Sensitivity of porcine peripheral blood leukocytes to gamma irradiation in vivo, in vitro and ex vivo

MITOCHONDRIA IN BIODOSIMETRY: FLOW CYTOMETRY ASSESMENT IN VITRO

The JC-1 dye is widely used in apoptosis studies to monitor mitochondrial health. The probe was tested in vitro on two established cell lines and peripheral porcine blood lymphocytes after gamma irradiation (IR) to assess its potential in biodosimetric evaluation. In brief, we stained irradiated and non-irradiated cells with the JC-1 dye to determine the existing changes in mitochondrial membrane potential and monitor cell health through flow cytometry. The stage of injury in these cells was evaluated through an irradiated versus non-irradiated ratio (IVNIR), comparing the relative proportion of polarised cells containing red JC-1 aggregates. We observed a decreasing IVNIR as the radiation dose increased (i.e. 0.5; 1; 2; 4; 6; 8 and 10 Gy), performing the analysis at 4, 8 and 24 h after IR in all the tested cells. The results from the JC1-dye test showed that CD4 T lymphocytes were more sensitive to irradiation than other subpopulations.

NEW EXPERIMENTAL APPROACH IN BIODOSIMETRY: EX VIVO APOPTOSIS DETECTION

This study establishes a new experimental approach for retrospective biodosimetric assessment by apoptosis detection ex vivo. For this purpose, we used mononuclear blood leukocytes isolated from the peripheral blood of irradiated Wistar rats and cultured them ex vivo for posterior analysis. Using flow cytometry, we distinguished apoptotic lymphocyte subsets individual biodosimetric potential at different time periods after exposure: B-lymphocytes 6-8 h (0-7 Gy), natural killer cells 24 h (0-7 Gy) and T-lymphocytes 24 h (0-1 Gy). This novel experimental design innovates through the need of a single blood sample from irradiated individuals for a complete biodosimetric assessment.

Predictive factors of cytotoxic damage in radioactive iodine treatment of differentiated thyroid cancer patients

Radioactive iodine (¹³¹I) therapy in patients suffering from differentiated thyroid cancer (DTC) is a targeted treatment commonly used for thyroid ablation and locoregional and distant metastatic spread management. Despite a significant proportion of the ¹³¹I dose entering the circulation, there is currently no detailed information regarding its effect on the blood cell system. In order to assess the cytotoxic effects of ¹³¹I therapy on the circulatory system, blood cell levels, thyroid-related hormones and CD45⁺ cell cytotoxicity were estimated in blood collected from patients with DTC. The micronuclei (MN) frequency of the peripheral blood CD45⁺ cell fraction was significantly increased after 30 days of ¹³¹I therapy compared to that prior to treatment, although a strong individual variation was observed. A significantly negative correlation between MN frequency and the level of platelets and plateletcrit was observed; however, there was no such correlation with thyroid-related hormones. These resultS suggest that the correlation between MN frequency and the platelet system may serve as a biomarker of exposure and, possibly, of sensitivity in DTC patients undergoing ¹³¹I therapy following thyroid and lymph node surgery.

Lymphocyte subsets and their H2AX phosphorylation in response to in vivo irradiation in rats

PURPOSE

The objective of the study was to investigate differences in the radiosensitivity of rat peripheral blood lymphocyte subsets identified by expression of surface clusters of differentiation markers (CD3, CD4, CD8, CD45RA, CD161) after whole-body in vivo gamma-ray irradiation and to assess their individual histone H2AX phosphorylation as an early cell response to irradiation.

MATERIALS AND METHODS

The relative representations of CD45RA B-lymphocytes, CD161 natural killer cells (NK cells), CD3CD4 T-lymphocyte subset and CD3CD8 T-lymphocyte subset in the rat peripheral blood were studied 24-72 hours after irradiation in a dose range of 0-5 Gy. Their intracellular H2AX phosphorylation (γ-H2AX) after 4 Gy and 9 Gy whole-body in vivo irradiation was assessed by multicolour flow cytometry.

RESULTS

We determined the linear dose response of radioresistant CD161 NK cells (24 h), both radiosensitive T-lymphocyte subsets (24 h) and CD45RA B-lymphocytes (72 h) after in vivo irradiation. CD45RA B-lymphocytes showed the highest radiosensitivity and we observed pronounced H2AX phosphorylation which remained expressed in these cells for over 4 h after irradiation.

CONCLUSION

The combination of the surface immunophenotyping together with intracellular detection of γ-H2AX offers the possibility to assess the absorbed dose of ionizing irradiation with high sensitivity post irradiation and could be successfully applied to biodosimetry.

Attempted depletion of passenger leukocytes by irradiation in pigs

Allograft/xenograft rejection is associated with “passenger leukocyte” migration from the organ into recipient lymph nodes. In Study 1, we attempted to deplete leukocytes from potential kidney “donor” pigs, using two regimens of total body irradiation. A dose of 700 cGy was administered, followed by either 800 cGy (“low-dose”) or 1,300 cGy (“high dose”) with the kidneys shielded. Neither regimen was entirely successful in depleting all leukocytes, although remaining T and 8 cell numbers were negligible. Study 2 was aimed at providing an indication of whether near-complete depletion of leukocytes had any major impact on kidney allograft survival. In non-immunosuppressed recipient pigs, survival of a kidney from a donor that received high-dose irradiation was compared with that of a kidney taken from a non-irradiated donor. Kidney graft survival was 9 and 7 days, respectively, suggesting that depletion had little impact on graft survival. The lack of effect may have been related to (i) inadequate depletion of passenger leukocytes, thus not preventing a direct T cell response, (ii) the presence of dead or dying leukocytes (antigens), thus not preventing an indirect T cell response, or (iii) constitutive expression of MHC class II and B7 molecules on the porcine vascular endothelium, activating recipient T cells.