Molecular measurement of T cell receptor excision circles

Systemic immunostimulation induces glucocorticoid-mediated thymic involution succeeded by rebound hyperplasia which is impaired in aged recipients

The thymus is the central organ involved with T-cell development and the production of naïve T cells. During normal aging, the thymus undergoes marked involution, reducing naïve T-cell output and resulting in a predominance of long-lived memory T cells in the periphery. Outside of aging, systemic stress responses that induce corticosteroids (CS), or other insults such as radiation exposure, induce thymocyte apoptosis, resulting in a transient acute thymic involution with subsequent recovery occurring after cessation of the stimulus. Despite the increasing utilization of immunostimulatory regimens in cancer, effects on the thymus and naïve T cell output have not been well characterized. Using both mouse and human systems, the thymic effects of systemic immunostimulatory regimens, such as high dose IL-2 (HD IL-2) with or without agonistic anti-CD40 mAbs and acute primary viral infection, were investigated. These regimens produced a marked acute thymic involution in mice, which correlated with elevated serum glucocorticoid levels and a diminishment of naïve T cells in the periphery. This effect was transient and followed with a rapid thymic "rebound" effect, in which an even greater quantity of thymocytes was observed compared to controls. Similar results were observed in humans, as patients receiving HD IL-2 treatment for cancer demonstrated significantly increased cortisol levels, accompanied by decreased peripheral blood naïve T cells and reduced T-cell receptor excision circles (TRECs), a marker indicative of recent thymic emigrants. Mice adrenalectomized prior to receiving immunotherapy or viral infection demonstrated protection from this glucocorticoid-mediated thymic involution, despite experiencing a substantially higher inflammatory cytokine response and increased immunopathology. Investigation into the effects of immunostimulation on middle aged (7-12 months) and advance aged (22-24 months) mice, which had already undergone significant thymic involution and had a diminished naïve T cell population in the periphery at baseline, revealed that even further involution was incurred. Thymic rebound hyperplasia, however, only occurred in young and middle-aged recipients, while advance aged not only lacked this rebound hyperplasia, but were entirely absent of any indication of thymic restoration. This coincided with prolonged deficits in naïve T cell numbers in advanced aged recipients, further skewing the already memory dominant T cell pool. These results demonstrate that, in both mice and humans, systemic immunostimulatory cancer therapies, as well as immune challenges like subacute viral infections, have the potential to induce profound, but transient, glucocorticoid-mediated thymic involution and substantially reduced thymic output, resulting in the reduction of peripheral naive T cells. This can then be followed by a marked rebound effect with naïve T cell restoration, events that were shown not to occur in advanced-aged mice.

Comprehensive Flow Cytometric, Immunohistologic, and Molecular Assessment of Thymus Function in Rhesus Macaques

The critical importance of the thymus for generating new naive T cells that protect against novel infections and are tolerant to self-antigens has led to a recent revival of interest in monitoring thymic function in species other than humans and mice. Nonhuman primates such as rhesus macaques (Macaca mulatta) provide particularly useful animal models for translational research in immunology. In this study, we tested the performance of a 15-marker multicolor Ab panel for flow cytometric phenotyping of lymphocyte subsets directly from rhesus whole blood, with validation by thymectomy and T cell depletion. Immunohistochemical and multiplex RNA expression analysis of thymus tissue biopsies and molecular assays on PBMCs were used to further validate thymus function. Results identify Ab panels that can accurately classify rhesus naive T cells (CD3+CD45RA+CD197+ or CD3+CD28+CD95-) and recent thymic emigrants (CD8+CD28+CD95-CD103+CD197+) using just 100 µl of whole blood and commercially available fluorescent Abs. An immunohistochemical panel reactive with pan-cytokeratin (CK), CK14, CD3, Ki-67, CCL21, and TdT provides histologic evidence of thymopoiesis from formalin-fixed, paraffin-embedded thymus tissues. Identification of mRNAs characteristic of both functioning thymic epithelial cells and developing thymocytes and/or molecular detection of products of TCR gene rearrangement provide additional complementary methods to evaluate thymopoiesis, without requiring specific Abs. Combinations of multiparameter flow cytometry, immunohistochemistry, multiplex gene expression, and TCR excision circle assays can comprehensively evaluate thymus function in rhesus macaques while requiring only minimal amounts of peripheral blood or biopsied thymus tissue.

Thymus in Cardiometabolic Impairments and Atherosclerosis: Not a Silent Player?

The thymus represents a primary organ of the immune system, harboring the generation and maturation of T lymphocytes. Starting from childhood, the thymus undergoes involution, being replaced with adipose tissue, and by an advanced age nearly all the thymus parenchyma is represented by adipocytes. This decline of thymic function is associated with compromised maturation and selection of T lymphocytes, which may directly impact the development of inflammation and induce various autoinflammatory disorders, including atherosclerosis. For a long time, thymus health in adults has been ignored. The process of adipogenesis in thymus and impact of thymic fat on cardiometabolism remains a mysterious process, with many issues being still unresolved. Meanwhile, thymus functional activity has a potential to be regulated, since islets of thymopoeisis remain in adults even at an advanced age. The present review describes the intricate process of thymic adipose involution, focusing on the issues of the thymus' role in the development of atherosclerosis and metabolic health, tightly interconnected with the state of vessels. We also review the recent information on the key molecular pathways and biologically active substances that may be targeted to manipulate both thymic function and atherosclerosis.

Long-Term Immunological Consequences of Radiation Exposure in a Diverse Cohort of Rhesus Macaques

PURPOSE

The aim of this study was to develop an improved understanding of the delayed immunologic effects of acute total body irradiation (TBI) using a diverse cohort of nonhuman primates as a model for an irradiated human population.

METHODS AND MATERIALS

Immune recovery was evaluated in 221 rhesus macaques either left unirradiated (n = 36) or previously irradiated (n = 185) at 1.1 to 8.5 Gy TBI (median, 6.5 Gy) when aged 2.1 to 15.5 years (median, 4.2 years). Blood was drawn annually for up to 5 years total between 0.5 and 14.3 years after exposure. Blood was analyzed by complete blood count, immunophenotyping of monocytes, dendritic cells (DC) and lymphocytes by flow cytometry, and signal joint T-cell receptor exclusion circle quantification in isolated peripheral blood CD4 and CD8 T cells. Animals were categorized by age, irradiation status, and time since irradiation. Sex-adjusted means of immune metrics were evaluated by generalized estimating equation models to identify cell populations altered by TBI.

RESULTS

Overall, the differences between irradiated and nonirradiated animals were subtle and largely restricted to younger animals and select cell populations. Subsets of monocytes, DC, T cells, and B cells showed significant interaction effects between radiation dose and age after adjustment for sex. Irradiation at a young age caused transient increases in the percentage of peripheral blood myeloid DC and dose-dependent changes in monocyte balance for at least 5 years after TBI. TBI also led to a sustained decrease in the percentage of circulating memory B cells. Young irradiated animals exhibited statistically significant and prolonged disruption of the naïve/effector memory/central memory CD4 and CD8 T-cell equilibrium and exhibited a dose-dependent increase in thymopoiesis for 2 to 3 years after exposure.

CONCLUSIONS

This study indicates TBI subtly but significantly alters the circulating proportions of cellular mediators of adaptive immune memory for several years after irradiation, especially in macaques under 5 years of age and those receiving a high dose of radiation.

Monitoring T-Cell Kinetics in the Early Recovery Period of Lung Transplantation Cases by Copy Number Levels of T-Cell Receptor Excision Circle

BACKGROUND/AIM

Lung transplantation is a life-saving procedure for patients with end-stage lung diseases. T-Cell receptor excision circle (TREC) is circular DNA produced during T-cell receptor gene rearrangement in the thymus and indicates naive T-cell migration from the thymus. Therefore, its levels represent thymic T-cell output. Post-transplant lymphocyte kinetics correlate with graft tolerance. The aim of this study was to investigate T-lymphocyte kinetics in the early recovery period after lung transplantation. For this purpose, copy numbers of TREC were determined in patients with a lung transplant. In addition, TREC copy numbers were evaluated according to age, diagnosis and the forced expiratory volume in 1 second (FEV1) of lung transplant patients.

MATERIALS AND METHODS

Peripheral blood samples were taken from patients aged 23 to 59 years who underwent lung transplantation at the Thoracic Surgery Clinic, Kartal-Koşuyolu High Specialization Educational and Research Hospital. This study included peripheral blood samples from 11 lung transplant patients (comprising four with chronic obstructive pulmonary disease, three with idiopathic pulmonary fibrosis, one with cystic fibrosis, one with silicosis and two with bronchiectasis; three females in total). Samples were taken at three different timepoints: Before transplant, and 24 hours and 7 days post transplant. TREC copy numbers were analyzed with real time reverse transcriptase-polymerase chain reaction.

RESULTS

Post-transplant TREC numbers and density values were higher compared to pre-transplant values, although these differences were statistically insignificant. TREC copy numbers were found to be significantly higher in patients younger than 45 years compared to patients older than 45 years. At 24 hours after the transplant, the average TREC copy number/peripheral blood mononuclear cells of the cases with an FEV1 value of or below 50% was found to be statistically significantly higher than that of cases with an FEV1 value above 50% (p=0.046). There was no statistically significant difference in TREC copy numbers between male and female patients or by diagnostic group.

CONCLUSION

TREC copy numbers can be evaluated as a prognostic marker for lung transplantation. There is a need for multicenter studies with more patients.

Long-Term Recovery of the Adaptive Immune System in Rhesus Macaques After Total Body Irradiation

PURPOSE

Ionizing radiation causes acute damage to hematopoietic and immune cells, but the long-term immunologic consequences of irradiation are poorly understood. We therefore performed a prospective study of the delayed immune effects of radiation using a rhesus macaque model.

METHODS AND MATERIALS

Ten macaques received 4 Gy high-energy x-ray total body irradiation (TBI) and 6 control animals received sham irradiation. TBI caused transient lymphopenia that resolved over several weeks. Once white blood cell counts recovered, flow cytometry was used to immunophenotype the circulating adaptive immune cell populations 4, 9, and 21 months after TBI. Data were fit using a mixed-effects model to determine age-dependent, radiation-dependent, and interacting effects. T cell receptor (TCR) sequencing and quantification of TCR Excision Circles were used to determine relative contributions of thymopoiesis and peripheral expansion to T cell repopulation. Two years after TBI, the cohort was vaccinated with a 23-valent pneumococcal polysaccharide vaccine and a tetravalent influenza hemagglutinin vaccine.

RESULTS

Aging, but not TBI, led to significant changes in the frequencies of dendritic cells, CD4 and CD8 T cells, and B cells. However, irradiated animals exhibited increased frequencies of central memory T cells and decreased frequencies of naïve T cells. These consequences of irradiation were time-dependent and more prolonged in the CD8 T cell population. Irradiation led to transient increases in CD8+ T cell TCR Excision Circles and had no significant effect on TCR sequence entropy, indicating T cell recovery was partially mediated by thymopoiesis. Animals that were irradiated and then vaccinated showed normal immunoglobulin G binding and influenza neutralization titers in response to the 4 protein antigens but weaker immunoglobulin G binding titers to 10 of the 23 polysaccharide antigens.

CONCLUSIONS

These findings indicate that TBI causes subtle but long-lasting immune defects that are evident years after recovery from lymphopenia.

Relationship between CD4 T cell turnover, cellular differentiation and HIV persistence during ART

The precise role of CD4 T cell turnover in maintaining HIV persistence during antiretroviral therapy (ART) has not yet been well characterized. In resting CD4 T cell subpopulations from 24 HIV-infected ART-suppressed and 6 HIV-uninfected individuals, we directly measured cellular turnover by heavy water labeling, HIV reservoir size by integrated HIV-DNA (intDNA) and cell-associated HIV-RNA (caRNA), and HIV reservoir clonality by proviral integration site sequencing. Compared to HIV-negatives, ART-suppressed individuals had similar fractional replacement rates in all subpopulations, but lower absolute proliferation rates of all subpopulations other than effector memory (TEM) cells, and lower plasma IL-7 levels (p = 0.0004). Median CD4 T cell half-lives decreased with cell differentiation from naïve to TEM cells (3 years to 3 months, p<0.001). TEM had the fastest replacement rates, were most highly enriched for intDNA and caRNA, and contained the most clonal proviral expansion. Clonal proviruses detected in less mature subpopulations were more expanded in TEM, suggesting that they were maintained through cell differentiation. Earlier ART initiation was associated with lower levels of intDNA, caRNA and fractional replacement rates. In conclusion, circulating integrated HIV proviruses appear to be maintained both by slow turnover of immature CD4 subpopulations, and by clonal expansion as well as cell differentiation into effector cells with faster replacement rates.

The immune system in infants: Relevance to xenotransplantation

Despite the improvement in surgical interventions in the treatment of congenital heart disease, many life-threatening lesions (eg, hypoplastic left heart syndrome) ultimately require transplantation. However, there is a great limitation in the availability of deceased human cardiac donors of a suitable size. Hearts from genetically engineered pigs may provide an alternative source. The relatively immature immune system in infants (eg, absence of anti-carbohydrate antibodies, reduced complement activation, reduced innate immune cell activity) should minimize the risk of early antibody-mediated rejection of a pig graft. Additionally, recipient thymectomy, performed almost routinely as a preliminary to orthotopic heart transplantation in this age-group, impairs the T-cell response. Because of the increasing availability of genetically engineered pigs (eg, triple-knockout pigs that do not express any of the three known carbohydrate antigens against which humans have natural antibodies) and the ability to diagnose congenital heart disease during fetal life, cardiac xenotransplantation could be preplanned to be carried out soon after birth. Because of these several advantages, prolonged graft survival and even the induction of tolerance, for example, following donor-specific pig thymus transplantation, are more likely to be achieved in infants than in adults. In this review, we summarize the factors in the infant immune system that would be advantageous in the success of cardiac xenotransplantation in this age-group.

Nucleic acid testing and molecular characterization of HIV infections

Significant advances have been made in the molecular assays used for the detection of human immunodeficiency virus (HIV), which are crucial in preventing HIV transmission and monitoring disease progression. Molecular assays for HIV diagnosis have now reached a high degree of specificity, sensitivity and reproducibility, and have less operator involvement to minimize risk of contamination. Furthermore, analyses have been developed for the characterization of host gene polymorphisms and host responses to better identify and monitor HIV-1 infections in the clinic. Currently, molecular technologies including HIV quantitative and qualitative assays are mainly based on the polymerase chain reaction (PCR), transcription-mediated amplification (TMA), nucleic acid sequence-based amplification (NASBA), and branched chain (b) DNA methods and widely used for HIV detection and characterization, such as blood screening, point-of-care testing (POCT), pediatric diagnosis, acute HIV infection (AHI), HIV drug resistance testing, antiretroviral (AR) susceptibility testing, host genome polymorphism testing, and host response analysis. This review summarizes the development and the potential utility of molecular assays used to detect and characterize HIV infections.

Late effects of total body irradiation on hematopoietic recovery and immune function in rhesus macaques

While exposure to radiation can be lifesaving in certain settings, it can also potentially result in long-lasting adverse effects, particularly to hematopoietic and immune cells. This study investigated hematopoietic recovery and immune function in rhesus macaques Cross-sectionally (at a single time point) 2 to 5 years after exposure to a single large dose (6.5 to 8.4 Gray) of total body radiation (TBI) derived from linear accelerator-derived photons (2 MeV, 80 cGy/minute) or Cobalt 60-derived gamma irradiation (60 cGy/min). Hematopoietic recovery was assessed through measurement of complete blood counts, lymphocyte subpopulation analysis, and thymus function assessment. Capacity to mount specific antibody responses against rabies, Streptococcus pneumoniae, and tetanus antigens was determined 2 years after TBI. Irradiated macaques showed increased white blood cells, decreased platelets, and decreased frequencies of peripheral blood T cells. Effects of prior radiation on production and export of new T cells by the thymus was dependent on age at the time of analysis, with evidence of interaction with radiation dose for CD8+ T cells. Irradiated and control animals mounted similar mean antibody responses to proteins from tetanus and rabies and to 10 of 11 serotype-specific pneumococcal polysaccharides. However, irradiated animals uniformly failed to make antibodies against polysaccharides from serotype 5 pneumococci, in contrast to the robust responses of non-irradiated controls. Trends toward decreased serum levels of anti-tetanus IgM and slower peak antibody responses to rabies were also observed. Taken together, these data show that dose-related changes in peripheral blood cells and immune responses to both novel and recall antigens can be detected 2 to 5 years after exposure to whole body radiation. Longer term follow-up data on this cohort and independent validation will be helpful to determine whether these changes persist or whether additional changes become evident with increasing time since radiation, particularly as animals begin to develop aging-related changes in immune function.

The Great Recession and Immune Function

The Great Recession precipitated unprecedented home foreclosures increases, but documentation of related neighborhood changes and population health is scant. Using the Detroit Neighborhood Health Study (N = 277), we examined associations between neighborhood-level recession indicators and thymic function, a life course immunological health indicator. In covariate-adjusted multilevel models, each 10 percentage point increase in abandoned home prevalence and 1 percentage point increase in 2009 home foreclosures was associated with 1.7-year and 3.3-year increases in thymic aging, respectively. Associations attenuated after adjustment for neighborhood-level social cohesion, suggesting community ties may buffer recession-related immune aging. Effects of neighborhood stressors were strongest in middle-income households, supporting theory of excess vulnerability in this group. Future research should assess whether ongoing foreclosure and blight reduction efforts improve health for residents of recession impacted neighborhoods.

The influence and impact of ageing and immunosenescence (ISC) on adaptive immunity during multiple sclerosis (MS) and the animal counterpart experimental autoimmune encephalomyelitis (EAE)

The human ageing process encompasses mechanisms that effect a decline in homeostasis with increased susceptibility to disease and the development of chronic life-threatening illness. Increasing age affects the immune system which undergoes a progressive loss of efficiency, termed immunosenescence (ISC), to impact on quantitative and functional aspects of innate and adaptive immunity. The human demyelinating disease multiple sclerosis (MS) and the corresponding animal model experimental autoimmune encephalomyelitis (EAE) are strongly governed by immunological events that primarily involve the adaptive arm of the immune response. MS and EAE are frequently characterised by a chronic pathology and a protracted disease course which thereby creates the potential for exposure to the inherent, on-going effects and consequences of ISC. Collective evidence is presented to confirm the occurrence of established and unendorsed biological markers of ISC during the development of both diseases. Moreover, results are discussed from studies during the course of MS and EAE that reveal a premature upregulation of ISC-related biomarkers which indicates untimely alterations to the adaptive immune system. The effects of ISC and a prematurely aged immune system on autoimmune-associated neurodegenerative conditions such as MS and EAE are largely unknown but current evaluation of data justifies and encourages further investigation.

Late Effects of Exposure to Ionizing Radiation and Age on Human Thymus Morphology and Function

The thymus is essential for proper development and maintenance of a T-cell repertoire that can respond to newly encountered antigens, but its function can be adversely affected by internal factors such as pregnancy and normal aging or by external stimuli such as stress, infection, chemotherapy and ionizing radiation. We have utilized a unique archive of thymus tissues, obtained from 165 individuals, exposed to the 1945 atomic bomb blast in Hiroshima, to study the long-term effects of receiving up to ∼3 Gy dose of ionizing radiation on human thymus function. A detailed morphometric analysis of thymus activity and architecture in these subjects at the time of their natural deaths was performed using bright-field immunohistochemistry and dual-color immunofluorescence and compared to a separate cohort of nonexposed control subjects. After adjusting for age-related effects, increased hallmarks of thymic involution were observed histologically in individuals exposed to either low (5-200 mGy) or moderate-to-high (>200 mGy) doses of ionizing radiation compared to unirradiated individuals (<5 mGy). Sex-related differences were seen when the analysis was restricted to individuals under 60 years of attained age at sample collection, but were not observed when comparing across the entire age range. This indicates that while females undergo slower involution than males, they ultimately attain similar phenotypes. These findings suggest that even low-dose-radiation exposure can accelerate thymic aging, with decreased thymopoiesis relative to nonexposed controls evident years after exposure. These data were used to develop a model that can predict thymic function during normal aging or in individuals therapeutically or accidentally exposed to radiation.

Dysfunction of the thymus in mice with hypertension

The aim of this study was to evaluate thymus function in mice with hypertension. A total of 60 C57BL/6J mice were randomized into control, sham surgery and two-kidney, one-clip groups (n=20 in each). At 4 or 8 weeks after surgery, mice were sacrificed, and blood, spleens, kidneys and thymuses were harvested. The results of reverse transcription-quantitative polymerase chain reaction analysis revealed that the mRNA levels of Forkhead box protein N1 (Foxn1) and autoimmune regulator (AIRE) in the thymus tissue of mice from the HTN group were significantly lower than those from the control group at 4 and 8 weeks (P<0.05). Foxn1 and AIRE expression was also reduced in the sham surgery group at 4 weeks after surgery, but had recovered 4 weeks later. Similar results were observed for the expression of signal-joint T cell receptor excision circles and the percentages of T cell subsets. The present study indicates that impaired thymus function is associated with hypertension in mice, which suggests that thymus function may be a novel target for the treatment of patients with hypertension.

Non-genotoxic conditioning for hematopoietic stem cell transplantation using a hematopoietic-cell-specific internalizing immunotoxin

Hematopoietic stem cell transplantation (HSCT) offers curative therapy for patients with hemoglobinopathies, congenital immunodeficiencies, and other conditions, possibly including AIDS. Autologous HSCT using genetically corrected cells would avoid the risk of graft-versus-host disease (GVHD), but the genotoxicity of conditioning remains a substantial barrier to the development of this approach. Here we report an internalizing immunotoxin targeting the hematopoietic-cell-restricted CD45 receptor that effectively conditions immunocompetent mice. A single dose of the immunotoxin, CD45-saporin (SAP), enabled efficient (>90%) engraftment of donor cells and full correction of a sickle-cell anemia model. In contrast to irradiation, CD45-SAP completely avoided neutropenia and anemia, spared bone marrow and thymic niches, enabling rapid recovery of T and B cells, preserved anti-fungal immunity, and had minimal overall toxicity. This non-genotoxic conditioning method may provide an attractive alternative to current conditioning regimens for HSCT in the treatment of non-malignant blood diseases.

Population Distributions of Thymic Function in Adults: Variation by Sociodemographic Characteristics and Health Status

The thymus is critical for mounting an effective immune response and maintaining health. However, epidemiologic studies characterizing thymic function in the population setting are lacking. Using data from 263 adults in the Detroit Neighborhood Health Study, we examined thymic function as measured by the number of signal joint T-cell receptor excision circles (sjTREC) and assessed associations with established indicators of physiological health. Overall, increasing age and male gender were significantly associated with reduced thymic function. Adjusting for covariates, individuals with elevated levels of the pro-inflammatory biomarkers C-reactive protein (β: -0.50 [95% CI: -0.82, -0.18] for moderate elevation, β: -0.29 [95% CI: -0.59, 0.00] for high elevation) and interleukin-6 (β: -0.60 [95% CI: -0.92, -0.28] for moderate elevation, β: -0.43 [95% CI: -0.77, -0.08] for severe elevation) also had lower thymic function. Compared to individuals with a BMI < 25, individuals who were overweight (β: 0.36 [95% CI: 0.07, 0.64]) or obese (β: 0.27 [95% CI: -0.03, 0.56]) had higher thymic function. Differences by self-rated health were not statistically significant. Our findings underscore demographic- and health-related gradients in thymic function among adult residents of Detroit, suggesting thymic function may be an important biomarker of health status in adults at the population level.

CD4(+) CD44(v.low) cells are unique peripheral precursors that are distinct from recent thymic emigrants and stem cell-like memory cells

CD4(+) CD44(v.low) cells are peripheral precursor T cells that inhibit lymphopenia by generating a large CD4(+) T cell pool containing balanced numbers of naïve, memory, and regulatory Foxp3(+) cells with a diverse TCR repertoire. Recent thymic emigrants (RTE) and stem cell-like memory T cells (T(SCM)) can also replenish a T cell pool. In this study we formally test whether CD44(v.low) cells are the same population as RTE and T(SCM). Our data show that, in contrast to RTE, CD44(v.low) cells express high levels of CD45RB and low levels of CD24. Moreover, CD44(v.low) cells isolated from mice devoid of RTE retain their capacity to repopulate lymphopenic mice with naïve and memory cells and Foxp3(+) Tregs. In addition, CD44(v.low) cells do not express IL-2Rβ, Sca-1, and CXCR3, the phenotypic hallmarks of T(SCM). Overall, these data demonstrate that CD44(v.low) cells are neither RTE nor T(SCM).

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

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.