DNA strand breaks measured within 100 milliseconds of irradiation of Escherichia coli by 4 MeV electrons.
(41/1228)
A method was developed in which E. coli cells were irradiated with four MeV electrons and transferred to alkaline detergent within a fraction of a second. This technique minimizes the amount of repair of radiation damage before analysis without the necessity of using physical or chemical treatments to inhibit repair and alter the physiological condition of the cells. The yield of DNA strans breaks formed in covalent circular superhelical lambda DNA molecules superinfecting E. coli lysogens was about 4-fold greater when the cells were irradiated in oxygen than when they were irradiated under nitrogen anoxia. The same yields were obtained in phosphate buffer at 3 degrees and 22 degrees as well as in growth medium at 37 degrees, and the yields were not altered by the polA1 mutation. When E. coli lysogenic cells superinfected with lambda were irradiated with doses sufficient to introduce at least seven breaks in the phage DNA, the chromosomal DNA and the superinfecting phage DNA sedimented similarly in alkaline sucrose gradients, indicating that both DNAs were broken to a similar extent during irradiation. However, the yield of breaks calculated for chromosomal DNA in similar experiments was greater than the yield calculated from the first break introduced into covalent circular lambda DNA molecules. These apparently contradictory results are explicable either if the initial break in a superhelical molecule occurs with an efficiency different from that for subsequent breaks, or if the pulsed electron radiation produces a high proportion of double-strand breaks. (+info)
Modification of the immunogenicity and antigenicity of rat hepatoma cells. I. Cell-surface stabilization with glutaraldehyde.
(42/1228)
gamma-Irradiated rat hepatoma cells are immunogenic in syngeneic WAB/Not rats, so that immunized animals are protected against tumour-cell challenge and circulating tumour-specific antibody is produced. Treatment of the immunizing cells with glutaraldehyde at concentrations of 0.001% or greater for 30 min rendered these cells non-protective in tumour-rejection tests and no longer able to induce significant formation of specific antibody. However, tumour-specific antigens were shown to be expressed upon treated cells; they specifically bound tumour-specific antibody from syngeneic immune sera assessed in indirect membrane-immunofluorescence tests. Also, these cells specifically absorbed antibody from immune or tumour-bearer sera, as demonstrated in the indirect membrane-immunofluorescence test or a complement-dependent 51Cr-release test. Alloantigen expression was not influenced by glutaraldehyde treatment, although glutaraldehyde-treated hepatoma cells failed to induce alloantibody formation in KX/Not rats. Polyacrylamide-gel electrophoresis of treated cells, surface-labelled with 125I, indicated that extensive cross-linking of the surface protein occurred as a result of glutaraldehyde treatment. The present findings establish that although the expression of a tumour-specific antigen is necessary for the induction of immuno-protection against tumour-cell challenge, this alone is not a sufficient condition for eliciting tumour immunity. (+info)
Adverse effects of intrathecal methotrexate in children with acute leukemia in remission.
(43/1228)
A toxic syndrome characterized by fever, headache, and vomiting, lasting 2-5 days, occurred in 61% of 39 children with acute leukemia in complete remission, receiving central nervous system prophylaxis with intrathecal methotrexate, and in 14% of 34 children receiving the same plus cranial radiation. The syndrome was accompanied by pleocytosis with lymphocytes, monocytoid cells, and neutrophils. There was evidence of cumulative Mtx toxicity, since the toxic syndrome occurred mostly after the third and fourth dose and did not recur with longer intervals between doses. The incidence of the syndrome was significantly reduced by the use of Elliott's B solution as Mtx diluent, rather than water or normal saline. The occurrence of pleocytosis and toxic clinical syndrome was also significantly reduced in patients receiving concomitant cranial radiation, probably due to the lympholytic action of radiotherapy and the depressed cellular response of irradiated tissues. The use of Elliott's B solution as diluent for IT Mtx and an appropriate interval between Mtx doses are suggested for prevention of this toxic syndrome. (+info)
Effect of bleeding on hematopoiesis following irradiation and marrow transplantation.
(44/1228)
In previous studies, bleeding after irradiation did not affect the rate of regeneration of endogenous spleen colony-forming cells, but induced an early (4-6 days after irradiation) appearance of erythrocytic colonies which differentiated and disappeared by days 7-8. This "abortive" wave was associated with a similarly abortive wave of splenic 59Fe uptake. The present experiments were done to determine whether or not an abortive wave of erythropoiesis could be induced in the transplanted, exogenous stem cell system. Lethally irradiated mice were given normal bone marrow cells and one-half of the group were bled of about one-third their blood volume within 4 hr of irradiation. Groups were killed on days 3-10 after irradiation. Seventeen to twenty hours prior to killing, 59Fe was injected. Hematocrits, spleen weights, colony numbers, and per cent 59Fe uptake were determined. Hematocrits of bled mice averaged about 70% of those of cell-injected controls. Spleen weights, colony counts, and per cent 59Fe uptake per spleen began to increase about 1 day earlier in bled mice (days 4-5 as compared to days 5-6), and rates of increase were the same as those of controls. However, no abortive wave of erythropoiesis was detected. A large cell dose resulted in earlier increases in all parameters than a small dose. Thus, bleeding after injection of cells produced results similar to those obtained by increasing the cell dose. The inability of bleeding to induce an early abortive wave of erythropoiesis in transplanted as compared to endogenous colony-forming systems may reflect differences in the cell cycling characteristics of these systems. (+info)
Thymus dependence of the IgA response to sheep erythrocytes.
(45/1228)
The thumus dependence of the IgA response to sheep red blooc cells (SRBC) was studied by means of cell transfer experiments in mice. Only low numbers of IgM-, IgG- and IgA-plaque-forming cells (PFC) were observed in those recipients which received only spleen cells from adult thymectomized, irradiated and bone marrow-reconstituted mice (B cells). High numbers of IgM-, IgG- and IgA-PFC were observed when B cells and educated T cells were transferred to the recipients. Evidence is provided that B cells committed to IgA synthesis require the same degree of interaction with T cells as B cells committed to IgM synthesis, but a lower degree of interaction with T cells than B cells committed to IgG synthesis. (+info)
Neutralization of Chlamydia trachomatis in cell culture.
(46/1228)
Neutralization of Chlamydia trachomatis was assayed by the decrease in inclusion-forming units in baby hamster kidney cells grown in culture. Five percent fresh guinea pig sera increased neutralization titers of rabbit antisera 100- to 1,000-fold but had no effect when normal rabbit sera were tested. Neutralization of a type A or B trachoma isolate was strain specific. Neutralization by human eye secretions and sera also was demonstrated when guinea pig sera were included in the test. All of the six human sera tested showed strain specificity against types A or B, in agreement with typing by the fluorescent antibody technique. (+info)
The inhibiting effect of indomethacin on the disruption of the blood-aqueous barrier in the rabbit eye.
(47/1228)
The aqueous flare (AF) of an intact rabbit eye was measured by a photoelectric instrument. Local application of prostaglandin E2 (PGE2) and its precursor arachidonic acid (AA) gave an almost identical increase of the AF. The response to AA but not to PGE2 was inhibited by pretreating the eye locally with a solution of indomethacin. The ability of indomethacin to inhibit the aqueous flare response (AFR) to an agent is assumed to indicate that a kind of prostaglandin is the effector of the AF. Indomethacin blocked the AFR to infrared irradiation of the iris and to intravenous administration of endotoxin but not to subcutaneous administration of alpha-melanocyte-stimulating hormone (alpha-MSH). (+info)
Tryptophan photoproduct(s): sensitized induction of strand breaks (or alkali-labile bonds) in bacterial deoxyribonucleic acid during near-ultraviolet irradiation.
(48/1228)
Long-wavelength ultraviolet light (300 to 400 nm) converts L-tryptophan to a photoproduct that is toxic for bacterial cells in dark conditions. We now report that similar photoproducts of l-tryptophan sensitize bacterial deoxyribonucleic acid to 365-nm radiation, increasing the yield of deoxyribonucleic acid strand breaks (or alkali-labile bonds) by approximately 11.5-fold. Evidence is also presented which indicates that thse sensitized deoxyribonucleic acid lesions contribute to lethality for Escherichia coli irradiated with 365-nm ultraviolet light in suspensions of tryptophan photoproducts. (+info)