Immunological effects of wall lipopolysaccharide (LPS) preparations obtained from Vibrio cholerae Inaba 569B, Ogawa NIH 41 and NAG 4715 strains by the hot phenol-water procedure were examined in mice. Although these LPS lack KDO, which are basic components of the core region of most gram-negative LPS, they still have potencies as B-cell mitogens, adjuvants, immunosuppressants, polyclonal B-cell activators and phagocytic stimulants for macrophages. The activities of these V. cholerae LPS on murine immune system seemed to be weaker than those of Salmonella typhimurium LT2-LPS. Among these V. cholerae LPS, NAG 4715-LPS showed the strongest mitogenic activity and phagocytic stimulation, while the potencies of this NAG 4715-LPS for the induction of polyclonal B cell activation, adjuvant effects and immunosuppression did not seem to be greater to those of the other LPS.

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Out of 32 R plasmids isolated from Proteus strains, 17 were found to be temperature sensitive with respect to inheritance in E. coli cells. They were fi^- and classified into incompatibility group T or V. Cells carrying T group Rms273 plasmid were temperature sensitive with respect to growth and conjugal transfer in both E. coli and Proteus. The V group YOR-10 plasmid was stable in Proteus even at 42 C. However, the loss frequency of YOR-10 plasmid in E. coli reached 100% after 4 hr of incubation at 42 C, in spite of stable inheritance at 25 C. Conjugal transfer of the YOR-10 plasmid in E. coli was also strongly inhibited at 42 C. It has been concluded that instability of V group R plasmids in E. coli is due to their thermosensitive inheritance in the progeny cells at high temperatures.

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An unusual regulatory system of cephalosporinase synthesis in Citrobacter freundii has been found. When the bacteria are grown at 20 C, the cephalosporinase is synthesized as a typical inducible enzyme and benzylpenicillin acts as an effective inducer. The enzyme, however, is synthesized in the absence of the inducer at growth temperatures above 25 C. When the growth temperature is shifted from 20 C to 37 C, the induction of enzyme synthesis is observed after about one half of the organism doubling time, but it does not occur in the presence of chloramphenicol. The reverse control mutants, the enzyme constitutive synthesis of which is markedly depressed by benzylpenicillin, were isolated from the C. freundii wild strain. The possibility that the enzyme synthesis is governed by a regulatory system analogous to the i^ts mutant of the lac operon in Escherichia coli was suggested.

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Purified host DNA-suppressing factor (DSF) produced into culture fluid of HeLa C-9 cells infected with measles virus inhibited cellular DNA synthesis in HeLa cells. When purified DSF was added into cultures of synchronous HeLa cells at the early G₁-phase, cellular DNA synthesis was irreversibly inhibited. However, DSF did not affect the stability of native double-stranded DNA nor the chain-elongation of single-stranded DNA in cells of the S-phase.

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Bccause β₂-microglobulin is structurally similar to IgG, the reaction of β₂-microglobulin with Staphylococcal Protein A, which is known to react with the Fc region of IgG, was examined. ¹²⁵I-β₂-microglobulin did not bind to Protein A. This may due to the difference in the amino acid sequence between β₂-microglobulin and the Fc region of IgG.

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The sera obtained from blood of the mice, which had been intravenously injected with LPS several hours in advance, contained some active substance capable of enhancing anti-sheep red blood cell (SRBC) antibody responses in mice. Activity of the sera was still retained after passage through a rabbit anti-LPS antibody-coated Sepharose 4B column, but greatly reduced by passage through a rabbit antimouse thymocyte antibody-coated Sepharose 4B column. The active substance in the sera was eluted through a Sephadex G-200 column at the same position as the serum albumin.
The addition of this substance to B cell rich spleen cell cultures in vitro in the presence of SRBC generated tremendous numbers of antibody forming cells 4 days after the incubation, suggesting that this substance was able to take over the helper function of T cells in thymus dependent antibody responses. However, this substance was not capable of stimulating ³H-thymidine-uptake into cultured spleen cells. The possible role of this substance in the adjuvant effect of LPS is discussed.

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