White blood cells (WBCs) were counted in 4697 individuals who presented to outpatient malaria clinics in Maesod, Tak Province, Thailand, and Iquitos, Peru, between 28 May and 28 August 1998 and between 17 May and 9 July 1999. At each site and in each year, WBC counts in the Plasmodium falciparum-infected patients were lower than those in the Plasmodium vivax-infected patients, which, in turn, were lower than those in the uninfected patients. In Thailand, one-sixth of the P. falciparum-infected patients had WBC counts of <4000 cells/microL. Leukopenia may confound population studies that estimate parasite densities on the basis of an assumed WBC count of 8000 cells/microL. For instance, in the present study, use of this conventional approach would have overestimated average asexual parasite densities in the P. falciparum-infected patients in Thailand by nearly one-third.

A number of extracellular stimuli, including soluble cytokines and insoluble matrix factors, are known to influence murine embryonic stem cell self-renewal and differentiation behavioral responses via intracellular signaling pathways, but their net effects in combination are difficult to understand. To gain insight concerning key intracellular signals governing these behavioral responses, we employ a multivariate systems analysis of proteomic data generated from combinatorial stimulation of mouse embryonic stem cells by fibronectin, laminin, leukemia-inhibitory factor, and fibroblast growth factor 4. Phosphorylation states of 31 intracellular signaling network components were obtained across 16 different stimulus conditions at three time points by quantitative Western blotting, and partial-least-squares modeling was used to determine which components were most strongly correlated with cell proliferation and differentiation rate constants obtained from flow cytometry measurements of Oct-4 expression levels. This datadriven, multivariate (16 conditions ؋ 31 components ؋ 3 time points ‫؍‬ Ϸ1,500 values) proteomic approach identified a set of signaling network components most critically associated (positively or negatively) with differentiation (Stat3, Raf1, MEK, and ERK), proliferation of undifferentiated cells (MEK and ERK), and proliferation of differentiated cells (PKB␣, Stat3, Src, and PKC). These predictions were found to be consistent with previous in vivo literature, along with direct in vitro test here by a peptide inhibitor of PKC. Our results demonstrate how a computational systems biology approach can elucidate key sets of intracellular signaling protein activities that combine to govern cell phenotypic responses to extracellular cues. Mouse embryonic stem (ES) cells are derived from the inner cell mass of preimplantation blastocysts (1). They are pluripotent and can contribute to every tissue in the adult organism (2). This developmental potential can be maintained in vitro in the presence of the gp130 signaling ligand, leukemiainhibitory factor (LIF) (3, 4). Binding of LIF to the LIFR-gp130 receptor complex stimulates signaling through two main pathways, the Janus kinase (JAK)͞signal transducers and activators of transcription (STAT) pathway and the mitogen-activated protein kinase kinase (MEK)͞extracellular-regulated kinase (ERK) pathway (5). The roles of these LIF-stimulated pathways in maintenance of ES cell pluripotency are not completely understood, although activation of Stat3 is indispensable for self-renewal (6, 7). Despite the importance of LIF in murine ES cell self renewal, maintenance of somatic stem cells in vitro has remained elusive, and ES cells from other species, e.g., human, apparently cannot be maintained by the presence of LIF alone (8, 9). Moreover, extracellular matrix factors, such as fibronectin (Fn) and laminin (Ln), can significantly influence the effects of cytokines (10-12).Cytokines and matrix factors that regulate ES cell processes operate through multiple intracellular s...