Sister-chromatid exchanges induced by mitomycin C after exposure of human lymphocytes in G0 to a low dose of X-radiation

Human peripheral blood lymphocytes from 20 donors were exposed in G0 to mitomycin C with and without prior acute irradiation with 0.01 Gy of 250 kVp X-rays. No evidence was found for the radiation having an hormetic effect on the level of sister-chromatid exchanges induced by mitomycin C.     

Bone marrow-derived T lymphocytes responsible for allograft rejection

Lethally irradiated mice reconstituted with syngeneic bone marrow cells were grafted with allogeneic skin grafts 6-7 weeks after irradiation and reconstitution. Mice with intact thymuses rejected the grafts whereas the mice thymectomized before irradiation and reconstitution did not. Thymectomized irradiated mice (TIR mice) reconstituted with bone marrow cells from donors immune to the allografts rejected the grafts. Bone marrow cells from immunized donors, pretreated with Thy 1.2 antibody and C', did not confer immunity to TIR recipients. To determine the number of T lymphocytes necessary for the transfer of immunity by bone marrow cells from immunized donors, thymectomized irradiated mice were reconstituted with nonimmune bone marrow cells treated with Thy 1.2 antibody and C' and with various numbers of splenic T lymphocytes from nonimmune and immune donors. Allogeneic skin graft rejection was obtained with 10(6) nonimmune or 10(4) immune T cells. The effect of immune T cells was specific: i.e., immune T cells accelerated only rejection of the relevant skin grafts whereas against a third-party skin grafts acted as normal T lymphocytes.     

Method of differential staining of sister chromatids for the study of the effects of gamma rays on the frequency of sister chromatid exchange in human lymphocytes]

Human lymphocytes were incubated during two cycles of replication in the presence of 5-bromodeoxyuridine, fixed after a 96 hours cultivation, stained with fluorescenct compound "Hoechst 33258", illuminated with sunlight and repeatedly stained with azureosine. After such a treatment, the two chromatids of metaphase chromosomes are stained with different intensity revealing numerous sister chromatid exchanges (SCE) which could be exactly recorded. In spite of the use if tge standard technique, the frequency of SCE was different in two donors. Irradiation after a 47 hours incubation (mainly G2 stage of the first cycle) increased the frequency of SCE, whereas the irradiation 2 hours before fixation (G2 stage of the second cycle) decreased it. The change of the frequence of SCE produced by irradiation was not proportional to the chromosome length.     

The mediator of cellular immunity. VIII. Effect of mitomycin C on specifically sensitized lymphocytes.

The antimitotic agent, mitomycin C, was used to probe cellular events underlying the expression of acquired resistance to L. monocytogenes in the rat. It was found that thoracic duct lymphocytes from donors primarily immunized with this organism can protect normal recipients against a Listeria challenge and that their ability to do so is inhibited by treatment of the lymphocytes with mitomycin C. Concentrations of the drug which are effective in this regard also inhibit lymphocyte proliferation, but have little if any effect upon RNA or protein synthesis in cells tested at the time of transfer. Yet mitomycin C probably has irreversible effects on lymphocytes in addition to its capacity to block cell replication, for inhibitor-treated immunoblasts fail to localize in peritoneal exudates induced in recipient rats. The inability of mitomycin-treated immunoblasts to extravasate in inflammatory foci is associated with a diminished capacity of specificially sensitized lymphocytes to promote cell division in peritoneal exudates induced by L. monocytogenes. The results illustrate the importance of lymphocyte-macrophage interactions in cellular resistance to infection and give credence to the view that these interactions occur locally at sites of microbial invasion.     

On the response of a cell population to low-dose irradiation

The cell composition of a population of human blood lymphocytes was studied after irradiation at doses of 5 cGy, 1.0 Gy and 5 cGy + 1.0 Gy and the use of a cytokinesis block. The frequencies of uni-, bi- and multinucleate lymphocytes with and without micronuclei (MN) were taken into account. By the standard criterion the frequency of binucleate lymphocytes with MN among binucleate lymphocytes--the donors were characterized as follows: in with reduction of radiosensitivity after irradiation with 5 cGy + 1.0 Gy as compared to the values of radiosensitivity after irradiation with 1.0 Gy only (an adaptive response, AR); in with no change of radiosensitivity after exposure to these doses (no AR); and with an increased ofradiosensitivity after exposure to these doses (syndrome of increased radiosensitivity, IRS). It was found that upon exposure to 1.0 Gy and 5 cGy + 1.0 Gy in some donors with AR, without AR and with IRS the total numbers of damaged cells in the population and the number of binucleate cells with MN were equal. This result calls in question the involvement of the repair mechanism in the alteration of radiosensitivity of lymphocytes in these donors. It was also observed that in the same donors a simultaneous increase (or a decrease in the case of IRS) of the portion of undamaged binucleate cells in the population took place. Our results demonstrate the existence of a new, populational, mechanism involved in the alteration of radiosensitivity after exposure to the adaptive and challenge doses.     

Lack of synergistic effect between X-ray and UV irradiation on the frequency of chromosome aberrations in PHA-stimulated human lymphocytes in the G1 stage.

PHA-stimulated human lymphocytes in the G1 stage were irradiated with UV radiation and X-rays, and the cells were analyzed for chromosomal aberrations in the first mitotic division. The frequency of dicentric chromosomes after single X-irradiation in the G1 stage was about twice the yield in the G0 stage. No increase in the yield of dicentrics was observed after combined irradiation with UV and X-rays. This is contrary to the finding for G0 lymphocytes, where a 2-fold increase of chromosome aberrations was observed. UV irradiation of G1 lymphocytes induced chromatid-type aberrations whereas no significant yield of dicentric chromosomes was observed. This is in agreement with previous findings in Chinese hamster cells in the G1 stage [7]. Irradiation of G0 lymphocytes with UV radiation induce a low frequency of dicentric chromosomes. Thus, the present data indicate that the ratio between chromosome-type and chromatid-type aberrations is different in the G1 and G0 stages in human lymphocytes irradiated with UV radiation.     

Clastogenic action of ellipticine over the cell cycle of human lymphocytes and influence of posttreatments with caffeine and ara-C at G2

The clastogenic potential of the intercalating compound ellipticine, an antitumor alkaloid, has been demonstrated in mammalian cells. To characterize the mechanism of action of this drug over the cell cycle, human lymphocyte cultures from 2 healthy donors were treated with 3 micrograms/ml ellipticine in 30-min pulses during different phases of the cell cycle and analyzed for chromosomal aberrations and sister-chromatid exchanges. The G2 phase was most sensitive in terms of induction of aberrations, followed by S and G1. Chromatid-type aberrations were the most common type of chromosomal damage. Induction of SCEs was significantly high only after treatment at G1, when the frequencies of SCEs doubled. The post-treatment effect of lymphocytes with inhibitors of DNA repair, 10(-3) M caffeine and 5 x 10(-6) M 1-beta-D-arabinofuranosylcytosine, was also tested by adding 3 micrograms/ml ellipticine at G2 in 30-min pulses and immediately followed by caffeine and/or ara-C during the last 3 h before harvesting. Three experiments performed on blood from 3 donors showed a moderate potentiation effect on the frequency of chromatid-type aberrations (about 2-3 times) by both inhibitors. Likewise, a 3-fold increase was observed in the frequencies of chromosomal aberrations when caffeine and ara-C were combined. The present data demonstrate that posttreatment with caffeine and ara-C at G2 can modify the response of human lymphocytes treated with ellipticine by increasing the clastogenic action of this compound or by changing the cell-cycle progression.     

In vitro sensitization of human lymphocytes to a myeloma cell-related antigen

Peripheral blood lymphocytes from normal human donors were cocultivated with cells from two established human multiple myeloma cell lines, RPMI 8226 and K-737, and with lymphoblastoid cells from a third B cell line, RAMM. After a comparison of three methods of lymphocyte sensitization, a 6-day incubation protocol with equal numbers of normal lymphocytes and mitomycin C-treated tumor cells was selected. Cells from the RPMI 8226 myeloma line stimulated the differentiation of lymphocytes into cytotoxic effector cells as measured by ⁵¹Cr release from labeled target cells. The RPMI 8226-sensitized lymphocytes were cytotoxic for myeloma cells (RPMI 8226 and K-737) and for lymphoblastoid cells (RAMM) but not for cells from human lung tumor lines (A549, A427, MB9812), a breast carcinoma line (ALAB), a normal diploid fibroblast line (HSBP), or normal lymphocytes.     

MLC-specific suppressor T lymphocytes in man. I. Their induction in vitro by soluble HLA-DR antigens

Human T lymphocytes precultured for 36 hr in the presence of soluble HLA-DR antigens suppress the MLR response of autologous peripheral blood lymphocytes to allogeneic stimulating cells. The suppression is DR antigen-specific in that it appears that the MLR stimulating cell donor and the soluble suppressor-inducing antigen must share DR specificities. The soluble DR antigens were fractionated from the sera of normal donors using QAE-Sephadex chromatography and CNBr-activated Sepharose immunoadsorption. Similarly prepared HLA-A and -B antigens failed to induce suppressive activity. The suppressive activity of DR-antigen cultured T cells is resistant to mitomycin C treatment and, further, the antigen specificity is maintained with or without mitomycin C treatment. The kinetics of suppressor cell induction as well as the kinetics of suppression in the test MLR cultures are presented. The implications of these results are discussed.     

Neonatal susceptibility to MHV3 infection in mice. II. Role of natural effector marrow cells in transfer of resistance

Protection of newborn mice against MHV3 infection requires the transfer of several cell populations originating from adult syngeneic donors: adherent spleen cells, T lymphocytes, and a third population present in the nonadherent spleen cell fraction, in peritoneal exudates, and in bone marrow cells (M cells). M cells were found to be sensitive to short-term incubation at 37 degrees C and to preincubation with anti-bone marrow antiserum, mitomycin C, puromycin, and aggregated Ig, the latter suggesting the presence of Fc receptors. They were resistant to silica particles but were sensitive to irradiation with x-rays as well as with 89Strontium. Nonadherent spleen cells, however, behaved differently from M cells toward x-irradiation since they were radio-resistant, suggesting that M cells are precursors that require further differentiation or division to participate in MHV3 resistance. Effector M cells responsible for MHV3 resistance display, therefore, some similarities with natural killing cells. They might belong to a group of effector cells operative in regulatory processes or anti-tumor surveillance but also may be defense mechanisms against infectious diseases.     

Application of orthogonal light scattering for routine screening of lymphocyte samples

Orthogonal and forward light-scattering properties of lymphocytes were measured from patients with different lymphocytic diseases in order to determine the potential value of light scattering as a screening device. Monitoring of orthogonal light scattering of lymphocytes of a B-cell chronic lymphocytic leukemia patient during splenic irradiation (SI) revealed the selective decrease of malignant cells and the fact that the major part of the residual lymphocytes were cytotoxic lymphocytes. By combining forward and orthogonal light scattering it was shown that lymphocytes from a patient with T gamma lymphocytosis were abnormal. Orthogonal light scattering also showed an increase in cytotoxic lymphocytes in a patient with mononucleosis infectiosa and in a splenectomized patient. Orthogonal light scattering of lymphocyte subpopulations showed that the leu8+ population of a patient with mononucleosis infectiosa was bidisperse. For elderly donors the occurrence of CD3+, CD4+, CD8+, and HNK-1+ lymphocytes with a large orthogonal light scattering varied considerably. The CD8+ lymphocytes of these donors consisted mainly of cytotoxic lymphocytes. These results show that determination of light-scattering properties of lymphocytes may yield important diagnostic information and can indicate when further investigation of the lymphocytes by means of immunofluorescence is necessary.     

UV-C sensitivity of unstimulated and stimulated human lymphocytes from normal and xeroderma pigmentosum donors in the comet assay: a potential diagnostic technique.

We have studied incision-break formation in unstimulated and stimulated populations of human T-lymphocytes using the comet (single-cell microgel electrophoresis) assay. The frequency of strand breaks 1 h after UV-irradiation appears to be far greater in unstimulated than in stimulated lymphocytes from normal donors and the excess of strand breaks was observed for a far longer time after irradiation. This result corroborates the greater sensitivity of UV-C irradiation observed in a colony-forming assay but suggests that the defect may relate to a defect in strand rejoining rather than a defect in incision. Few strand breaks were seen in either unstimulated or stimulated lymphocytes of four xeroderma pigmentosum donors, suggesting that the method may offer a rapid diagnostic assay for XP.     

Age-related increase of mitomycin C-induced micronuclei in lymphocytes from Down's syndrome subjects

Peripheral blood lymphocytes from 7 patients with Down's syndrome (DS; trisomy 21) and 14 healthy age-matched controls were studied for the induction of micronuclei (MN) by the cytokinesis-block method. The spontaneous incidence of MN in lymphocytes from DS subjects was lower than that of control cultures. When lymphocytes were treated with mitomycin C (MMC) at the beginning of the culture period, an increase in MN formation was found in cells from both DS and control subjects. In DS subjects this increase was much more marked than in control donors. This effect had to be ascribed to cells from older DS subjects (37-55 years old), which showed an MMC-induced MN formation that was markedly and significantly higher than that observed in cells from younger (9-16 years old) DS subjects. These data indicate that age has to be considered a major variable when studies on the genetic instability of DS subjects are performed.     

Cytogenetic and survival adaptive responses in G1 phase human lymphocytes.

Human lymphocytes from six donors were treated with 5 cGy of X-rays followed by 200 or 400 cGy in the first G1 phase after PHA stimulation, and assayed for cytogenetic aberrations and cell survival. Four donors showed cytogenetic adaptive responses with 400 cGy, and one with both 200 cGy and 400 cGy. Both exchanges and deletions were reduced, indicating that the cytogenetic adaptive response acts by restitution of chromosome breaks. Good correlations were found between nonaberrant cells and survival, although the former were often higher than the later, especially with the 400 cGy dose. In four of six donors, 5 cGy alone had significant effects on cell survival; however, this was independent of the 5 cGy effect on high-dose-induced responses. Two donors had survival adaptive responses with 5 + 200 cGy, while none were found with the 5 + 400 cGy treatment. The comparisons between the cytogenetic and survival responses suggests that a survival adaptive response will only be seen with a sufficient increase in nonaberrant cells. To date, adaptive responses to ionizing radiation have been reported to occur in G0, G1 and late S/early G2 human lymphocytes.     

Generation of natural killer-like activity in mixed lymphocyte-tumor cell cultures. I. Role of HLA-DR antigens as stimulatory molecules

A number of human lymphoid and non-lymphoid leukemic cell lines differing for expression of HLA-DR antigens were analyzed for the ability to induce natural killer(NK)-like activity and proliferation in lymphocytes from healthy donors. The ability to elicit the generation of NK-like activity in the responder lymphocytes varied greatly depending upon the type of antimitotic treatment (gamma-irradiation versus mitomycin C) received by the tumor cells prior to the start of the mixed cultures. By contrast, the induction of T-cell proliferation was positively correlated with the presence of DR molecules on the tumor cell lines. Nevertheless, DR- leukemic cells pretreated with the appropriate antimitotic agent did induce a proliferative response in the mixed cultures. T lymphocytes cultured without stimulator cells in spent medium containing high levels of cell-free DR antigens failed to undergo blastogenesis and proliferation, indicating that DR antigens can function as stimulatory molecules only when they are cell-associated.     

Exposure to radiofrequency radiation (900 MHz, GSM signal) does not affect micronucleus frequency and cell proliferation in human peripheral blood lymphocytes: an interlaboratory study

The objective of this study was to investigate whether 24 h exposure to radiofrequency electromagnetic fields similar to those emitted by mobile phones induces genotoxic effects and/or effects on cell cycle kinetics in cultured human peripheral blood lymphocytes. The effect of 900 MHz exposure (GSM signal) was evaluated at four specific absorption rates (SARs, 0, 1, 5 and 10 W/kg peak values). The exposures were carried out in wire patch cells under strictly controlled conditions of both temperature and dosimetry, and the induction of genotoxic effects was evaluated in lymphocyte cultures from 10 healthy donors by applying the cytokinesis-block micronucleus assay. Positive controls were provided by using mitomycin C. Two research groups were involved in the study, one at ENEA, Rome, and the other at CNR-IREA, Naples. Each laboratory tested five donors, and the resulting slides were scored by both laboratories. Following this experimental scheme, it was also possible to compare the results obtained by cross-scoring of slides. The results obtained provided no evidence for the existence of genotoxic or cytotoxic effects in the range of SARs investigated. These findings were confirmed in the two groups of five donors examined in the two laboratories and when the same slides were scored by two operators.     

Banding technique used for the detection of chromosomal aberrations induced by radiation and alkylating agents TEPA and epichlorohydrin.

Blood samples from two healthy donors were exposed, (1) to 200 R of X-rays in G0 and G1S phases of the cell cycle, and (2) to epichlorohydrin 10(-6) M and TEPA 10(-4) M in G0 and/or in G1S and G2 phases. Part of the cells was processed for chromosome studies conventionally and the other part by the trypsinization banding technique. Detailed chromosomal analysis showed that, after irradiation, 38.2% of aberrations in G0 and 18.7% in G1S phases escaped cytogenetic detection when the conventional technique was used. After exposures to TEPA and ECHH, 10.9% of aberrations were undectable in G0 and 3.3% in G1S and G2 phases. The distribution of chromosome breaks was non-random both after irradiation and after exposure to alkylating agents. However, it differed according to the mutagen used. Some chromosomal segments were broken significantly more frequently than the others (e.g. 9q12), some were resistant to breakage (e.g. the whole Y chromsome). The segments represented by G-negative bands were more fragile than the G-positive and G-variable segments.     

NMR and computational characterization of mitomycin cross-linked to adjacent deoxyguanosines in the minor groove of the d(T-A-C-G-T-A).d(T-A-C-G-T-A) duplex

Two-dimensional homonuclear and heteronuclear NMR and minimized potential energy calculations have been combined to define the structure of the antitumor agent mitomycin C (MC) cross-linked to deoxyguanosines on adjacent base pairs in the d(T1-A2-C3-G4-T5-A6).d(T7-A8-C9-G10-T11-A12) duplex. The majority of the mitomycin and nucleic acid protons in the MC-X 6-mer complex have been assigned from through-bond and through-space two-dimensional proton NMR studies in aqueous solution at 5 and 20 degrees C. The C3.G10 and G4.C9 base pairs are intact at the cross-link site and stack on each other in the complex. The amino protons of G4 and G10 resonate at 9.36 and 8.87 ppm and exhibit slow exchange with solvent H2O. The NMR experimental data establish that the mitomycin is cross-linked to the DNA through the amino groups of G4 and G10 and is positioned in the minor groove. The conformation of the cross-link site is defined by a set of NOEs between the mitomycin H1" and H2" protons and the nucleic acid imino and amino protons of G4 and the H2 proton of A8 and another set of NOEs between the mitomycin geminal H10" protons and the nucleic acid imino and amino protons of G10 and the H2 proton of A2. Several phosphorus resonances of the d(T-A-C-G-T-A) duplex shift dramatically on mitomycin cross-link formation and have been assigned from proton-detected phosphorus-proton two-dimensional correlation experiments. The proton chemical shifts and NOEs establish fraying at the ends of the d(T-A-C-G-T-A) duplex, and this feature is retained on mitomycin cross-link formation. The base-base and base-sugar NOEs exhibit similar patterns for symmetry-related steps on the two nucleic acid strands in the MC-X 6-mer complex, while the proton and phosphorus chemical shifts are dramatically perturbed at the G10-T11 step on cross-link formation. The NMR distance constraints have been included in minimized potential energy computations on the MC-X 6-mer complex. These computations were undertaken with the nonplanar five-membered ring of mitomycin in each of two pucker orientations. The resulting low-energy structures MX1 and MX2 have the mitomycin cross-linked in a widened minor groove with the chromophore ring system in the vicinity of the G10-T11 step on one of the two strands in the duplex.(ABSTRACT TRUNCATED AT 400 WORDS)     

In vitro induction of HLA-restricted cytotoxic T lymphocytes against autologous Epstein-Barr Virus transformed B lymphoblastoid cell line

Cytotoxic T lymphocytes (CTL) against autologous EBV-transformed B lymphoblastoid cell line (LCL) were induced in vitro by culturing peripheral blood lymphocytes (PBL) of healthy donors together with mitomycin C-treated autologous LCL for 6 days. The cytotoxic cells developed only from the E-rosette-positive fraction but not from the negative fraction of PBL. These CTL killed autologous LCL but not PWM-stimulated autologous PBL. In addition, the CTL killed allogeneic LCL when at least 1 of the HLA-A antigens was identical with that of the LCL of CTL donor. However, identity of HLA-B and HLA-C antigens was not enough for a significant killing of allogeneic LCL. The specificity of the CTL was also confirmed by a cold target inhibition test. These results indicated that the CTL induced specifically recognized EBV-transformed cells with HLA restriction.     

Immunodominant T-cell epitope on the F protein of respiratory syncytial virus recognized by human lymphocytes.

The lymphocyte proliferative responses to respiratory syncytial virus (RSV) were evaluated for 10 healthy adult donors and compared with proliferative responses to a chimeric glycoprotein (FG glycoprotein) which consists of the extracellular domains of both the F and G proteins of RSV and which is produced from a recombinant baculovirus. The lymphocytes of all 10 donors responded to RSV, and the proliferative responses to the whole virus were highly correlated with the responses to the FG glycoprotein. These data suggested that one or both of these glycoproteins of RSV were major target structures for stimulation of the human lymphocyte proliferative response among virus-specific memory T cells. The lymphocytes of four donors were evaluated further for their proliferative responses to a nested set of overlapping peptides modeled on the extracellular and cytoplasmic domains of the F protein of RSV. Strikingly, the lymphocytes of all 4 donors responded primarily to a region defined by a single peptide spanning residues 338 to 355, and the lymphocytes of 2 donors responded to an overlapping peptide spanning residues 328 to 342 also, thus defining a region of the F1 subunit within residues 328 to 355 that may circumscribe an immunodominant site for stimulation of human T cells from a variety of individuals. This region of the F protein is highly conserved among A and B subgroup viruses. As revealed by monoclonal antibody blocking studies, the lymphocytes responding to this antigenic site had characteristics consistent with T helper cells. Similar epitope mapping studies were performed with BALB/c mice immunized with the FG protein in which a relatively hydrophobic peptide spanning residues 51 to 65 within the F2 subunit appeared to be the major T cell recognition determinant. The data are discussed with respect to an antigenic map of the F protein and the potential construction of a synthetic vaccine for RSV.