Constitutive CD8 expression allows inefficient maturation of CD4+ helper T cells in class II major histocompatibility complex mutant mice.

Although mature CD4+ T cells bear T cell receptors (TCRs) that recognize class II major histocompatibility complex (MHC) and mature CD8+ T cells bear TCRs that recognize class I MHC, it is possible that the initial commitment of an immature thymocyte to a CD4 or CD8 lineage is made without regard to the specificity of the TCR. According to this model, CD4+ cells with class I TCR do not mature because the CD8 coreceptor is required for class I MHC recognition and positive selection. If this model is correct, constitutive expression of CD8 should allow CD4+ T cells with class I-specific TCRs to develop. In this report, we show that mature peripheral CD4+ cells are present in class II MHC-deficient mice that express a constitutive CD8.1 transgene. These cells share a number of properties with the major class II MHC-selected CD4 population, including the ability to express CD40 ligand upon activation. Although mature CD4 cells are also detectable in the thymus of class II MHC mutant/CD8.1 transgenic mice, they represent a small fraction of the mature CD4 cells found in mice that express class II MHC. These results indicate that some T cells choose the CD4 helper lineage independent of their antigen receptor specificity; however, the inefficiency of generating class I-specific CD4 cells leaves open the possibility that an instructive signal generated upon MHC recognition may bias lineage commitment

Mice Infected with Low-virulence Strains of Toxoplasma gondii Lose their Innate Aversion to Cat Urine, Even after Extensive Parasite Clearance

Toxoplasma gondii chronic infection in rodent secondary hosts has been reported to lead to a loss of innate, hard-wired fear toward cats, its primary host. However the generality of this response across T. gondii strains and the underlying mechanism for this pathogen mediated behavioral change remain unknown. To begin exploring these questions, we evaluated the effects of infection with two previously uninvestigated isolates from the three major North American clonal lineages of T. gondii, Type III and an attenuated strain of Type I. Using an hour-long open field activity assay optimized for this purpose, we measured mouse aversion toward predator and non-predator urines. We show that loss of innate aversion of cat urine is a general trait caused by infection with any of the three major clonal lineages of parasite. Surprisingly, we found that infection with the attenuated Type I parasite results in sustained loss of aversion at times post infection when neither parasite nor ongoing brain inflammation were detectable. This suggests that T. gondii-mediated interruption of mouse innate aversion toward cat urine may occur during early acute infection in a permanent manner, not requiring persistence of parasitecysts or continuing brain inflammation.Comment: 14 pages, 3 figure

REACTIVE STRENGTH INDEX-MODIFIED IN DIFFERENT PLYOMETRIC TASKS

The Reactive Strength Index-Modified (RSl,d) is a reliable method of measuring the explosiveness of an athlete during a range of plyometric exercises. The purpose of the current study was to measure the between-limb differences in RSlmod across three different plyometric tasks. Eleven recreationally active participants performed countermovement jumps, stop jumps and single-leg jumps. The study found no significant differences in RSlmod between dominant and non-dominant limbs across all three tasks (p>0.05), but did find RSI,d to be higher in the stop jump than a countermovement jump and single leg stop jump for both dominant and non-dominant limbs. These findings show RSlmod may not be an indicator of limb asymmetry, but may be useful for the coach when looking to develop ex@losive performance in an athlete or performer

From stem cells to bone-forming cells

Bone formation starts near the end of the embryonic stage of development and continues throughout life during bone modeling and growth, remodeling, and when needed, regeneration. Bone-forming cells, traditionally termed osteoblasts, produce, assemble, and control the mineralization of the type I collagen-enriched bone matrix while participating in the regulation of other cell processes, such as osteoclastogenesis, and metabolic activities, such as phosphate homeostasis. Osteoblasts are generated by different cohorts of skeletal stem cells that arise from different embryonic specifications, which operate in the pre-natal and/or adult skeleton under the control of multiple regulators. In this review, we briefly define the cellular identity and function of osteoblasts and discuss the main populations of osteoprogenitor cells identified to date. We also provide examples of long-known and recently recognized regulatory pathways and mechanisms involved in the specification of the osteogenic lineage, as assessed by studies on mice models and human genetic skeletal diseases

REACTIVE STRENGTH INDEX-MODIFIED IN DIFFERENT PLYOMETRIC TASKS

The Reactive Strength Index-Modified (RSlmod) is a reliable method of measuring the explosiveness of an athlete during a range of plyometric exercises. The purpose of the current study was to measure the between-limb differences in RSlmod across three different plyometric tasks. Eleven recreationally active participants performed countermovement jumps, stop jumps and single-leg jumps. The study found no significant differences in RSlmod between dominant and non-dominant limbs across all three tasks (p\u3e0.05), but did find RSI,d to be higher in the stop jump than a countermovement jump and single leg stop jump for both dominant and non-dominant limbs. These findings show RSlmod may not be an indicator of limb asymmetry, but may be useful for the coach when looking to develop exPlosive performance in an athlete or performer

Towards the Promotion of Positive Development among Boys in Challenging Contexts: A Mixed-Methods Study of Engagement in the Scoutreach Initiative

Engagement in youth development programs reflects the quality of young people’s program-related experiences. However, more research is needed that explores cognitive, emotional, and behavioral dimensions of engagement in programs that serve underrepresented youth of color. The present cross-sectional and mixed-methods study assessed potential relations among dimensions of engagement in the Boston-area Scoutreach initiative, character attributes, self-perceived school competence, and intentional self-regulation. We analyzed data from 32 Scouts (Mage = 9.97 years, SD = 2.46, Range = 6 to 14), 32 parents/guardians, and five Scoutreach leaders. Scouts demonstrated that they were cognitively, emotionally, and behaviorally engaged in Scoutreach, and these dimensions were related differentially to indicators of healthy development. Qualitative data elucidated key aspects of Scoutreach (e.g., camping, peer relationships) that were linked to youth engagement. We discuss limitations of the present study and implications for future research and practice

Toxoplasma gondii‐infected natural killer cells display a hypermotility phenotype in vivo

Toxoplasma gondii is a highly prevalent intracellular protozoan parasite that causes severe disease in congenitally infected or immunocompromised hosts. T. gondii is capable of invading immune cells and it has been suggested that the parasite harnesses the migratory pathways of these cells to spread through the body. Although in vitro evidence suggests that the parasite further enhances its spread by inducing a hypermotility phenotype in parasitized immune cells, in vivo evidence for this phenomenon is scarce. Here we use a physiologically relevant oral model of T. gondii infection, in conjunction with two‐photon laser scanning microscopy, to address this issue. We found that a small proportion of natural killer (NK) cells in mesenteric lymph nodes contained parasites. Compared with uninfected ‘bystander’ NK cells, these infected NK cells showed faster, more directed and more persistent migratory behavior. Consistent with this, infected NK cells showed impaired spreading and clustering of the integrin, LFA‐1, when exposed to plated ligands. Our results provide the first evidence for a hypermigratory phenotype in T. gondii‐infected NK cells in vivo, providing an anatomical context for understanding how the parasite manipulates immune cell motility to spread through the host