Antibody avidity measurement and immune complex dissociation for serological diagnosis of vertically acquired HIV-1 infection.

Differences in avidity between HIV-1 antibodies transmitted passively and antibodies synthesized by children born to HIV-1-positive mothers can be measured using a commercially available competitive enzyme immunoassay kit. The avidity determination method is based on the competition between an anti-HIV-1-peroxidase-labeled antibody at a stable and known concentration and the anti-HIV-1 antibodies (IgA, IgG, IgM) present in the child's serum at various and increasing dilutions. The shift in the competition/dilution curves between serum samples taken at the third and the sixth month of the child's life showed either the loss or the synthesis of anti-HIV-1 antibodies. The antibody avidity determination combined with a test detecting free or complexed p24 antigen is a workable and inexpensive serological method for the follow-up of children born to seropositive mothers. Combining these two complementary methods, HIV-1 infection has been established at 6 months of age in 13 of 13 infants, and positive results were confirmed by coculture and by PCR. An HIV-1 infection was excluded at 6 months of age in 17 of 17 infants, results otherwise confirmed by virological and clinical follow-up. These new and convenient approaches to the diagnosis of vertically acquired HIV-1 could be used worldwide, including in developing countries.

Influence of alpha- and beta-adrenoceptors on thrombin-induced serotonin release in rat platelets.

This work was designed to investigate the influence of rat platelet adrenoceptors on the early thrombin-induced serotonin release. In washed platelets prelabeled with [3H]-serotonin, adrenaline and isoproterenol both inhibited, in a dose-dependent manner, the early thrombin-induced secretion of serotonin. Inhibitory responses of both adrenaline and isoproterenol were blocked in the presence of beta-adrenoceptor antagonists, suggesting that the catecholamine acted solely through beta-adrenoceptors. However, isoproterenol inhibited the thrombin-induced serotonin release to a much greater extent than the catecholamine, suggesting that the alpha 2-component of adrenaline might account for the difference observed between the two compounds. Our observation that selective alpha 2-adrenoceptor antagonists as yohimbine and rauwolscine potentiated the inhibitory effect of adrenaline to a level close to that observed with isoproterenol, lends support to the above hypothesis. This latter result suggested that, conversely, alpha 2-adrenergic compounds might exert a counteracting effect on a full beta-adrenoceptor mediated inhibition. Although synthetic alpha 2-adrenergic agents failed to influence isoproterenol inhibitory effect, our study shows that prestimulation of beta-adrenoceptors by isoproterenol, followed by addition of adrenaline or noradrenaline markedly diminished the inhibitory effect of isoproterenol to a level close to that which characterized the inhibition observed with catecholamines, when tested alone. Our work favours the hypothesis that, in rat platelets, early after platelet stimulation, catecholamines might counteract a beta-adrenoceptor- mediated inhibition, through alpha 2-adrenoceptor sites.

Influence of adrenoceptors on thrombin-induced phosphoinositide metabolism in rat platelets.

Stimulation of washed rat platelets with thrombin resulted in an increased turnover of phosphoinositides. Adrenaline and isoproterenol both inhibited thrombin-induced phosphatidic acid formation in a dose-dependent manner. Inhibitory responses of both compounds were blocked by a beta-adrenoceptor antagonist. However, isoproterenol was a more potent inhibitor than adrenaline. Addition of a selective alpha2-adrenoceptor antagonist potentiated the inhibitory effect of adrenaline up to the level observed with isoproterenol. Prestimulation of beta-adrenoceptors with isoproterenol, followed by addition of adrenaline (or noradrenaline) markedly diminished the inhibitory effect induced by the full beta-adrenoceptor agonist. Our results indicate that, in rat platelets, catecholamines are able to counteract, via alpha2-receptors, the beta-adrenoceptor-mediated inhibition of thrombin-induced phosphatidic acid formation. This suggests that catecholamines, by controlling cAMP level, may modulate phospholipase C activity and thereby platelet reactivity.