Effects of in Vivo Proton Irradiation on Mouse T and B Lymphocytes

Abstract

Abstract. One of the major problems derived from the exposure to ionizing radiation is the impairment of the immune system. The consequent immune-depression increases the risk of infections and may lead to immunemediated disorders. The intensity and duration of the immune-compromised phase and its recovery depend on the dose, dose-rate and quality of radiation. In recent years, there has been a great interest in the effects induced by protons, both for a better assessment of the health risks in astronauts exposed to solar wind and cosmic radiations and for a better understanding of their effects in radiotherapy for oncologic patients. In the present study, we investigated the effects of the in vivo exposure to 2 Gy of integral dose absorbed by medium energy proton beams on mouse lymphoid spleen cells. The TOP-IMPLART accelerator was used as proton source. Irradiations were performed in air with pulsed (3.4 s, 10Hz) 27 MeV proton beams. During the exposure, mice were anesthetized in order to keep them in the right position. Sham-exposed anesthetized age/gender/strain-matched mice were used as controls. Twenty-four hours and 1 week after irradiation, each mouse was individually analyzed for several parameters (5 mice/group). Results showed that the number of nucleated cells in the spleen was not significantly affected. Flow cytometry analyses revealed that the percentages of helper T (CD4), cytotoxic T (CD8) and B (CD19) cells within the spleen lymphocytes were not altered 24 hours after the exposure. At variance, 1 week after the exposure the frequency of CD4 (14% vs. 9%) and CD19 (37% vs. 26%) cells reduced. Spleen cells were stimulated with an anti-CD3 antibody and LPS to induce T cell and B cell activation, respectively. Both T and B cells were functionally impaired by the exposure. Twenty-four hours after irradiation, T cell proliferation was indeed reduced by 50% in exposed mice compared with controls. B cells also displayed a reduced cell proliferation in response to the mitogenic stimulus (-33%). Interestingly, 1 week after irradiation proliferative responses of T and B cells were still compromised. This first study allowed the conclusion that, in vivo local exposure to protons induced small changes in total spleen cell number, the frequency of CD4 and B cells being reduced 1 week after the exposure. More interesting, functional responses, such as T and B cell proliferation were partially compromised. These effects, in spite of the limited area of exposure, were not recovered after 1 week.

Irradiation Activity With the Top-Implart Proton Linear Accelerator

“…The second block of irradiation is located one meter from the exit window -here the beam passes through a volume of air that generates a spot-widening up to about 19 mm (rms) with a uniformity better than 95% on a circle with 10 mm diameter, then collimated as required by the specific irradiation [12]. In this point, the beam energy drops from 27 to 24 MeV, corresponding to 6 mm of penetration depth in the water.…”

“…Horizontal large -Small animals [12] -Vegetables [15] -Dosimeters tests [16] Table 2 lists the system used for beam monitoring during irradiation experiments. We focused on the ionization dosimetry using different and accurate compared methods [16]: ionization chambers (IC) measurements, EPR/Alanine dosimetry, MOSFET radiation sensor analysis, film dosimetry, semiconductor detectors and luminescent devices.…”