Pathogenicity for suckling mice of Coxsackie viruses adapted to human amnion cells

Continuous passages in primary human amnion cell cultures of Coxsackie prototype viruses A-9, A-10, A-11, A-13, A-14, A-15, A-18, B-1, B-2, B-4, and B-5 increased the titers, hastened and enhanced cytopathic effect, and in varying degrees caused loss of virulence for newborn mice. Only B-3 behaved differently in that neither adaptation to cells in vitro nor attenuation with respect to the original animal host could be observed. Types A-15, B-1, B-2, and B-5 slowly regained virulence when passed in mice after high concentration passages in amnion cells whereas all other viruses reverted to their original virulence after only 1 or 2 passages in the animal host. When these strains, however, were purified by cloning procedures, they too showed markedly increased stability. In all stages of attenuation, viruses multiplied extensively in vivo as could be shown by titration in amnion cell cultures. It is suggested that a genetic mechanism is operative leading to virus populations in which the majority of the particles is qualitatively changed.

Sedimentation and autoradiographic analyses of rapidly labeled ribonucleic acids in human amnion cells

When human amnion cells were exposed to radioactive cytidine for 0.002 or 0.017 of one generation time, the alcohol-insoluble label in the RNA preparations from these cells was distributed between a rather homogeneous component of 4 to 8S and a fast mixture of 34S, 30S, 25S, 20S, and 15S. Evidence has been presented that these sedimenting components are RNA. More than 73 per cent of the label in the fast mixture from the cells labelled for 0.017 of one generation time was derived from the nuclei. The label in nucleotides after 0.017 of one generation time equaled 1.4 times that in RNA. Thus, the previous autoradiographic evidence for the nuclear origin of late cytoplasmic label is weak. The distribution of label among the various sedimenting components, as well as that between two pyrimidine nucleotide constitutents of 34S, 30S, 25S, and 15S components, changed when the length of exposure to radioactive cytidine was increased from 0.002 to 0.017 of one generation time. This result excluded the possibility that the population of the RNA labeled after 0.002 of one generation time was identical with that labeled later. This fact must be included in formulation of hypotheses for the function of rapidly labeled RNA's.

Loss of radioactivity from labeled DNA of primary human amnion cells

Primary human amnion cultures labeled with glycine-2-C(14) or thymidine-2-C(14) released more radioactivity into the media than could be accounted for by cell replacement. This is interpreted as degradation of acid-insoluble polydeoxynucleotides in a living human cell.

PROTEIN SYNTHESIS AND RNA SYNTHESIS DURING MITOSIS IN ANIMAL CELLS

Protein synthesis and RNA synthesis during mitosis were studied by autoradiography on mammalian tissue culture cells. Protein synthesis was followed by incubating hamster epithelial and human amnion cells for 10 or 15 minutes with phenylalanine-C(14). To study RNA synthesis the hamster cells were incubated for 10 minutes with uridine-C(14). Comparisons of the synthetic capacity of the interphase and mitotic cells were then made using whole cell grain counts. The rate of RNA synthesis decreased during prophase and reached a low of 13 to 16 per cent of the average interphase rate during metaphase-anaphase. Protein synthesis in the hamster cells showed a 42 per cent increase during prophase with a subsequent return to the average interphase value during metaphase-anaphase. The human amnion cells showed no significant change at prophase but there was a 52 to 56 per cent drop in phenylalanine incorporation at metaphase-anaphase as compared to the average interphase rate. Colcemide was used on the hamster cells to study the effect of a prolonged mitotic condition on protein and RNA synthesis. Under this condition, uridine incorporation was extremely low whereas phenylalanine incorporation was still relatively high. The drastic reduction of RNA synthesis observed under mitotic conditions is believed to be due to the coiled condition of the chromosomes. The lack of a comparable reduction in protein synthesis during mitosis is interpreted as evidence for the presence in these cells of a relatively stable messenger RNA.

PERSISTENT POLIOVIRAL INFECTION OF INTACT HUMAN AMNIOTIC MEMBRANE WITHOUT APPARENT CYTOPATHIC EFFECT

Gresser, Ion (Children's Hospital Medical Center, Boston, Mass.), Charles Chany, and John F. Enders. Persistent polioviral infection of intact human amniotic membrane without apparent cytopathic effect. J. Bacteriol. 89:470-475. 1965.-Poliovirus type I multiplied in organ cultures of the intact amniotic membrane. The behavior of the virus in this system differed markedly from that observed in monolayer cultures of trypsinized amnion cells, since replication of new virus was demonstrable throughout a period as long as 3 months, extensive cellular destruction was not apparent, and only a small proportion of cells were found to be infected at a given time. It seems likely that the chronicity of infection is conditioned essentially by the persistent insusceptibility to polioviral infection of the large majority of cells (relative to monolayer cultures) rather than to interferon, which was present in the culture fluids. It was postulated that the greater suceptibility of cultured amnion cells to infection, as compared with cells of the intact membrane, is due in part to the enhancement of phagocytic activity attendant upon trypsinization and cultivation of the amnion cells in monolayers. Amniotic and chorionic membranes thoroughly washed free from blood contain and release in vitro antibody to poliovirus I and other viruses. Appreciation of this phenomen may be important in attempts to isolate viruses from infected tissues.

CELL-FREE VARICELLA-ZOSTER VIRUS IN TISSUE CULTURE

Infected human thyroid tissue cultures have been found to yield free V-Z virus on ultrasonic disintegration and some virus is also present in the fluid phase of intact tissue cultures, while the yield of virus from infected human amnion cells is very low and no free virus is found in the fluid phase. Thyroid cultures are more susceptible to infection with V-Z virus, and the infected cultures are a better source of complement-fixing antigen, than are amnion cultures.

The lack of free virus in infected amnion tissue cultures cannot be attributed to protection by interferon. It also seems likely that if any infectious virus were released it would be more likely to be adsorbed to normal cells than to be inactivated, but as no secondary foci appear in amnion monolayers we conclude that infective virus is not released into the medium.

It is suggested that the virus in thyroid cells is present in a more complete form than that in amnion cells.

We are grateful to Dr R. M. Rawcliffe of Birkenhead General Hospital and Dr F. Whitwell of Broadgreen Hospital, Liverpool, for arranging the supply of thyroid tissue.

SOME EFFECTS OF ATROPINE ON SMOOTH MUSCLE

Contractions of the nerve-free smooth muscle of the chick amnion, either spontaneous or in response to electrical or mechanical stimuli, are potentiated by high conentrations (10(-5) g/ml.) of atropine sulphate. In addition hyoscine, homatropine, lachesine, propantheline bromide and atropine N-methyl and atropine N-butyl salts potentiate spontaneous activity in the amnion. The effects of atropine do not appear to depend on inhibition of cholinesterase; on labilization, stabilization or depolarization of the muscle cell membrane; or on an increase in metabolism. It is suggested that the effects are the result of blockade of the muscarinic acetylcholine receptors. The way in which this may facilitate the conducted response is discussed.