Aggregation of influenza virus ribonucleocapsids at low pH.

Uncoating of influenza occurs in endosomes where the acid environment is instrumental in membrane fusion and the dissociation of the ribonucleoprotein (RNP) from matrix protein by the action of the hemagglutinin and M2 protein ion channels, respectively. Earlier studies have shown that low pH treatment results in the release of M1 protein from RNP. To obtain RNP free of M1 protein, we attempted to isolate RNP by velocity sedimentation on pH 5 glycerol gradients; however, the RNP sedimented as pellets under centrifugation conditions that had previously resolved RNP on neutral gradients. The increase in sedimentation rate occurred between pH 5.6 and 6.0 and was reversible for a portion of the RNP on raising the pH to neutrality. RNP isolated from infected cells or virions sedimented on acidification and was seen to form clumps visible by electron microscopy. If acidification preceded NP40 detergent lysis, virion RNP appeared to be released as genomic complexes. The pH threshold for viral membrane fusion was 5.8 indicating that the same pH condition also resulted in aggregation of RNP. Because exposure of virions to pH 5 occurs during uncoating in endosomes and is essential for infectivity, it is possible that low pH-induced RNP aggregation may facilitate aspects of viral uncoating such as dissociation of RNP from M1 or transport of genomes to the nucleus.

Nomogram for predicting the likelihood of delayed graft function in adult cadaveric renal transplant recipients.

Delayed graft function (DGF) is the need for dialysis in the first week after transplantation. Studied were risk factors for DGF in adult (age >/=16 yr) cadaveric renal transplant recipients by means of a multivariable modeling procedure. Only donor and recipient factors known before transplantation were chosen so that the probabilities of DGF could be calculated before transplantation and appropriate preventative measures taken. Data on 19,706 recipients of cadaveric allografts were obtained from the United States Renal Data System registry (1995 to 1998). Graft losses within the first 24 h after surgery were excluded from the analysis (n = 89). Patients whose DGF information was missing or unknown (n = 2820) and patients missing one or more candidate predictors (n = 2951) were also excluded. By means of a multivariable logistic regression analysis, factors contributing to DGF in the remaining 13,846 patients were identified. After validating the logistic regression model, a nomogram was developed as a tool for identifying patients at risk for DGF. The incidence of DGF was 23.7%. Sixteen independent donor or recipient risk factors were found to predict DGF. A nomogram quantifying the relative contribution of each risk factor was created. This index can be used to calculate the risk of DGF for an individual by adding the points associated with each risk factor. The nomogram provides a useful tool for developing a pretransplantation index of the likelihood of DGF occurrence. With this index in hand, better informed treatment and allocation decisions can be made.