Joshua Beilke

Adaptive immune features of natural killer cells

In an adaptive immune response, naive T cells proliferate during infection and generate long-lived memory cells that undergo secondary expansion after a repeat encounter with the same pathogen. Although natural killer (NK) cells have traditionally been classified as cells of the innate immune system, they share many similarities with cytotoxic T lymphocytes. We use a mouse model of cytomegalovirus infection to show that, like T cells, NK cells bearing the virus-specific Ly49H receptor proliferate 100-fold in the spleen and 1,000-fold in the liver after infection. After a contraction phase, Ly49H-positive NK cells reside in lymphoid and non-lymphoid organs for several months. These self-renewing ‘memory’ NK cells rapidly degranulate and produce cytokines on reactivation. Adoptive transfer of these NK cells into naive animals followed by viral challenge results in a robust secondary expansion and protective immunity. These findings reveal properties of NK cells that were previously attributed only to cells of the adaptive immune system.

T-bet–dependent S1P5 expression in NK cells promotes egress from lymph nodes and bone marrow

During a screen for ethylnitrosourea-induced mutations in mice affecting blood natural killer (NK) cells, we identified a strain, designated Duane, in which NK cells were reduced in blood and spleen but increased in lymph nodes (LNs) and bone marrow (BM). The accumulation of NK cells in LNs reflected a decreased ability to exit into lymph. This strain carries a point mutation within Tbx21 (T-bet), which generates a defective protein. Duane NK cells have a 30-fold deficiency in sphingosine-1-phosphate receptor 5 (S1P5) transcript levels, and S1P5-deficient mice exhibit an egress defect similar to Duane. Chromatin immunoprecipitation confirms binding of T-bet to the S1pr5 locus. S1P-deficient mice exhibit a more severe NK cell egress block, and the FTY720-sensitive S1P1 also plays a role in NK cell egress from LNs. S1P5 is not inhibited by CD69, a property that may facilitate trafficking of activated NK cells to effector sites. Finally, the accumulation of NK cells within BM of S1P-deficient mice was associated with reduced numbers in BM sinusoids, suggesting a role for S1P in BM egress. In summary, these findings identify S1P5 as a T-bet–induced gene that is required for NK cell egress from LNs and BM.

NK cells promote islet allograft tolerance via a perforin-dependent mechanism

Although major histocompatibility complex (MHC) class II–restricted CD4 T cells are well appreciated for their contribution to peripheral tolerance to tissue allografts, little is known regarding MHC class I–dependent reactivity in this process. Here we show a crucial role for host MHC class I–dependent NK cell reactivity for allograft tolerance in mice induced through either costimulation blockade using CD154-specific antibody therapy or by targeting LFA-1 (also known as CD11a). Tolerance induction absolutely required host expression of MHC class I, but was independent of CD8 T cell–dependent immunity. Rather, tolerance required innate immunity involving NK1.1+ cells, but was independent of CD1d-restricted NKT cells. Therefore, NK cells seem to be generally required for induction of tolerance to islet allografts. Additional studies indicate that CD154-specific antibody–induced allograft tolerance is perforin dependent. Notably, NK cells that are perforin competent are sufficient to restore allograft tolerance in perforin-deficient recipients. Together, these results show an obligatory role for NK cells, through perforin, for induction of tolerance to islet allografts.Note: In the version of this article initially published, the authors inadvertently misquoted a study as evidence that mouse NKT cells can express CD154 (ref. 29). Rather, the cited study concerned CD40-CD40L interactions in human NK cells. By misquoting this study, the authors also omitted an appropriate reference regarding prior evidence of CD40-CD40L interactions by murine NKT cells (Kitamura, H. et al., J. Exp. Med. 189, 1121; 1999). These errors have been corrected in the PDF version.

Evidence for a primary islet autoantigen (preproinsulin 1) for insulitis and diabetes in the nonobese diabetic mouse

It has been reported that an insulin 2 gene knockout, when bred onto nonobese diabetic (NOD) mice, accelerates diabetes. We produced insulin 1 gene knockout congenic NOD mice. In contrast to insulin 2, diabetes and insulitis were markedly reduced in insulin 1 knockout mice, with decreased and delayed diabetes in heterozygous females and no insulitis and diabetes in most homozygous female mice. Lack of insulitis was found for insulin 1 female homozygous knockout mice at 8, 12, and 37 weeks of age. Despite a lack of insulitis, insulin 1 homozygous knockout mice spontaneously expressed insulin autoantibodies. Administration of insulin peptide B:9-23 of both insulin 1 and 2 to NOD mice induced insulin autoantibodies. Insulin 1 is not the only lymphocytic target of NOD mice. Insulin 1 homozygous knockout islets, when transplanted into recently diabetic wild-type NOD mice, became infiltrated with lymphocytes and only transiently reversed diabetes. These observations indicate that loss of either insulin gene can influence progression to diabetes of NOD mice and suggest that the preproinsulin 1 gene is crucial for the spontaneous development of NOD insulitis and diabetes.

Proinflammatory cytokine signaling required for the generation of natural killer cell memory

Responsiveness to interleukin-12, but not interferon-γ, is essential for the generation of long-lived natural killer cells capable of responding to secondary viral infection.

Homeostatic proliferation generates long-lived natural killer cells that respond against viral infection

Like memory T cells, natural killer cells that undergo homeostatic expansion in mice self-renew and retain the ability to respond to subsequent viral infection.

CD4-Dependent Generation of Dominant Transplantation Tolerance Induced by Simultaneous Perturbation of CD154 and LFA-1 Pathways

CD154 and LFA-1 (CD11a) represent conceptually distinct pathways of receptor/ligand interactions (costimulation and adhesion/homing, respectively) that have been effectively targeted to induce long-term allograft acceptance and tolerance. In the current study, we determined the relative efficacy and nature of tolerance induced by mAbs specific for these pathways. In vitro analysis indicated that simultaneous targeting of CD154 and LFA-1 resulted in profound inhibition of alloreactivity, suggesting that combined anti-CD154/anti-LFA-1 therapy could be highly effective in vivo. Thus, we evaluated combining mAb therapies targeting CD154 and LFA-1 for inducing transplantation tolerance to pancreatic islet allografts. Monotherapy with either anti-CD154 or anti-LFA-1 was partially effective for inducing long-term allograft survival, whereas the combination resulted in uniform allograft acceptance in high-responder C57BL/6 recipients. This combined therapy was not lymphocyte depleting and did not require the long-term deletion of donor-reactive T lymphocytes to maintain allograft survival. Importantly, combined anti-CD154/anti-LFA therapy uniquely resulted in “dominant” transplantation tolerance. Therefore, simultaneous perturbation of CD154 and LFA-1 molecules can result in profound tolerance induction not accomplished through individual monotherapy approaches. Furthermore, results show that such regulatory tolerance can coexist with the presence of robust anti-donor reactivity, suggesting that active tolerance does not require a corresponding deletion of donor-reactive T cells. Interestingly, although the induction of this regulatory state was highly CD4 dependent, the adoptive transfer of tolerance was less CD4 dependent in vivo.

Immune memory redefined: characterizing the longevity of natural killer cells.

Summary:  Natural killer (NK) cells respond rapidly to transformed, stressed, or virally infected cells and provide a first‐line immune defense against pathogen invasion and cancer. Thought to involve short‐lived effector cells that are armed for battle, NK cells were not previously known to contribute in recall responses to pathogen re‐encounter. Here, we highlight recent discoveries demonstrating that NK cells are not limited to driving primary immune responses to foreign antigen but can mount secondary responses contributing to immune memory. We also further characterize the phenotype and function of long‐lived memory NK cells generated during viral infection.

Adenovirus-mediated HIF-1α gene transfer promotes repair of mouse airway allograft microvasculature and attenuates chronic rejection

Chronic rejection, manifested as small airway fibrosis (obliterative bronchiolitis [OB]), is the main obstacle to long-term survival in lung transplantation. Recent studies demonstrate that the airways involved in a lung transplant are relatively hypoxic at baseline and that OB pathogenesis may be linked to ischemia induced by a transient loss of airway microvasculature. Here, we show that HIF-1α mediates airway microvascular repair in a model of orthotopic tracheal transplantation. Grafts with a conditional knockout of Hif1a demonstrated diminished recruitment of recipient-derived Tie2⁺ angiogenic cells to the allograft, impaired repair of damaged microvasculature, accelerated loss of microvascular perfusion, and hastened denudation of epithelial cells. In contrast, graft HIF-1α overexpression induced via an adenoviral vector prolonged airway microvascular perfusion, preserved epithelial integrity, extended the time window for the graft to be rescued from chronic rejection, and attenuated airway fibrotic remodeling. HIF-1α overexpression induced the expression of proangiogenic factors such as Sdf1, Plgf, and Vegf, and promoted the recruitment of vasoreparative Tie2⁺ cells. This study demonstrates that a therapy that enhances vascular integrity during acute rejection may promote graft health and prevent chronic rejection.

Increased NF‐κB activity in B cells and bone marrow‐derived dendritic cells from NOD mice

Type 1 diabetes results from the breakdown of peripheral tolerance. As regulators of T cell activation, antigen‐presenting cells (APC) modulate peripheral tolerance and hence contribute to theimmune dysregulation characteristic of insulin‐dependent diabetes mellitus (IDDM). We initially observed an increased importance of NOD B cell APC function in a T cell priming assay as compared to non‐autoimmune strains. Consistent with this increased APC function, we found that NF‐κB nuclear translocation is increased in unmanipulated NOD and NOD.B10Sn‐H2b B cells and that, inaddition, NOD B cells are more sensitive to NF‐κB‐activating stimuli. We obtained similar results using NOD bone marrow‐derived dendritic cell (BMDC) cultures. As costimulatory molecules havebeen shown to be NF‐κB responsive, we examined the expression of these markers on NOD APC. Both B cells and BMDC expressed elevated levels of CD80 and CD40. Finally, NOD B cells provided better allostimulation than B cells from non‐autoimmune strains. Therefore, hyperactivation of NF‐κB and increased expression of CD80 and CD40 by NOD B cells and BMDC may be a contributing factor in the selection of effector T cells observed in IDDM.