SUMMARY How type I/II interferons prevent periodic reemergence of latent pathogens in tissues of diverse cell-types remains unknown. Using homogenous neuron cultures latently-infected with herpes simplex virus-1, we show that extrinsic type I or II interferon act directly on neurons to induce unique gene expression signatures and inhibit the reactivation-specific burst of viral genome-wide transcription called Phase I. Surprisingly, interferons suppressed reactivation only during a limited period early in Phase I preceding productive virus growth. Sensitivity to type II interferon was selectively lost if viral ICP0, which normally accumulates later in Phase I, was expressed before reactivation. Thus, interferons suppress reactivation by preventing initial expression of latent genomes but are ineffective once Phase I viral proteins accumulate, limiting interferon action. This demonstrates that inducible reactivation from latency is only transiently sensitive to interferon. Moreover, it illustrates how latent pathogens escape host immune control to periodically replicate by rapidly deploying an interferon-resistant state.

Studies of infection in Drosophila melanogaster provide insight into both mechanisms of host resistance and tolerance of pathogens. However, research into the pathways involved in these processes has been limited by the relatively few metrics that can be used to measure sickness and health throughout the course of infection. Here we report measurements of infection-related declines in flies' performance on two different behavioral assays. D. melanogaster are slower to recover from a chill-induced coma during infection with either Listeria monocytogenes or Streptococcus pneumoniae. L. monocytogenes infection also impacts flies' performance during a negative geotaxis assay, revealing a decline in their rate of climbing as part of their innate escape response after startle. In addition to providing new measures for assessing health, these assays also suggest pathological consequences of and metabolic shifts that may occur over the course of an infection.

Because of the perception that depleting hematopoietic grafts of T cells will result in poorer immune recovery and in increased risk of graft rejection, pure hematopoietic stem cells (HSC), which avoid the potentially lethal complication of graft-versus-host disease (GVHD), have not been used for allogeneic hematopoietic cell transplantation (HCT) in humans. Ideal grafts should contain HSC plus mature cells that confer only the benefits of protection from pathogens and suppression of malignancies. This goal requires better understanding of the effects of each blood cell type and its interactions during engraftment and immune regeneration. Here, we studied hematopoietic reconstitution post-HCT, comparing grafts of purified HSC with grafts supplemented with T cells in a minor histocompatibility antigen (mHA)-mismatched mouse model. Cell counts, composition, and chimerism of blood and lymphoid organs were evaluated and followed intensively through the first month, and then subsequently for up to 1 yr. Throughout this period, recipients of pure HSC demonstrated superior total cell recovery and lymphoid reconstitution compared with recipients of T cell-containing grafts. In the latter, rapid expansion of T cells occurred, and suppression of hematopoiesis derived from donor HSC was observed. Our findings demonstrate that even early post-HCT, T cells retard donor HSC engraftment and immune recovery. These observations contradict the postulation that mature donor T cells provide important transient immunity and facilitate HSC engraftment.immune reconstitution | graft composition | mice

We describe a primary neuronal culture system suitable for molecular characterization of herpes simplex virus type 1 (HSV-1) infection, latency, and reactivation. While several alternative models are available, including infections of live animal and explanted ganglia, these are complicated by the presence of multiple cell types, including immune cells, and difficulties in manipulating the neuronal environment. The highly pure neuron culture system described here can be readily manipulated and is ideal for molecular studies that focus exclusively on the relationship between the virus and host neuron, the fundamental unit of latency. As such it allows for detailed investigations of both viral and neuronal factors involved in the establishment and maintenance of HSV-1 latency and in viral reactivation induced by defined stimuli.

T cells are widely used to promote engraftment of hematopoietic stem cells (HSCs) during an allogeneic hematopoietic cell transplantation. Their role in overcoming barriers to HSC engraftment is thought to be particularly critical when patients receive reduced doses of preparative chemotherapy and/or radiation compared with standard transplantations. In this study, we sought to delineate the effects CD4+ cells on engraftment and blood formation in a model that simulates clinical hematopoietic cell transplantation by transplanting MHC-matched, minor histocompatibility–mismatched grafts composed of purified HSCs, HSCs plus bulk T cells, or HSCs plus T cell subsets into mice conditioned with low-dose irradiation. Grafts containing conventional CD4+ T cells caused marrow inflammation and inhibited HSC engraftment and blood formation. Posttransplantation, the marrows of HSCs plus CD4+ cell recipients contained IL-12–secreting CD11c+ cells and IFN-γ–expressing donor Th1 cells. In this setting, host HSCs arrested at the short-term stem cell stage and remained in the marrow in a quiescent cell cycling state (G0). As a consequence, donor HSCs failed to engraft and hematopoiesis was suppressed. Our data show that Th1 cells included in a hematopoietic allograft can negatively impact HSC activity, blood reconstitution, and engraftment of donor HSCs. This potential negative effect of donor T cells is not considered in clinical transplantation in which bulk T cells are transplanted. Our findings shed new light on the effects of CD4+ T cells on HSC biology and are applicable to other pathogenic states in which immune activation in the bone marrow occurs such as aplastic anemia and certain infectious conditions.