Dissemination or amplification of Japanese encephalitis (JE) virus in summer through the pig-mosquito-pig cycle was consistently found in the Natori District of Miyagi Prefecture over a period from 1964 to 1974 when the time of initial appearance of vector mosquitoes was examined and when antibody response was pursued in pigs at weekly intervals. Analysis of the results of the field survey revealed a gradual decrease in the breeding number of vector mosquitoes (Culex tritaeniorhynchus) and a delay in the date of appearance of vector mosquitoes toward 1974. These changes were correlated to the obvious decline of JE infection recently noticed among pigs and human beings in Miyagi Prefecture. Then several factors which might affect the breeding density of vector mosquitoes were discussed. As a result, the meteorological conditions, especially the sum total of atmospheric temperatures, were found to have a positive correlation with the density of mosquitoes. The effect of spraying insecticides on rice fields, however, did not reveal a positive correlation to the breeding of vector mosquitoes.
Antigen (para-aminobenzen sulfonic acid conjngated with guinea pig serum albumin) with Freund's complete adjuvant was injected into the footpad of the right hind limb of guinea pigs. The number of cells forming rosettes with RRBC and EAC was counted in the inguinal anraxillary lymph nodes on both sides, mesenteric lymph node, spleen and Peyer's patch in the immunized animals. Changes in the T and B cell proportion were investigated in the time couse after immunization. The results obtained are as follows. 1) The T-cell proportion reached a maximum in the regional lymph node on the 1st day after immunization, and the B-cell proportion on the 3rd day after immunization. 2) The increase in the T-cell proportion in the regional lymph node on the 1st day might be dependent on the number of T cells migrating from the thymus, but not on the proliferation of these cells present in the lymph node. 3) Some of the B cells having proliferated in the lymph node might be originated from other lymphoid tissues. 4) Radiation-resistant cells might play an important role in the initiation of lymphocyte trapping.
Various R factors were transferred from Shigella to Salmonella typhimurium LT-2 to examine the effect of these factors on the virulence of this organism for mice. The 50% lethal dose of the R+ strains of LT-2 varied from strain to strain. No correlation could be found between changes in virulence and those in character of any R factor. An R factor that had rendered the host strain the least virulent was subjected to further studies. The R factor carried by this strain was transferred to wild type LT-2. R+ strains thus obtained were examined for several respects. They varied again in virulence from strain to strain. Then, they were examined for the structure of the cell wall by the aggulutination test with antisera against the known wall polysaccharide mutants of LT-2, as well as by the test of susceptibility to bacteriophage specific for a cell wall component. The results obtained clearly indicated that the less vilulent strain carrying the R factor lacked some of the polysaccharidecomponents of the cell wall which might determine the virulence of the strain. In relation to this, the R factor transferred to the LT-2 mutants of known wall polysaccharide deficiency did not increase the low virulence of its host bacterial strain. Thus, it was concluded that the decrease in virulence of the R+ strains of S. typhimurium LT-2 was not caused by the function of any R factor, but by the nature of the wall polysaccharide of the host bacteria which might be advantageous for receiving the transfer of R factors.
A simplified method was devised for the purification of staphylococcal enterotoxin A on a large scale. In it, a supernatant fluid from the 48-hour culture of Staphylococcus aureus 13 N-2909 in 4% NZ-amine was subjected directly to chromatography on Amberlite CG-50 at first, then to CM-cellulose column chromatography, and finally to Sephadex G-75 gel filtration. The purified toxin preparation obtained was studied for physicochemical properties. purified toxin preparation obtained was studied for physicochemical properties. As a result, 380 mg of enterotoxin A, with a purity greater than 99%, was obtained from 80 liters of culture filtrate. The overall recovery of the toxin was calculated to be about 36%. The purified preparation gave a maximum absorption at 277 nm and a minimum absorption at 250 nm. It was proved both immunologically and physicochemically that the toxin was homogeneous protein. No nucleic acid, carbohydrate, or lipid was detected in the toxin. The sedimentation coefficient (S20w) of the purified toxin was 2.71 S. Its molecular weight was estimated to be 26, 000 by gel filtration on Sephadex G-75, 27, 000 by SDSpolyacrylamide gel electrophoresis, and 30, 000 by sedimentation equilibrium. The presence of two major components was demonstrated by the isoelectric focusing technique. The isoelectric point of the principal component was determined to be pH 7.0 at 20 C. The toxin showed the 50% loss of its serological reactivity when heated at 60 C for 3 hours or at 80 C for 5 hours. It was completely inactivated when heated at 100 C for 2 hours. Amino acid analysis revealed that the toxin consisted of 214 amino acid residues.