Natural Killer Cell Dependent Within-Host Competition Arises during Multiple MCMV Infection: Consequences for Viral Transmission and Evolution

It is becoming increasingly clear that many diseases are the result of infection from multiple genetically distinct strains of a pathogen. Such multi-strain infections have the capacity to alter both disease and pathogen dynamics. Infection with multiple strains of human cytomegalovirus (HCMV) is common and has been linked to enhanced disease. Suggestions that disease enhancement in multi-strain infected patients is due to complementation have been supported by trans-complementation studies in mice during co-infection of wild type and gene knockout strains of murine CMV (MCMV). Complementation between naturally circulating strains of CMV has, however, not been assessed. In addition, many models of multi-strain infection predict that co-infecting strains will compete with each other and that this competition may contribute to selective transmission of more virulent pathogen strains. To assess the outcome of multi-strain infection, C57BL/6 mice were infected with up to four naturally circulating strains of MCMV. In this study, profound within-host competition was observed between co-infecting strains of MCMV. This competition was MCMV strain specific and resulted in the complete exclusion of certain strains of MCMV from the salivary glands of multi-strain infected mice. Competition was dependent on Ly49H⁺ natural killer (NK) cells as well as the expression of the ligand for Ly49H, the MCMV encoded product, m157. Strains of MCMV which expressed an m157 gene product capable of ligating Ly49H were outcompeted by strains of MCMV expressing variant m157 genes. Importantly, within-host competition prevented the shedding of the less virulent strains of MCMV, those recognized by Ly49H, into the saliva of multi-strain infected mice. These data demonstrate that NK cells have the strain specific recognition capacity required to meditate within-host competition between strains of MCMV. Furthermore, this within-host competition has the capacity to shape the dynamics of viral shedding and potentially select for the transmission of more virulent virus strains.     

Investigation of vertical jump performance after completing heavy squat exercises

The purpose of this study was to determine whether vertical jump height was influenced by completing a half squat or quarter squat exercise prior to jumping. Ten male subjects experienced with the squat exercise performed 4 warm up squat sets followed by 1 repetition with the weight of 90% of 1 repetition maximum of the half squat or quarter squat. No difference in jump heights after any of the 3 conditions, including a control group (F = 3.096, p = 0.070), was found. Correlations between the relative strength ratio and the difference in averaged jump heights before and after the half and quarter squat conditions were also tested, and no correlation was found (r = -0.128, p = 0.724, and r = -0.189, p = 0.601, respectively). Although statistical significance at the 0.05 level was not observed for the comparison of jump heights between conditions, we did observe a trend (i.e., p = 0.07). Therefore, we examined the individual responses to the exercises and determined that 5 of the subjects did increase their vertical jumps after both squat exercises. It may be that the influence of prejump exercise on jump performance may be individualized. Nevertheless, the use of a strength ratio does not appear to predict who will benefit from posttetanic potentiation in this type of exercise situation.