. Consequently, a large sample size needs to be screened to generate and analyze clones in specific domains of the developing eye. To address domain specific functions of genes during axial patterning, we have developed a system for generating mosaic clones by combining Gal4/UAS and flippase (FLP)/FRT system which will allow generation of loss-of-function as well as gain-of-function clones on the dorsal and ventral eye margins. We used the bifid-Gal4 driver to drive expression of UAS-FLP. This reagent can have multiple applications in (i) studying spatio-temporal function of a gene during dorso-ventral (DV) axis specification in the eye, (ii) analyzing genetic epistasis of genes involved in DV patterning, and (iii) conducting genome wide screens in a domain specific manner.