Characterization of persistent poliovirus mutants selected in human neuroblastoma cells

Six Sabin-derived persistent poliovirus mutants were selected in human neuroblastoma IMR-32 cells. The mutants had a titer 30 to 10⁵ times lower in nonneural HEp-2c cells than in IMR-32 cells. When the growth cycles of persistent viruses in the two cell lines were compared, the most striking feature was a delay of 2 to 4 hr in virus release from HEp-2c cells. In HEp-2c cells, type 1 mutants could spontaneously establish a persistent infection in the absence of any exogenous viral inhibitor. Mutations at a rate of 1 every 210 nucleotides had accumulated in the genome of the type 1 mutants selected in neuroblastoma cells, modifying cell specificity and conferring the ability to persist in some non-neural cells. These results indicate that mutants of poliovirus with highly modified biological properties can be selected in vitro in cells of neural origin.     

Detection of hepatitis A virus proteins in infected BS-C-1 cells.

Hepatitis A virus (HAV) is distinguished from other picornaviruses by its tropism for the liver in infected hosts, a nonlytic infection in hepatocytes, and a slow and nonlytic growth cycle in cultured cells. Although the genome structure and organization of HAV appear to be similar to those of the other picornaviruses, the viral proteins synthesized in infected cells have not been previously characterized. We have utilized specific antisera raised in rabbits to recombinant HAV proteins expressed in Escherichia coli in an effort to identify both structural and nonstructural proteins in BS-C-1 cells throughout the course of a viral replication cycle. Replication was monitored by dot blot hybridization of viral genomes. Structural proteins VP0, VP1, VP2, and VP3 were found to accumulate during the infection cycle as did viral RNA. Nonstructural proteins 2C and 3D were not detected on immunoblots, although a minor amount of 2C could be detected by immunoprecipitation of lysates of radiolabeled, infected cells. The relative sensitivities of the various antisera were determined, and the failure to observe nonstructural proteins was shown not to be due to decreased sensitivity of the detection reagents. Thus, it appears that HAV nonstructural proteins do not accumulate in infected cells to levels comparable to those of capsid proteins.     

The effect of poliovirus infection on the translation in vitro of VSV messenger ribonucleoprotein particles

Messenger ribonucleoprotein (mRNP) particles were isolated and examined for the presence of factors involved in the inhibition of protein synthesis induced by poliovirus infection. Vesicular stomatitis virus (VSV) mRNPs were used as a model for cellular mRNPs. These mRNPs were translated in HeLa cell extracts with a similar efficiency and optimal conditions to that of purified mRNA, but they were not translated in extracts prepared from poliovirus-infected HeLa cells, which have been shown to be defective in cap-binding protein activity. We conclude that mRNP proteins do not include cap-binding protein activity, since the mRNPs were not able to bypass the restriction on translation of capped mRNAs in polio-infected cell extracts. In addition, VSV mRNPs were isolated from polio-superinfected cells, in which their translation was inhibited. These mRNPs were translated in vitro as well as normal VSV mRNPs. No evidence of a modification or a blocking factor on the mRNPs which prevented their translation following polio infection was observed. Thus, within the limits of the in vitro translation assays used, no factors involved in the discrimination between polioviral and cellular or VSV mRNA could be detected in the mRNP particle.     

Mitochondria-rich cells of frog skin in transport mechanisms: morphological and kinetic studies on transepithelial excretion of methylene blue.

The following study combines histological observations on the localization and density of mitochondria-rich cells with a kinetic study of the part played by these cells in transport phenomena. In the ventral skin, mitochondria-rich cells and granular cells are equally abundant in the first living cell layer. The mitochondria-rich cells were shown to excrete methylene blue [3,9-bis-(dimethylamino)-phenozathionum chloride]. A kinetic study of this excretion across the isolated epithelium of Rana esculenta skin showed that the mechanism of the excretion was a saturable one. An important fraction of methylene blue excretion depends on the absorption of sodium; the absence of this ion, or the inhibition of its transport by ouabain or amiloride, inhibits the excretion of the organic base. The mitochondria-rich cells, however, do not appear to play a determining role in sodium transport.     

Aortic aneurysm and dissection are not associated with an increased risk for giant cell arteritis/ polymyalgia rheumatica

It has recently been claimed that giant cell arteritis (GCA) is associated with a markedly increased risk of aortic aneurysm formation or rupture. In the present study, the opposite approach was taken, by looking for the incidence of GCA and polymyalgia rheumatica (PMR) in patients with aortic aneurysm, aortic dissection, or both (AA/D). The records of 315 consecutive patients admitted with the diagnosis of AA/D were reviewed. In addition, follow up information was obtained in 82 patients by examination in the outpatient clinic. After careful examination and assessment of clinical and laboratory data, it was found that none of the 82 patients who survived hospitalisation and were available for examination had GCA or PMR. Moreover, review of the retrospective data available from hospital records of the total consecutive 315 patients with AA/D failed to find any patient with a diagnosis of GCA/PMR. In conclusion, the present study did not find an increased prevalence of GCA/PMR among a cohort of Israeli patients with AA/D. Therefore, it is suggested that a thorough investigation aiming to diagnose GCA/PMR is not cost effective in most of the elderly patients presenting with AA/D.