Publications

Genotyping frequently is used to distinguish recrudescent from new infections in antimalarial drug efficacy trials, but methodology and interpretation of results have not been standardized. We compared the utility of polymorphisms within 3 Plasmodium falciparum genes during a longitudinal trial in Kampala, Uganda. Merozoite surface protein-1 (msp-1) and merozoite surface protein-2 (msp-2) revealed greater diversity than glutamate-rich protein. Genotypes based on msp-1, msp-2, and all 3 genes combined were compared for 394 initial and subsequent isolates. Classification of most episodes as due to recrudescence or reinfection was straightforward. In 24% (msp-1), 16% (msp-2), and 62% (3 genes combined) of samples, subsequent episodes contained identical and new alleles, however. Our analysis suggested that such episodes should be classified as reinfections and not recrudescence. Comparing the 3 studied genes, msp-2 results were most accurate, and analysis of this single gene effectively distinguished recrudescence from reinfection in our study population.

Vagal afferent activity modulates mechanical nociceptive threshold and inflammatory mediator-induced hyperalgesia, effects that are mediated by the adrenal medulla. To evaluate the role of epinephrine, the major hormone released from the adrenal medulla, the beta2-adrenergic receptor antagonist ICI 118,551 was chronically administered to vagotomized rats and epinephrine to normal rats. In vagotomized rats, chronic administration of ICI 118,551 markedly attenuated vagotomy-induced enhancement of bradykinin hyperalgesia but had no effect on nociceptive threshold. In normal rats, chronic epinephrine had the opposite effect, enhancing bradykinin hyperalgesia. Like vagotomy-, epinephrine-induced enhancement of hyperalgesia developed slowly, taking 14 days to reach its peak. Vagotomy induced a chronic elevation in plasma concentrations of epinephrine. We suggest that ongoing activity in vagal afferents inhibits the release of epinephrine from the adrenal medulla. Chronically elevated levels of epinephrine, occurring after vagotomy, desensitize peripheral beta2-adrenergic receptors and lead to enhancement of bradykinin hyperalgesia. The ability of prolonged elevated plasma levels of epinephrine to sensitize bradykinin receptors could contribute to chronic generalized pain syndromes.

The mechanism by which chronic stress affects the course of inflammatory diseases is still not well understood. We have evaluated the effect of two types of nonhabituating stress on a major component of the inflammatory response, synovial plasma extravasation, induced by perfusion of the potent inflammatory mediator, bradykinin and evaluated the underlying neuroendocrine mechanism in the rat. Chronic intermittent noise or ether stress induced profound inhibition of bradykinin-induced plasma extravasation, which is associated with increased adjuvant-arthritis severity. This inhibition, however, took 24 h to fully develop after the last exposure to stress and persisted for at least 48 h. The inhibition could be reversed by an additional exposure to the stressor, just prior to measuring the inflammatory response, suggesting that the delay is due to stress-induced release of a factor that acutely masks the inhibition of the inflammatory response. This novel, unexpected feature of the effect of nonhabituating stress on inflammation may help explain variability in effects of stress in patients with inflammatory disease. The effect of nonhabituating stress on inflammation was dependent on the sympathoadrenal axis with no detectable contribution by the hypothalamic-pituitary-adrenal axis.

The nef gene products encoded by human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus type 1 (SIV-1) increase viral loads in infected hosts and accelerate clinical progression to AIDS. Nef exhibits a spectrum of biological activities, including the ability to downregulate surface expression of CD4 and major histocompatibility complex (MHC) class I antigens, to alter the state of T-cell activation, and to enhance the infectivity of viral particles. To determine which of these in vitro functions most closely correlates with the pathogenic effects of Nef in vivo, we constructed recombinant HIV-1 NL4-3 viruses carrying mutations within the nef gene that selectively impair these functions. These mutant viruses were evaluated for pathogenic potential in severe combined immunodeficiency (SCID) mice implanted with human fetal thymus and liver (SCID-hu Thy/Liv mice), in which virus-mediated depletion of thymocytes is known to be Nef dependent. Disruption of the polyproline type II helix (Pxx)4 within Nef (required for binding of Hck and p21-activated kinase-like kinases, downregulation of MHC class I, and enhancement of HIV-1 infectivity in vitro but dispensable for CD4 downregulation) did not impair thymocyte depletion in virus-infected Thy/Liv human thymus implants. Conversely, three separate point mutations in Nef that compromised its ability to downregulate CD4 attenuated thymocyte depletion while not diminishing viral replication. These findings indicate that the functional ability of Nef to downregulate CD4 and not MHC class I downregulation, Hck or PAK binding, or (Pxx)4-associated enhancement of infectivity most closely correlates with Nef-mediated enhancement of HIV-1 pathogenicity in vivo. Nef-mediated CD4 downregulation merits consideration as a new target for the development of small-molecule inhibitors.

We review two new HIV counseling and testing guidelines by the U.S. Centers for Disease Control and Prevention. The guidelines, which address the general population and pregnant women, reflect an important shift in the goals and methods of counseling and testing that has widespread implications. The guidelines' defining characteristic is the greater emphasis on increasing the numbers of people knowing their HIV status while maintaining the historical focus on extensive pretest counseling and consent procedures. We discuss the policy and practice implications by evaluating five factors: 1) Will the guidelines be adopted? 2) Will at-risk and infected individuals be identified for counseling and testing? 3) Will health care providers offer counseling and testing and patients accept counseling and testing, obtain their test results, seek treatment, and change risky behaviors? 4) Will the guidelines be relatively cost-effective? 5) Will the guidelines be compatible with ethical standards?

Tidal volume reduction during mechanical ventilation reduces mortality in patients with acute lung injury and the acute respiratory distress syndrome. To determine the mechanisms underlying the protective effect of low tidal volume ventilation, we studied the time course and reversibility of ventilator-induced changes in permeability and distal air space edema fluid clearance in a rat model of ventilator-induced lung injury. Anesthetized rats were ventilated with a high tidal volume (30 ml/kg) or with a high tidal volume followed by ventilation with a low tidal volume of 6 ml/kg. Endothelial and epithelial protein permeability were significantly increased after high tidal volume ventilation but returned to baseline levels when tidal volume was reduced. The basal distal air space fluid clearance (AFC) rate decreased by 43% (P < 0.05) after 1 h of high tidal volume but returned to the preventilation rate 2 h after tidal volume was reduced. Not all of the effects of high tidal volume ventilation were reversible. The cAMP-dependent AFC rate after 1 h of 30 ml/kg ventilation was significantly reduced and was not restored when tidal volume was reduced. High tidal volume ventilation also increased lung inducible nitric oxide synthase (NOS2) expression and air space total nitrite at 3 h. Inhibition of NOS2 activity preserved cAMP-dependent AFC. Because air space edema fluid inactivates surfactant and reduces ventilated lung volume, the reduction of cAMP-dependent AFC by reactive nitrogen species may be an important mechanism of clinical ventilator-associated lung injury.