Murine leukemia virus strains fall into three categories with respect to their ability to propagate in cells of National Institutes of Health (NIH) Swiss and BALB/c mouse embryos. Cultures of NIH cells are 100- to 1,000-fold more sensitive to "N-tropic" strains than BALB/c cell cultures, but are 30- to 100-fold less sensitive to "B-tropic" strains. Some virus strains (dually tropic or "NB-tropic") propagate equally well in both cells. M-MSV pseudotypes show the host-range characteristics of the virus supplying the envelope, both in vitro and in vivo. The host-range characteristics appear to be genetically determined and could not be explained by host-induced modification or virus mixtures. There was no correlation between host range and Gross-AKR or FMR serotype.

A tissue culture cell system for isolation and identification of members of the murine leukemia virus group (the complement fixation for murine leukemia test) was modified to permit the isolation of naturally occurring virus from leukemic and normal mice. The important factors for increasing the sensitivity of the test were the use of National Institutes of Health (NIH) strain Webster Swiss embryo cell cultures and the selection of rat-immune sera having complement-fixing antibodies to tissue culture antigens of both the Gross and FMR subgroups. In all, 163 strains of mouse leukemia virus, from 11 inbred mouse strains, have been isolated. Representative virus isolates were shown to possess the properties of the murine leukemia virus group; i.e., they were chloroform-sensitive, noncytopathic agents which replicated in mouse embryo tissue culture and produced group-reactive, complement-fixing antigen and budding C-type particles visible by electron microscopy. These viruses could serve as helpers in the rescue of Moloney sarcoma virus genome from non-producer hamster sarcoma cells, yielding pseudotypes. All of the 19 field isolates tested were neutralized by Gross passage A antiserum but not by potent antisera to the Moloney, Rauscher, and Friend strains. Virus was recovered regularly from embryos and from the plasma and spleen of adult mice of high leukemic strains. In low leukemic mouse strains, different patterns of virus detection were observed. In C3H/He mice, virus was occasionally present in embryos and was found in 40% of adult spleens. BALB/c mice were virus-negative as fetuses or weanlings, but spleens of more than half of the mice over 6 months of age yielded virus. NIH mice have never yielded virus. In reciprocal matings between AKR and BALB/c mice, virus recovery from embryos was maternally determined. The development of tissue culture isolation procedures made possible for the first time the application of classical infectious disease methods to the study of the natural history of murine leukemia virus infection.

We introduce an intuitive particle-based model of time-symmetric quantum physics that gives a concrete description of what goes on in the time between projective measurements of a quantum system. The time-symmetry in this model means that we ...Physical interpretations of the time-symmetric formulation of quantum mechanics, due to Aharonov, Bergmann, and Lebowitz are discussed in terms of weak values. The most direct, yet somewhat naive, interpretation uses the time-symmetric formulation to ...

25 Mittermayer, C., R. Braun, and H. P. Rusch, Biochim. Biophys. Acta, 91, 399 (1964). 26 Burton, K., Biochem. J., 61, 473 (1955). 7 Ceriotti, G., J. Biol. Chem., 214, 59 (1955). 8 Gornall, A. G., C. J. Bardawill, and M. M. David, J. Biol. Chem., 177, 751 (1949). 29 Mohberg, J. E., and H. P. Rusch, J. Cell Biol., 23, 61A (1964). 30 Hendler, R. W., Anal. Biochem., 7, 110 (1961). 31 Sachsenmaier, W., Biochem. Z., 340, 541 (1964). 32 Sachsenmaier, W., and H. P. Rusch, Exptl. Cell Res., 36, 124 (1964). 33 Kajiwara, K., and G. C. Mueller, Proc. Am. Assoc. Cancer Res., 5, 33 (1964). 34 Jacob, F., S. Brenner, and F. Cuzin, in Synthesis and Structure of Macromolecules, Cold Spring Harbor Symposia on Quantitative Biology, vol. 28 (1963), p. 329. 35Painter, R. B., and R. E. Rasmussen, Nature, 201, 162 (1964).

SummaryMouse hepatitis viruses were readily isolated, by a variety of technics, from pooled feces of weanling mice of the majority of colonies tested. The infection was highly contagious to contacts from a non-infected mouse stock. Evidence is presented that contact infection with hepatitis viruses produced high mortality in infant mice of the non-infected stock.

Summary Seven additional adenovirus serotypes of human origin have been established, including a subtype of type 7, designated 7a. Also, 3 additional adenovirus types of simian origin are reported. It is suggested that the adenovirus group be divided into strains of human, chimpanzee, and monkey origin, with separate series of type numbers.

Sialic acid-based glycoconjugates cover the surfaces of many different cell types, defining key properties of the cell surface such as overall charge or likely interaction partners. Because of this prominence, sialic acids play prominent roles in mediating attachment and entry to viruses belonging to many different families. In this review, we first describe how interactions between viruses and sialic acid-based glycan structures can be identified and characterized using a range of techniques. We then highlight interactions between sialic acids and virus capsid proteins in four different viruses, and discuss what these interactions have taught us about sialic acid engagement and opportunities to interfere with binding.

SummaryThe guinea pig submaxillary gland virus has been successfully propagated in tissue culture, one strain having been carried through 22 serial passages. The tissue culture passage virus produced characteristic intranuclear inclusion bodies in tissue cultures, demonstrated complement fixing and neutralizing antibody responses in guinea pigs infected with animal passage virus, and produced characteristic disease and histopathology in susceptible guinea pigs. Commercial complement consistently contained high titer CF antibody.

Fourteen serologically distinct APC virus types have now been established. Twelve types were recovered from human, and 2 from simian materials.

It has been shown that adenoidal-pharyngeal-conjunctival (APC) viruses are responsible for certain hitherto undifferentiated respiratory illnesses and that they have been associated with certain external diseases of the eye. 1 These viruses produce neutralizing antibodies in human serum. 1 b Nine human and two simian adenoidal-pharyngeal-conjunctival virus serotypes have been delineated to date. 2 When types 1, 3, 4, and 5 are swabbed on the conjunctivas of susceptible volunteers, they regularly produce a moderately severe, self-limited catarrhal conjunctivitis, together with systemic symptoms similar to those of pharyngoconjunctival fever. Volunteers having specific serum antibodies are resistant to the disease. 3 This report describes initial studies with volunteers, studies designed to determine the ability of a formaldehyde-inactivated and a heat-in-activated type 3 APC virus vaccine to ( a ) produce specific neutralizing antibodies in the serum and ( b ) to prevent or modify artificially induced infection and disease. MATERIALS AND METHODS Preparation of Vaccines.— The J.