597 research outputs found
Role of CD28/B7 costimulation and IL-12/IL-10 interaction in the radiation-induced immune changes
BACKGROUND: The present paper aims at studying the role of B7/CD28 interaction and related cytokine production in the immunological changes after exposure to different doses of ionizing radiation. RESULTS: The stimulatory effect of low dose radiation (LDR) on the proliferative response of lymphocytes to Con A was found to require the presence of APCs. The addition of APCs obtained from both low- and high-dose-irradiated mice to splenic lymphocytes separated from low-dose-irradiated mice caused stimulation of lymphocyte proliferation. B7-1/2 expression on APCs was up-regulated after both low and high doses of radiation. There was up-regulation of CD28 expression on splenic and thymic lymphocytes after LDR and its suppression after high dose radiation (HDR), and cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) expression showed changes in the opposite direction. IL-12 secretion by macrophages was stimulated after both low and high doses of radiation, but IL-10 synthesis by splenocytes was suppressed by low dose radiation and up-regulated by high dose radiation. CONCLUSION: The status of CD28/CTLA-4 expression on T lymphocytes in the presence of up-regulated B7 expression on APCs determined the outcome of the immune changes in response to radiation, i.e., up-regulation of CD28 after LDR resulted in immunoenhancement, and up-regulation of CTLA-4 associated with down-regulation of CD28 after HDR led to immunosuppression. Both low and high doses of radiation up-regulated B7-1/2 expression on APCs. After LDR, the stimulated proliferative effect of increased IL-12 secretion by APCs, reinforced by the suppressed secretion of IL-10, further strengthened the intracellular signaling induced by B7-CD28 interaction
Entrance channel dependence and isospin dependence of preequilibrium nucleon emission in intermediate energy heavy ion collisions
Using isospin dependent quantum molecular dynamical model, the studies of the
isospin effect on preequilibrium nucleon emission in heavy ion collisions under
different entrance channel conditions show that the ratio of preequilibrium
neutron number to proton number depends strongly on symmetry potential, beam
energy, and the ratio of neutron to proton of the colliding system, but weakly
on isospin dependent in-medium nucleon-nucleon cross sections, impact
parameter, Pauli potential, and momentum dependent interaction in the energy
region from 45MeV/u up to 150 MeV/u where the dynamics is dominated by
nucleon-nucleon collisions. In addition, the ratio of preequilibrium neutron
number to proton number for a neutron-rich colliding system is larger than the
initial value of the ratio of the colliding system, but the ratio for a
neutron-deficient system is less than the initial value
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