Pulmonary tumours in Syrian hamsters following inhalation of 239PuO2

Syrian hamsters were exposed to various levels of aerosolized 239PuO2 particles to attain a range of initial lung burdens (medians ranged from 40 to 144 nCi). They were allowed to live without sacrifice and had gross and microscopic tissue examinations at death. Over a range of median lung doses from 4-12 000 rad there was an average 2 per cent incidence of malignant tumours (adenocarcinomas) and 9 per cent incidence of total tumours (primarily adenomas). Some of these results are consistent with those from other laboratories using plutonium oxide aerosols but they represent considerably lower lung tumour incidences than previously observed in this laboratory using aerosols of 238PuO2-ZrO2 particles.

In vitro comparison of foot-and-mouth disease virus subtype variants causing disease in vaccinated cattle

Foot-and-mouth disease virus isolates of types O, A and SAT 2, from diseased animals in herds routinely vaccinated twice a year were compared antigenically with the vaccine strains in the complement-fixation, neutralization and radial immunodiffusion tests. It was found that strains which had readily infected vaccinated cattle had R values against the vaccine strain in the complementfixation and radial immunodiffusion tests of 30 or less, while strains causing primary outbreaks with little spread had R values of 30-40. Threefold differences in humoral neutralizing antibody concentration between the field variant and the vaccine strain in sera from vaccinated animals were likely to be significant in terms of protection.

The role of sheep and goats in the epizootiology of foot-and-mouth disease in Kenya

The pathogenicity of two bovine field strains of virus for indigenous goats was examined in the laboratory. The goats failed to develop clinical disease or become virus carriers although the majority showed a definite immune response. A field survey in a foot-and-mouth disease enzootic area showed that the indigenous sheep and goat populations were frequently exposed to infection as evidenced by a high proportion of sero-positive animals but the incidence of virus carriers was very low in goats and no carriers were detected in sheep.

Lung response to localized irradiation from plutonium microspheres

Uniform spherical 10-micrometer diameter particles of ZrO2 ceramic, containing various concentrations of PuO2, have been injected into the jugular vein of Syrian hamsters with subsequent permanent lodgement in the lung capillaries. The number of particles injected has varied from 2000 to 2 000 000 and the specific activity has been from 0.16 to 59 pCi/sphere so that lung burdens range from 0.2 to 700 nCi. To date, approximately 3000 hamsters have been committed to the experiment and two-thirds have died--the expected rate for normal animals. Little biological damage has been observed, and only five primary lung tumours have been found that may be due to radiation delivered to the lung. To provide a comparison to more uniform radiation, soluble polonium has also been instilled intratracheally. Results from the microspheres suggest that localized lung irradiation alone is not sufficient cause for tumour induction and is much less hazardous than diffuse exposure.

The pathogenicity of bovine strains of foot and mouth disease virus for impala and wildebeest

Impala (Aepyceros melampus) and wildebeest (Connochaetes taurinus) were infected with bovine strains of foot and mouth disease virus by intradermolingual inoculation. No clinical signs developed in the impala but mild atypical lesions developed in the tongues of the wildebeest with generalized spread to one foot in two of the eight animals exposed. All the impala but only some of the wildebeest developed viraemia. No virus could be isolated from any tissues in either species after the 7th day following virus inoculation. Immune response occurred in both species. A field survey revealed few animals of either species with significant antibody titers and no virus 'carriers' were found.

The effect of repeated vaccination in an enzootic foot-and-mouth disease area on the incidence of virus carrier cattle

A comparison was made of the incidence of foot-and-mouth disease virus ;carrier' cattle in an unvaccinated enzootic area and an area where routine 6-monthly vaccination with an inactivated vaccine had been carried out for 3-4 years. The incidence of carriers in the vaccinated area was 0.49% as compared to 3.34% in the non-vaccinated area. The results indicate that, provided the immune status of the vaccinated herd is maintained at a level sufficient to prevent outbreaks of clinical disease and the re-introduction of virus is prevented through livestock movement controls, it should be possible to eradicate the disease from an enzootic area through vaccination.

The foot-and-mouth disease virus subtype variants in Kenya

The subtype variants found in Kenya in the past ten years have been studied. The type O and type SAT 2 subtypes have a distinct geographical distribution which appears to be associated with livestock movement patterns. The type A viruses have a greater tendency to antigenic variation and their geographical distribution is less distinct. In type C only minor differences exist between the three viruses studied.

Cell growth and division. V. Error analysis of the Collins-Richmond equation

Error propagation in the Collins-Richmond equation is analyzed in order to obtain the ratio of the fractional error in rate of cell volume increase to the fractional error in each experimental variable. Typical data are analyzed numerically for the total errors resulting from counting statistics, from spectral broadening, and from volume calibration shift. The measurement of 10(4) cells can give a precision of better than 10% in the volume growth rate with a volume resolution of 3%.

Density invariance of cultured Chinese hamster cells with stage of the mitotic cycle

Isopycnic banding of Chinese hamster line CHO cells in Ficoll gradients shows that a population in balanced, exponential growth is very homogeneous with respect to density, the coefficient of variation of the density distribution spectrum being less than 5% of the mean reduced density (i.e. density minus one). Similar measurements on synchronized cultures indicate that reduced density varies by less than 2% around the life cycle. The mean density of CHO cells in F-10 growth medium is calculated to be 1.051 after correction for osmotic effects of the Ficoll gradient.

In vitro method for safety testing of foot-and-mouth disease vaccines

The susceptibility of the tissue culture system to small amounts of residual live virus was not influenced by the inactivated antigen present. The depth of inoculum over the cell sheet did not affect results. Negative cultures frequently gave positive first (but not second or later) sub-cultures.Baby hamster kidney cells were always more sensitive than cattle tongues to infection with any of the strains used.Confidence in the safety test depends on the number of vaccination doses used; the tissue culture test can be made much more reliable than the cattle test because it is not limited to the 15 ml. of inoculum that restricts the cattle test.

Cell growth and division. IV. Determination of volume growth rate and division probability

Volume growth rate and division probability functions for mammalian cells have been determined as functions of cell volume with good reproducibility and statistical precision using Coulter volume spectrometry and the equations of the Bell model. Results are compared with independent measurements on synchronous cultures. The slow rate of volume dispersion requires that the growth rate F(tau, V) be closely proportional to volume for cells of a given age. However, when F(tau, V) is averaged over the age distribution of a population in balanced exponential growth to give the growth rate function f(V), the latter may rise more steeply than V.

The effect of thymidine on the duration of G1 in Chinese hamster cells

The generation time of a Chinese hamster cell line was varied by the use of different lots of sera in the culture media. Analysis of the division waves following thymidine synchronization showed that lengthening of the generation time was a result of an increase in duration of the G(1) phase and that thymidine treatment reduced the duration of G(1) back to its minimum value.

Cell growth and division. I. A mathematical model with applications to cell volume distributions in mammalian suspension cultures

A mathematical model is formulated for the development of a population of cells in which the individual members may grow and divide or die. A given cell is characterized by its age and volume, and these parameters are assumed to determine the rate of volume growth and the probability per unit time of division or death. The initial value problem is formulated, and it is shown that if cell growth rate is proportional to cell volume, then the volume distribution will not converge to a time-invariant shape without an added dispersive mechanism. Mathematical simplications which are possible for the special case of populations in the exponential phase or in the steady state are considered in some detail. Experimental volume distributions of mammalian cells in exponentially growing suspension cultures are analyzed, and growth rates and division probabilities are deduced. It is concluded that the cell volume growth rate is approximately proportional to cell volume and that the division probability increases with volume above a critical threshold. The effects on volume distribution of division into daughter cells of unequal volumes are examined in computer models.

Cell growth and division. II. Experimental studies of cell volume distributions in mammalian suspension cultures

Experimental proof is given that the volume distribution spectrum of mammalian cells in suspension culture can be determined accurately with a Coulter spectrometer. Stable spectra corresponding to the predictions of a mathematical model are observed under favorable conditions of growth. Cell volume spectrometry appears to be a useful method for diagnosing the state of the culture with respect to past uniformity of growth rate and present population age distribution. In addition, it offers a method for quantitative study of the laws governing cell growth and division.

Life cycle analysis of mammalian cells. 3. The inhibition of division in Chinese hamster cells by puromycin and actinomycin

Analysis of the effects of actinomycin and puromycin on the G(2) and mitotic parts of the life cycle in Chinese hamster ovary cells grown in suspension and synchronized by thymidine treatment has been carried out. Rates of division of partially synchronized cell populations were measured in the presence and absence of the drugs, and various controls were performed to test for absence of complex side effects. Actinomycin produces a block 1.9 hr before completion of division, while puromycin produces a block almost coinciding with the initiation of mitosis. Evidence is presented that the puromycin block may be a double one, inhibiting one kind of protein synthesis that virtually coincides with the beginning of mitosis and another that occurs about 8 min earlier. The data are interpreted in terms of the time interval between messenger formation and its associated protein synthesis in this region of the life cycle. The various events studied have been provisionally mapped in the G(2) and mitotic periods of the life cycle.