Transcriptional reprogramming of mature CD4⁺ helper T cells generates distinct MHC class II-restricted cytotoxic T lymphocytes.

TCRαß thymocytes differentiate into either CD8αß(+) cytotoxic T lymphocytes or CD4(+) helper T cells. This functional dichotomy is controlled by key transcription factors, including the helper T cell master regulator ThPOK, which suppresses the cytolytic program in major histocompatibility complex (MHC) class II-restricted CD4(+) thymocytes. ThPOK continues to repress genes of the CD8 lineage in mature CD4(+) T cells, even as they differentiate into effector helper T cell subsets. Here we found that the helper T cell fate was not fixed and that mature, antigen-stimulated CD4(+) T cells terminated expression of the gene encoding ThPOK and reactivated genes of the CD8 lineage. This unexpected plasticity resulted in the post-thymic termination of the helper T cell program and the functional differentiation of distinct MHC class II-restricted CD4(+) cytotoxic T lymphocytes.

Effect of High-Protein Diets on Integrated Myofibrillar Protein Synthesis before Anterior Cruciate Ligament Reconstruction: A Randomized Controlled Pilot Study.

Increasing dietary protein intake during periods of muscle disuse may mitigate the resulting decline in muscle protein synthesis (MPS). The purpose of this randomized pilot study was to determine the effect of increased protein intake during periods of disuse before anterior cruciate ligament (ACL) reconstruction on myofibrillar protein synthesis (MyoPS), and proteolytic and myogenic gene expression. Six healthy, young males (30 ± 9 y) were randomized to consume a high-quality, optimal protein diet (OP; 1.9 g·kg−1·d−1) or adequate protein diet (AP; 1.2 g·kg−1·d−1) for two weeks before ACL reconstruction. Muscle biopsies collected during surgery were used to measure integrated MyoPS during the intervention (via daily deuterium oxide ingestion) and gene expression at the time of surgery. MyoPS tended to be higher, with a large effect size in OP compared to AP (0.71 ± 0.1 and 0.54 ± 0.1%·d−1; p = 0.076; g = 1.56). Markers of proteolysis and myogenesis were not different between groups (p > 0.05); however, participants with greater MyoPS exhibited lower levels of MuRF1 gene expression compared to those with lower MyoPS (r = −0.82, p = 0.047). The data from this pilot study reveal a potential stimulatory effect of increased daily protein intake on MyoPS during injury-mediated disuse conditions that warrants further investigation.

NKT cells prevent chronic joint inflammation after infection with Borrelia burgdorferi.

Borrelia burgdorferi is the etiologic agent of Lyme disease, a multisystem inflammatory disorder that principally targets the skin, joints, heart, and nervous system. The role of T lymphocytes in the development of chronic inflammation resulting from B. burgdorferi infection has been controversial. We previously showed that natural killer T (NKT) cells with an invariant (i) TCR alpha chain (iNKT cells) recognize glycolipids from B. burgdorferi, but did not establish an in vivo role for iNKT cells in Lyme disease pathogenesis. Here, we evaluate the importance of iNKT cells for host defense against these pathogenic spirochetes by using Valpha14i NKT cell-deficient (Jalpha18(-/-)) BALB/c mice. On tick inoculation with B. burgdorferi, Jalpha18(-/-) mice exhibited more severe and prolonged arthritis as well as a reduced ability to clear spirochetes from infected tissues. Valpha14i NKT cell deficiency also resulted in increased production of antibodies directed against both B. burgdorferi protein antigens and borrelial diacylglycerols; the latter finding demonstrates that anti-glycolipid antibody production does not require cognate help from Valpha14i NKT cells. Valpha14i NKT cells in infected wild-type mice expressed surface activation markers and produced IFNgamma in vivo after infection, suggesting a participatory role for this unique population in cellular immunity. Our data are consistent with the hypothesis that the antigen-specific activation of Valpha14i NKT cells is important for the prevention of persistent joint inflammation and spirochete clearance, and they counter the long-standing notion that humoral rather than cellular immunity is sufficient to facilitate Lyme disease resolution.

Preoperative stress conditioning prevents paralysis after experimental aortic surgery: increased heat shock protein content is associated with ischemic tolerance of the spinal cord.

BACKGROUND: All forms of surgical therapy are stressful and injurious. The problems of paralysis, renal dysfunction, and colonic ischemia associated with aortic occlusion are due to acute ischemia-reperfusion injury at the cellular level. Acute-anterior spinal cord ischemia is the most devastating outcome of these iatrogenic-ischemic events. The majority of surgical procedures are performed electively and therefore provide an opportunity to preoperatively condition the patient to minimize these ischemia-related morbidities. OBJECTIVES: We sought to determine whether acute spinal cord injury associated with aortic occlusion can be prevented by induction of the cellular stress response by means of preoperative administration of whole-body hyperthermia or stannous chloride. METHODS: The study consisted of an experimental rabbit model of infrarenal aortic occlusion for 20 minutes at normothermic body temperature. RESULTS: Control rabbits experienced an 88% (7/8) incidence of paralysis after spinal cord ischemia induced by 20 minutes of aortic occlusion, whereas animals treated preoperatively with either whole-body hyperthermia (0/9) or stannous chloride (0/4) never became paralyzed (P <.001 for control vs treated groups). Ischemic protection of the spinal cord was associated with increased content of stress proteins within tissues of pretreated animals. CONCLUSION: Prior induction of the heat shock response in the whole animal will increase the content of stress proteins within the spinal cord and other tissues and result in the prevention of hind-limb paralysis associated with aortic occlusion. We have designated the preoperative induction of the cellular stress response for the prevention of ischemic tissue injury stress conditioning. We suggest that stress-conditioning protocols represent the opportunity to practice preventative medicine at the molecular level.

CD8alphaalpha-mediated survival and differentiation of CD8 memory T cell precursors.

Memory T cells are long-lived antigen-experienced T cells that are generally accepted to be direct descendants of proliferating primary effector cells. However, the factors that permit selective survival of these T cells are not well established. We show that homodimeric alpha chains of the CD8 molecule (CD8alphaalpha) are transiently induced on a selected subset of CD8alphabeta+ T cells upon antigenic stimulation. These CD8alphaalpha molecules promote the survival and differentiation of activated lymphocytes into memory CD8 T cells. Thus, memory precursors can be identified among primary effector cells and are selected for survival and differentiation by CD8alphaalpha.