Formation of prominent multinucleated giant cells (MGC) was observed in monolayers of a clonal line of BHK-21 cells (BHK-21-528) when infected with Japanese encephalitis virus (JEV). MGC were first observed 3 to 4 days after infection and cytopathic changes proceeded thereafter. Formation of MGC is a typical cytopathic change in this clonal cell line. Virus titer in 50%, tissue culture infective dose (TCID₅₀) equaled that in 50% MGC-forming dose. Virus titer in TCID₆₀ was approximate to plaque-forming units (PFU) in the same host cells. An ability of JEV to form MGC was maintained at least for six serial passages in BHK-21-528. It was inactivated by heating at 56 C for 3 min. All JEV strains, except an attenuated live vaccine strain, induced formation of MGC in BHK-21-528 cells. Red blood cells of several animal species were not adsorbed to MGC induced by JEV. The MGC-forming ability of JEV was specifically neutralized by anti-JEV serum. By fluorescence antibody technique, the MGC were specifically stained by anti-JEV antibody conjugated with fluorescein isothiocyanate. Immunization of animals with lysates of the MGC resulted in production of antibodies against JEV, but no antibody against other viruses which have been reported to induce MGC formation. From these evidences, it was concluded that JEV induced formation of MGC in BHK-21-528.

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Antigenic components of Mahoney strain (poliovirus type 1) involved in virus neutralization reaction were analyzed with mutant Mahoney strains resistant to inhibitors in equine serum (inhibitor-resistant mutants) by means of the kinetic neutralization test. It was shown that absorption of anti-Mahoney serum with five inhibitor-resistant mutants yielded sera with different antibodies, of which three had distinct specificities and two specificities possibly partly related to one of those three sera. Further, it was found that stepwise selection of Mahoney variants resistant to one, two, three and four different inhibitors resulted in gradual deviation of its antigenic composition from that of the original strain. From these results, the possible presence of three or more distinct antigenic determinant sites on the surface of Mahoney strain was indicated.

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Eighteen isolates of anaerobic coryneforms from human bone marrow and skin and four type strains of Propionibacterium were studied chemically, biochemically and antigenically. All of the isolates were identified as Propionibacterium acnes; of the 18 isolates, 16 belonged to serotype I and two to serotype II. By means of gas liquid chromatography and mass spectral analysis, a large amount of iso-type fatty acids, such as iso-pentadecanoic and iso-heptadecanoic acids were detected in whole cells of isolates and type strains. Antitumor and adjuvant effects of the isolates and type strains were found to differ considerably among the strains. One of the isolates, P. acnes C-7, which showed potent biological activities was fractionated by hot phenol-water extraction. The resulting insoluble middle layer was found the most effective in tumor protection, adjuvant action in immune response and phagocytic activity in mice.

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Glycine, known to inhibit the synthesis of a peptidoglycan component of the bacterial cell wall, was effective in eliminating drug resistance of Escherichia coli K12 JE2100 strain harboring the R100-1 factor, although in lower frequencies than that of sodium dodecyl sulfate (SDS). The action of glycine was found to be less effective on the same R factor in JE177 strain, and not effective on the F factor in W6. Infection of R factors from R⁺ cells to R^- cells was found to take place in the glycine broth as efficiently as in broth without glycine. This might result in lowering the apparent efficiency of the action of glycine on those plasmids. The segregation patterns of drug-susceptible clones obtained by the glycine treatment were different from those obtained after the SDS treatment. These results coupled with other evidences suggest that the mode of action of glycine on R⁺ cells may be different from those of other curing agents and may involve mechanisms other than selection of R^- or drug-susceptible segregants that are present in R⁺ culture.

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An epidemiological investigation was carried out to identify and determine the serotypes of Streptococcus mutans from carious lesions of young Japanese children. For this purpose, a direct fluo-rescent antibody technique was mainly used. Fluorescein isothiocyanate-conjugated antibodies were prepared for the five known serotypes of S. mutans. Cross reactions and nonspecific reactions were eliminated by adsorption, counterstaining, or DEAE-cellulose column chromatography. Agar-gel immunodiffusion was used to distinguish between serotypes a and d. The epidemiological survey suggested that serotype c strains were most prevalent in dental plaques of Japanese children. The d and e serotypes were rare and serotypes a and b were not detected. It was also noted that more than one serotype of S. mutans could be found in the same locus of a carious lesion and that there might be no relationship between the degree of caries and the causative serotype(s) of S. mutans.

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Normal mice have a large number of background anti-trinitrophenyl (TNP) antibody-forming cells (AFC) in their spleens (about 40-50 anti-TNP PFC/ 10⁶ cells). We investigated this among several mouse strains, i.e., C57BL/6, C3H/He, Balb/c, ddd, and ICR mice, and found that all strains had a similar number of anti-TNP PFC (plaque-forming cells). Developmental aspects of background anti-TNP PFC in the ontogenic process were also investigated. The number of anti-TNP PFC increased logari thmically during the first few days of age, reached a peak on the 13th day and attained a constant value within 30 days. Neonatal thymectomy did not decrease the number of background anti-TNP PFC but such treatment decreased the anti-TNP PFC response to TNP-HRBC (horse red blood cells) immunization. Germ-free ICR mice had a number of background anti-TNP PFC similar to that of conventional ICR mice. Avidity of background anti-TNP PFC was compared among mice of several ages and it was shown that there were no differences among them. These results suggest that the occurrence of these background anti-TNP PFC is not elicited by the immune response but by the natural maturation of precursors of AFC without antigenic stimulation.

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Injection of endotoxins (bacterial lipopolysaccharide: LPS) several days prior to immunization causes the suppression of antibody response. The suppressive effects of several kinds of LPS preparations on the plaque-forming cell (PFC) antibody response in the spleen of mice were examined after immunization with sheep red blood cells (SRBC). Glycolipids obtained from heptoseless mutants (Re form) of salmonella or its lipid A preparation coupled artificially with bovine serum albumin (BSA) are capable, like LPS obtained from a wild type (S form) strain, of inducing suppression of the PFC response, while alkaline-detoxified LPS can not. The refractory periods of the PFC response induced by LPS injection last only a few days. However, the use of cyclophosphamide (CY) together with LPS can extend the refractory periods of antigenic stimulation for several weeks. Injections of LPS and CY can also induce unresponsive states of OH agglutinin antibody response to antigenic stimulation with formalin-killed organisms of Escherichia coli or Salmonella enteritidis (presumably both thymusindependent antigens). These unresponsive states induced by LPS and CY are easily terminated by a transfer of syngeneic bone marrow cells but not by thymocyte transfer.

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