Paul C. Roberts

Essential Role for the dsRNA-Dependent Protein Kinase PKR in Innate Immunity to Viral Infection

The double-stranded (ds) RNA-dependent protein kinase PKR is considered to play an important role in interferons (IFNs) response to viral infection. Here, we demonstrate that mice lacking PKR are predisposed to lethal intranasal infection by the usually innocuous vesicular stomatitis virus, and also display increased susceptibility to influenza virus infection. Our data indicate that in normal cells, PKR primarily prevents virus replication by inhibiting the translation of viral mRNAs through phosphorylation of eIF2alpha, while concomitantly assisting in the production of autocrine IFN and the establishment of an antiviral state. These results show that PKR is an essential component of innate immunity that acts early in host defense prior to the onset of IFN counteraction and the acquired immune response.

NK Cells Inhibit T Cell Proliferation via p21-Mediated Cell Cycle Arrest

NK cells have been shown to influence immune responses via direct interaction with cells of the adaptive immune system, such as dendritic cells, B cells, and T cells. A role for NK cells in down-regulation of T cell responses has been implicated in several studies; however, the underlying mechanism of this suppression has remained elusive. In this study we show that dark Agouti rat NK cells inhibit syngeneic T cell proliferation via up-regulation of the cell cycle inhibitor, p21, resulting in a G0/G1 stage cell cycle arrest. The inhibition is cell-cell contact dependent, reversible, and Ag nonspecific. Interestingly, NK cells do not inhibit IL-2 secretion or IL-2R up-regulation and do not induce T cell death. Thus, our results show that NK cells do not affect early T cell activation events, but specifically inhibit T cell proliferation by direct interaction with T cells. Our findings suggest that NK cells may play an important role in maintaining immune homeostasis by directly regulating clonal expansion of activated T cells. This novel mechanism of T cell regulation by NK cells provides insight into NK cell-mediated regulation of adaptive immunity and provides a mechanistic link between NK cell function and suppression of T cell responses.

Characterization of a subset of bone marrow-derived natural killer cells that regulates T cell activation in rats

We report that bone marrow‐derived natural killer (BMNK) cells from DA or F344 rats inhibit PMA/ionomycin‐induced T cell proliferation. These NK‐regulatory cells are NKR‐P1Adim, whereas a minor subpopulation is NKR‐P1Abright. Only the NKR‐P1Adim BMNK cells inhibit T cell proliferation. If activated with rat Con A supernatant, the NKR‐P1Adim cells become NKR‐P1Abright and lose the ability to inhibit T cell proliferation. In contrast to BMNK cells, all DA and F344 rat NK cells isolated from the blood, spleen, cervical, or mesenteric lymph nodes or Peyer’s patches are NKR‐P1Abright and lack the ability to inhibit T cell proliferation. Inhibition of T cell proliferation correlates with significant down‐regulation of CD3, suggesting that this may be the mechanism through which the NKR‐P1Adim cells mediate suppression. The nitric oxide synthase inhibitor NG‐monomethyl‐arginine acetate‐abrogated NKR‐P1Adim cell inhibition of T cell proliferation. We conclude that rat bone marrow NKR‐P1Adim cells represent a unique population that may play a role in maintaining immune homeostasis by regulating the clonal expansion of activated T cells.

Tailored vaccines targeting the elderly using whole inactivated influenza vaccines bearing cytokine immunomodulators.

Influenza and its complications disproportionately affect the elderly, leading to high morbidity and mortality in this ever-increasing population. Despite widespread vaccination efforts, the current influenza vaccines are less effective in the elderly; hence newer vaccine strategies are needed to improve their efficacy in this age group. We have previously shown that co-presentation of cytokines on the surface of inactivated influenza virus particles affords better protection from lethal homotypic viral challenge in young adult mice than conventional non-adjuvanted whole inactivated vaccine. Here, we determined the efficacy of these vaccine formulations in Balb/c mice aged to 17 months (aged mice) along with the addition of a membrane-bound interleukin-12 (IL-12) vaccine formulation. Our investigations found that a single low-dose intramuscular vaccination with inactivated whole influenza vaccine co-presenting IL-12 was sufficient to provide enhanced protection from subsequent influenza challenge as compared with non-adjuvanted whole inactivated vaccine. Our results indicate that incorporation of cytokines such as IL-12 in a membrane-bound formulation in whole inactivated vaccine may provide a means to lower the vaccine dose while eliciting enhanced protective responses in the elderly, an age group that responds poorly to current vaccination regimens.

Regulation of Adaptive Immunity by Cells of the Innate Immune System: Bone Marrow Natural Killer Cells Inhibit T Cell Proliferation

Natural killer (NK) cells represent the third largest population of lymphocytes after T and B cells and are derived from the same precursor cell, although they do not express antigen-specific receptors (Yokoyama et al., 2004). However, they can distinguish normal host cells from virus-infected or tumor cells and lyse the latter without prior immunological sensitization — hence the name “natural killer” cell (Trinchieri, 1989). It was determined that the NK cells recognize target cells because the latter are deficient in, or lack, the expression of host major histocompatibility (MHC) class I molecules (Karre et al., 1986).