In this report, we present evidence that R5 human immunodeficiency virus type 1 (HIV-1) replicates more efficiently in primary CD4؉ T cells than X4 HIV-1. By comparing CD3/CD28-costimulated CD4 ؉ T-cell cultures infected by several X4 and R5 HIV-1 strains, we determined that R5-infected CD4 ؉ T cells produce more virus over time than X4-infected CD4 ؉ T cells. In the first comparison, we found that more cells were infected by the X4-tropic strain LAI than by the R5-tropic strain JR-CSF and yet that higher levels of viral production were detected in the R5-infected cultures. The differential viral production was partially due to the severe cytopathic effects of the X4 virus. We also compared cultures infected with the isogenic HIV-1 strains NL4-3 (X4) and 49.5 (R5). We found that fewer cells were infected by the R5 strain, and yet similar levels of viral production were detected in both infected cultures. Cell death played less of a role in the differential viral production of these strains, as the cell viability remained comparable in both X4-and R5-infected cultures over time. The final comparison involved the primary R5-tropic isolate KP1 and the primary dual-tropic isolate KP2. Although both strains infected similar numbers of cells and induced comparable levels of cytopathicity, viral production was considerably higher in the R5-infected culture. In summary, these data demonstrate that R5 HIV-1 has an increased capacity to replicate in costimulated CD4؉ T cells compared to X4 HIV-1.Human immunodeficiency virus type 1 (HIV-1) infects cells by binding to the CD4 receptor and to one of several coreceptors expressed on the surface of target cells (2,13,15,16,18,26). The chemokine receptors CCR5 and CXCR4 serve as the major coreceptors for HIV-1, although several other chemokine receptors have been linked to minor HIV-1 coreceptor usage (2,8,15,18,32,52). Characteristically, non-syncytiuminducing (NSI) isolates utilize CCR5 as a coreceptor and are referred to as R5 strains (2, 14-16). R5 strains often represent the dominant viral population detected during the early stages of clinical HIV-1 infection (9,14,41,43,46,53). In contrast, syncytium-inducing (SI) isolates utilize CXCR4 as a coreceptor and are referred to as X4 strains (18,20,24,25,28,30,40,45,48). X4 strains are typically detected in the later stages of infection and are associated with rapid CD4 ϩ T-cell loss (11,14,24,25,46,48,49). Despite the link between X4 emergence and disease progression, approximately half of all individuals with AIDS continue to harbor predominantly R5 viruses, suggesting that CXCR4 coreceptor usage alone is not responsible for disease progression (9,43,46,53).Several mechanisms have been proposed to explain the R5 dominance of early HIV-1 infection. There is evidence that R5 strains may be transmitted at an increased frequency compared to X4 strains. For example, individuals that carry a 32-bp deletion mutation (⌬32) in the CCR5 gene are highly resistant to HIV-1 infection (10,33,38,44). Although these individuals are suscepti...
Predator-prey interactions can be influenced by the behaviour of individual species as well as environmental factors. We conducted laboratory experiments to test for the influences of two abiotic factors (light intensity and habitat complexity) on predator-prey interactions between walleye Sander vitreus and two prey species, bluegill Lepomis macrochirus and golden shiner Notemigonus crysoleucas. Three light intensities were simulated (day, twilight and night) in the presence or absence of simulated vegetation. Observations of predator behaviour indicated that walleye increased activity and foraging success with decreasing light levels and had most success capturing dispersed, closer prey. While schooling could not be maintained as light levels diminished, prey decreased predation vulnerability by moving into vegetation or higher in the water column. Throughout all treatments, bluegill were more evasive to capture as the number of strikes was similar on both prey but capture rates were higher for golden shiner. Although light intensity and simulated habitat complexity affected predator and prey behaviour, these factors did not interact to influence foraging success of walleye. To fully understand predator and prey behaviours in fishes, an understanding of species-specific responses to abiotic and biotic factors is necessary.
Markers of maturation and activation were measured on peripheral CD4+ T cells in chronically HIV-1-infected patients in a randomized, controlled pilot study of structured treatment interruption (STI). Eight subjects underwent 2 cycles of 1 month off and 1 month on highly active antiretroviral therapy (HAART), followed by a final 3-month interruption. During STI, CD4+ T-cell percentage remained relatively stable in 4 of 8 subjects. The remaining 4 STI subjects had significant rapid decline in CD4+ T-cell percentage during STI, followed by return to pre-STI baseline while on HAART. Changes in overall CD4+ T-cell percentage corresponded with fluctuations in the CD45RA+CCR7+ naive and CD45RA-CCR7+ central memory subsets. Subjects with variable CD4+ T-cell percentages tended to have higher pre-HAART plasma HIV-1 RNA set-points and experienced higher levels of plasma HIV-1 RNA rebound during STI. These results suggest that interruptions should be avoided whenever possible in patients on HAART with high plasma HIV-1 RNA set-points.
Ultrafast laser processing applications need fast approaches to assess the nonlinear propagation of the laser beam in order to predict the optimal range of processing parameters in a wide variety of cases. We develop here a method based on the simple monitoring of the nonlinear beam shaping against numerical prediction. The numerical code solves the nonlinear Schrödinger equation with nonlinear absorption under simplified conditions by employing a state-of-the art computationally efficient approach. By comparing with experimental results we can rapidly estimate the nonlinear refractive index and nonlinear absorption coefficients of the material. The validity of this approach has been tested in a variety of experiments where nonlinearities play a key role, like spatial soliton shaping or fs-laser waveguide writing. The approach provides excellent results for propagated power densities for which free carrier generation effects can be neglected. Above such a threshold, the peculiarities of the nonlinear propagation of elliptical beams enable acquiring an instantaneous picture of the deposition of energy inside the material realistic enough to estimate the effective nonlinear refractive index and nonlinear absorption coefficients that can be used for predicting the spatial distribution of energy deposition inside the material and controlling the beam in the writing process.
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