Molecular and cellular profiling of acute responses to total body radiation exposure in ovariectomized female cynomolgus macaques

Abstract

Purpose: The threat of radiation exposure requires a mechanistic understanding of radiation-induced immune injury and recovery. The study objective was to evaluate responses to ionizing radiation in ovariectomized (surgically post-menopausal) female cynomolgus macaques.

Materials and methods: Animals received a single total-body irradiation (TBI) exposure at doses of 0, 2 or 5 Gy with scheduled necropsies at 5 days, 8 weeks and 24 weeks post-exposure. Blood and lymphoid tissues were evaluated for morphologic, cellular, and molecular responses.

Results: Irradiated animals developed symptoms of acute hematopoietic syndrome, and reductions in thymus weight, thymopoiesis, and bone marrow cellularity. Acute, transient increases in plasma monocyte chemoattractant protein 1 (MCP-1) were observed in 5 Gy animals along with dose-dependent alterations in messenger ribonucleic acid (mRNA) signatures in thymus, spleen, and lymph node. Expression of T cell markers was lower in thymus and spleen, while expression of macrophage marker CD68 (cluster of differentiation 68) was relatively elevated in lymphoid tissues from irradiated animals.

Conclusions: Ovariectomized female macaques exposed to moderate doses of radiation experienced increased morbidity, including acute, dose-dependent alterations in systemic and tissue-specific biomarkers, and increased macrophage/T cell ratios. The effects on mortality exceeded expectations based on previous studies in males, warranting further investigation.

Keywords: Radiation; acute effects; cytokines; immunology; macrophage; molecular profiling; non-human primate; total body irradiation.

Figure 1

Effects of 2 and 5 Gy TBI on circulating blood components: (A) Platelets, (B) Neutrophils, (C) Lymphocytes, and (D) Erythrocytes. Single data points from individuals plotted across time. This Figure is reproduced in color in the online version of International Journal of Radiation Biology

Figure 2

Histologic sections of bone marrow (A–C) and spleen (D–F) from a control animal (0 Gy, A and D) and irradiated animals (2 Gy, B and E; and 5 Gy, C and F) five days post radiation exposure. The bone marrow from the irradiated animals was severely hypocellular with necrosis and loss of cells across all hematopoietic lineages. Note the dose-dependent marked necrosis and depletion of lymphoid follicles in the spleens of irradiated animals. Hematoxylin and eosin stain. Magnification 2×; inset magnification; 40×. Areas of splenic white pulp are marked with an (*). This Figure is reproduced in color in the online version of International Journal of Radiation Biology

Figure 3

Effects of 2 and 5 Gy TBI on thymus weight (A), thymic sjTREC levels, (B) and thymic histology (C). Data are mean ± SEM of n = 3–6 per group. Data from samples from each dose at different post-irradiation time-points were pooled for analysis due to the low number of observations and the lack of evidence for a time dependent trend. In the 0 and 5 Gy histologic sections note the marked loss of architecture (almost complete loss of cortical lymphocytes), with relative sparing of medullary epithelial elements, in the thymus from the animal treated with 5 Gy (right panels), compared to an un-irradiated control (left panels). Hematoxylin and eosin stain. Upper panels 4×, lower panels 20×. This Figure is reproduced in color in the online version of International Journal of Radiation Biology

Figure 4

Effects of 2 and 5 Gy TBI on levels of mRNA for T cell (CD3) and macrophage (CD68) markers as indices of tissue cell populations in lymph node, spleen, and thymus. Data from samples from each dose at different post-irradiation time-points were pooled for analysis due to the low number of observations and the lack of evidence for a time-dependent trend. Error bars indicate the standard error of the mean (SEM) for n = 3–6 per group. This Figure is reproduced in color in the online version of International Journal of Radiation Biology

Figure 5

Effects of 2, and 5 Gy TBI on plasma MCP-1. Single data points from individuals plotted across time. This Figure is reproduced in color in the online version of International Journal of Radiation Biology