In order to study the effects of exposure to atomic bomb radiation on the immune competence of man, the proportions of peripheral blood lymphocyte subsets (subpopulations) were determined by an indirect immunofluorescence antibody assay using monoclonal antibodies and fluorescence microscopy. The study was based on a total of 104 Adult Health Study participants in Hiroshima, including 29 individuals exposed to 100⁺ rad, 46 exposed to 1-99 rad, and 29 0 rad controls.
No change in the proportion of Leu-1 positive cells (total T cells) and Leu-2a positive cells (cytotoxic/ suppressor T cells) and the ratio of Leu-3a/Leu-2a was observed with age, while Leu-3a positive cells (helper/ inducer T cells) decreased with age and HLA-DR positive cells (B cells and monocytes) increased with age, with the differences occurring predominantly in the oldest age group (age > 75). The proportion of HLA-DR positive cells was higher in males, but there was no significant sex difference in the proportions of other cell types and the ratio of Leu-3a/Leu-2a. Radiation exposure did not significantly affect the proportions of Leu1, Leu-2a, Leu-3a, and HLA-DR positive cells and the ratio of Leu-3a/Leu-2a. No interaction between the effects of age and radiation exposure was demonstrated.

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Rats were kept in a metabolic cage through which air containing tritiated water vapor was passed at a constant rate. Tritium activity in their blood and urine was found to increase with increase in tritium activity in the air. The absorption ratio of tritiated water (the ratio of tritium activity in the blood or urine to that in air) was constant even with change in humidity. By continuous inhalation of tritiated water vapor (10.1 pCi/ ml air), activity in urine increased gradually with time and attained to about 70 nCi/ml after 140 h. The initial rate of tritium intake was found to be 1.4 × 10^-4 C Bq/min/rat, where C is tritium activity in ambient air (Bq/m³). Tritium activity in various tissues except adipose tissue was similarly increased after starting exposure of the rats to tritiated water vapor. In addition, tissue-bound tritium activity was also found to be 3-10% of wet-tissue activity.

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The effects of dimethylsulfoxide (DMSO) on radiation-induced G₂ delay and on each stage in mitotic phase were studied. The G₂ delay was reduced by the postirradiation treatment of Chinese hamster ovary cells by over 2%. DMSO at 2% had no effect on the progression of the cells through metaphase, anaphase or telophase, when added after mechanical collection of cells at the mitotic phase. DMSO over 5%, and particularly over 7%, led to a retardation at metaphase, with little effect on anaphase or telophase.

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The radiosensitivity of primary cultured goldfish cells (Carassius auratus) was investigated by colony formation assay. The radiosensitivity of cells from two varieties of goldfish, which show different sensitivity to lethal effect of ionizing radiation in vivo, was almost identical. Primary cultured cells from diploid, triploid and tetraploid fish retained their DNA content as measured by microfluorometry, and the nuclear size increases as ploidy increases. However, radiosensitivity was not related to ploidy.

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The relation of heat shock protein (HSP) synthesis and development of thermotolerance was compared in Chinese hamster V79 cells of low, and mouse L cells of high, thermosensitivities. Thermotolerance was induced by step-up heating (42°C, 2 hr and 44°C). Cycloheximide did not inhibit the development of thermotolerance in V79 cells. In contrast, no apparent thermotolerance was induced by step-up heating (42°C, 1 hr and 44°C) in L cells. In V79 cells, as shown by two-dimensional gel electrophoresis, two 68-kilodalton heat shock proteins (68-kDa HSPs) were synthesized constitutively and increased markedly when cells were heated at 42°C for 2 hr. Cycloheximide inhibited more than 90% of the total protein synthesis including the 68-kDa HSPs. In contrast, no 68-kDa HSP was detected in L cells at 37°C. When L cells were heated at 42°C for 1 hr, 68-kDa HSP was detected by fluorography but not by Coomassie blue staining. These results suggest 1) that cells constitutively synthesizing 68-kDa HSP had low thermosensitivity and could be thermotolerant without de novo synthesis of the protein, and 2) that cells not synthesizing 68-kDa HSP had high thermosensitivity and could not be thermotolerant because the cellular 68-kDa HSP content was low even when the protein was newly synthesized.

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A hybrid cell clone PX1 was isolated by fusing UV sensitive XP20S(SV)neo, an SV-40-transformed, neomycin-resistant xeroderma pigmentosum (XP) cell line, and Pt K2, a rat kangaroo (Potorous tridactilis) cell line. The UV-survival curve of PX1 cells fell midway between those of Pt K2 and XP20S(SV)neo cells, since mean lethal doses(D₀) were 2.5, 4.7 and 0.27 J/m² for PX1, Pt K2 and XP20S(SV)neo, respectively. Amounts of unscheduled DNA synthesis (UDS) after UV, relative to normal human cells, were 60.4% for Pt K2, 37.7% for PX1 and 0.1% for XP20S(SV)neo. Such relative UDS capacities for excision repair of Pt K2, PX1 and XP20S(SV)neo were also consistent with the respective relative capacities of host cell reactivation (HCR) of UV-irradiated Herpes simplex virus. Apparently, there was no single Pt K2 chromosome in the PX1 cells. One possibility is that a gene which may account for the partial restoration of the UV resistance has been transferred from Pt K2 to PX1.

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Mutational nucleotide sequence changes by ultraviolet light (UV) in the gene for Escherichia coli CAMP receptor protein (CRP) were analyzed. Transitions were most the frequent mutations and occurred at pyrimidine-pyrimidine sequences. Most transitions were GC to AT base changes at 3'' cytosine of 5''-pyrimidinecytosine-3'' sequences, supporting the concept that pyrimidine(6-4)pyrimidone, Pyr(6-4)Pyo, photoproduct is a principal pre-mutagenic lesion for transition mutations induced by UV. Transversion and frameshift mutations were also found.

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The combined effects of an iodine contrast medium and X-rays on the number of colony forming units (CFUs) in mice bone marrow were examined in vitro and in vivo. No changes were observed in the number of CFUs per 10⁵ nucleated bone marrow cells, when the contrast medium alone was added to bone marrow cell suspensions at concentration of 0.5 and 5.0%. X-irradiation of the suspensions above a dose of 50 R reduced the number of CFUs per 10⁵ cells. The irradiation of the suspensions in the presence of the contrast medium produced further decrease in the number of CFUs per 10⁵ cells, depending on the concentration of the medium used. No enhancement of the X-ray effect was observed when mice were injected with the contrast medium at a dosage 10 times higher than that used in X-ray diagnosis in man and irradiated immediately. Thus, the iodine contrast medium sensitized hematopoietic stem cells to X-rays in vitro but did not in vivo.

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