Assessment of atherosclerosis in chronic granulomatous disease.

BACKGROUND: Patients with chronic granulomatous disease (CGD) experience immunodeficiency because of defects in the phagocyte NADPH oxidase and the concomitant reduction in reactive oxygen intermediates. This may result in a reduction in atherosclerotic injury. METHODS AND RESULTS: We prospectively assessed the prevalence of cardiovascular risk factors, biomarkers of inflammation and neutrophil activation, and the presence of magnetic resonance imaging and computed tomography quantified subclinical atherosclerosis in the carotid and coronary arteries of 41 patients with CGD and 25 healthy controls in the same age range. Univariable and multivariable associations among risk factors, inflammatory markers, and atherosclerosis burden were assessed. Patients with CGD had significant elevations in traditional risk factors and inflammatory markers compared with control subjects, including hypertension, high-sensitivity C-reactive protein, oxidized low-density lipoprotein, and low high-density lipoprotein. Despite this, patients with CGD had a 22% lower internal carotid artery wall volume compared with control subjects (361.3±76.4 mm(3) versus 463.5±104.7 mm(3); P<0.001). This difference was comparable in p47(phox)- and gp91(phox)-deficient subtypes of CGD and independent of risk factors in multivariate regression analysis. In contrast, the prevalence of coronary arterial calcification was similar between patients with CGD and control subjects (14.6%, CGD; 6.3%, controls; P=0.39). CONCLUSIONS: The observation by magnetic resonance imaging and computerized tomography of reduced carotid but not coronary artery atherosclerosis in patients with CGD despite the high prevalence of traditional risk factors raises questions about the role of NADPH oxidase in the pathogenesis of clinically significant atherosclerosis. Additional high-resolution studies in multiple vascular beds are required to address the therapeutic potential of NADPH oxidase inhibition in cardiovascular diseases. CLINICAL TRIAL REGISTRATION URL: http://www.clinicaltrials.gov. Unique identifier: NCT01063309.

Residual NADPH oxidase and survival in chronic granulomatous disease.

BACKGROUND: Failure to generate phagocyte-derived superoxide and related reactive oxygen intermediates (ROIs) is the major defect in chronic granulomatous disease, causing recurrent infections and granulomatous complications. Chronic granulomatous disease is caused by missense, nonsense, frameshift, splice, or deletion mutations in the genes for p22(phox), p40(phox), p47(phox), p67(phox) (autosomal chronic granulomatous disease), or gp91(phox) (X-linked chronic granulomatous disease), which result in variable production of neutrophil-derived ROIs. We hypothesized that residual ROI production might be linked to survival in patients with chronic granulomatous disease. METHODS: We assessed the risks of illness and death among 287 patients with chronic granulomatous disease from 244 kindreds. Residual ROI production was measured with the use of superoxide-dependent ferricytochrome c reduction and flow cytometry with dihydrorhodamine oxidation assays. Expression of NADPH oxidase component protein was detected by means of immunoblotting, and the affected genes were sequenced to identify causal mutations. RESULTS: Survival of patients with chronic granulomatous disease was strongly associated with residual ROI production as a continuous variable, independently of the specific gene affected. Patients with mutations in p47(phox) and most missense mutations in gp91(phox) (with the exception of missense mutations in the nucleotide-binding and heme-binding domains) had more residual ROI production than patients with nonsense, frameshift, splice, or deletion mutations in gp91(phox). After adolescence, mortality curves diverged according to the extent of residual ROI production. CONCLUSIONS: Patients with chronic granulomatous disease and modest residual production of ROI have significantly less severe illness and a greater likelihood of long-term survival than patients with little residual ROI production. The production of residual ROI is predicted by the specific NADPH oxidase mutation, regardless of the specific gene affected, and it is a predictor of survival in patients with chronic granulomatous disease. (Funded by the National Institutes of Health.).

Study design and baseline profile for adults with type 2 diabetes in the once-weekly subcutaneous SEmaglutide randomized PRAgmatic (SEPRA) trial.

INTRODUCTION: Once-weekly subcutaneous semaglutide, a glucagon-like peptide-1 analog, is approved in the USA as an adjunct to diet and exercise for adults with inadequately controlled type 2 diabetes (T2D) to improve glycemic control and reduce the risk of major adverse cardiovascular events in people with T2D and established cardiovascular disease. The Semaglutide Unabated Sustainability in Treatment of Type 2 Diabetes (SUSTAIN) phase III clinical trial program demonstrated the efficacy and safety of once-weekly subcutaneous semaglutide; however, determining its effectiveness in a real-world setting could support decision-making by clinicians, payers and policy makers in routine clinical practice. RESEARCH DESIGN AND METHODS: SEmaglutide PRAgmatic (SEPRA) is an ongoing open-label, randomized, pragmatic clinical trial designed to compare the effects of once-weekly subcutaneous semaglutide versus standard of care in US health-insured adults with T2D and physician-determined inadequate glycemic control. The primary end point is the proportion of participants achieving glycated hemoglobin (HbA1c) <7.0% at year 1; other key outcomes include glycemic control, weight loss, healthcare utilization, and patient-reported outcomes. Individual-level data will be collected from routine clinical practice and health insurance claims. The last patient last visit is expected by June 2023. RESULTS: Between July 2018 and March 2021, 1278 participants were enrolled from 138 study sites across the USA. At baseline, 54% were male with mean±SD age 57.4±11.1 years and body mass index 35.7±8.0 kg/m2. Mean diabetes duration was 7.4±6.0 years and mean HbA1c was 8.5±1.6%. At baseline, concomitant antidiabetes medications included metformin, sulfonylureas, sodium-glucose co-transporter-2 inhibitors, and dipeptidyl peptidase-4 inhibitors. The majority of participants had hypertension and dyslipidemia. The trial design was self-assessed using the PRagmatic Explanatory Continuum Indicator Summary-2 tool by the study steering group and was scored 4-5 in all domains suggesting a highly pragmatic study. CONCLUSIONS: SEPRA, a highly pragmatic ongoing study, will provide data on the effects of once-weekly subcutaneous semaglutide in a real-world setting when used during routine management of T2D. TRIAL REGISTRATION NUMBER: NCT03596450.

Sustained Remission and Outcomes with Abatacept plus Methotrexate Following Stepwise Dose De-escalation in Patients with Early Rheumatoid Arthritis.

INTRODUCTION: One target of rheumatoid arthritis (RA) treatment is to achieve early sustained remission; over the long term, patients in sustained remission have less structural joint damage and physical disability. We evaluated Simplified Disease Activity Index (SDAI) remission with abatacept + methotrexate versus abatacept placebo + methotrexate and impact of de-escalation (DE) in anti-citrullinated protein antibody (ACPA)-positive patients with early RA. METHODS: The phase IIIb, randomized, AVERT-2 two-stage study (NCT02504268) evaluated weekly abatacept + methotrexate versus abatacept placebo + methotrexate. PRIMARY ENDPOINT: SDAI remission (≤ 3.3) at week 24. Pre-planned exploratory endpoint: maintenance of remission in patients with sustained remission (weeks 40 and 52) who, from week 56 for 48 weeks (DE period), (1) continued combination abatacept + methotrexate, (2) tapered abatacept to every other week (EOW) + methotrexate for 24 weeks with subsequent abatacept withdrawal (abatacept placebo + methotrexate), or (3) withdrew methotrexate (abatacept monotherapy). RESULTS: Primary study endpoint was not met: 21.3% (48/225) of patients in the combination and 16.0% (24/150) in the abatacept placebo + methotrexate arm achieved SDAI remission at week 24 (p = 0.2359). There were numerical differences favoring combination therapy in clinical assessments, patient-reported outcomes (PROs) and week 52 radiographic non-progression. After week 56, 147 patients in sustained remission with abatacept + methotrexate were randomized (combination, n = 50; DE/withdrawal, n = 50; abatacept monotherapy, n = 47) and entered DE. At DE week 48, SDAI remission (74%) and PRO improvements were mostly maintained with continued combination therapy; lower remission rates were observed with abatacept placebo + methotrexate (48.0%) and with abatacept monotherapy (57.4%). Before withdrawal, de-escalating to abatacept EOW + methotrexate preserved remission. CONCLUSIONS: The stringent primary endpoint was not met. However, in patients achieving sustained SDAI remission, numerically more maintained remission with continued abatacept + methotrexate versus abatacept monotherapy or withdrawal. TRIAL REGISTRATION: ClinicalTrials.gov identifier, NCT02504268. Video abstract (MP4 62241 KB).

Patients with rheumatoid arthritis (RA) experience inflamed and damaged joints. RA is an autoimmune disease in which proteins called autoantibodies, particularly anti-citrullinated protein autoantibodies, target the patient's own joint tissue and organs by mistake, leading to symptomatic inflammation. Successful treatment can decrease the disease's activity to a state known as remission. Patients in remission may experience little or no symptoms and it may be possible for some to then be able to decrease their treatment. Here, we report the results of a large, international study that looked at two treatments, abatacept and methotrexate, in patients with RA and anti-citrullinated protein autoantibodies. The study had two parts. Firstly, to see how many patients had success (remission) with weekly abatacept and/or methotrexate treatment, and secondly, to see if remission was maintained when treatment was either continued or decreased and stopped. The study showed that the number of patients in remission 6 months after treatment started was not greatly different between patients treated with both abatacept and methotrexate and those treated with just methotrexate. Those taking abatacept and methotrexate together had better remission rates 1 year later. More patients also stayed in remission when they continued to receive both abatacept and methotrexate compared with those who were just treated with abatacept or when their abatacept treatment was decreased and stopped. More patients stayed in remission when abatacept was decreased than when it was stopped. The results from this study may help determine possible future treatment reduction and/or withdrawal plans for some patients with RA.

Safety of Abatacept Versus Placebo in Rheumatoid Arthritis: Integrated Data Analysis of Nine Clinical Trials.

OBJECTIVE: To assess the safety of abatacept treatment in rheumatoid arthritis (RA) using integrated data from multiple clinical trials. METHODS: Data from nine double-blind, placebo-controlled studies of abatacept treatment (seven intravenous, two subcutaneous) in patients with RA were pooled, focusing on safety events in the double-blind treatment period of each study. Incidence rates (IRs) of adverse events (AEs) per 100 patient-years of exposure were calculated for abatacept- and placebo-treated patients. AEs in abatacept-treated patients were combined regardless of dose and formulation. RESULTS: In total, 2653 patients received abatacept and 1485 received placebo, with 2357 and 1254 patient-years of exposure, respectively. The mean (SD) durations of exposure in the abatacept and placebo groups were 10.8 (3.3) and 10.3 (3.5) months, respectively. The IRs (95% confidence interval [CI]) for serious AEs were 14.8 (13.3, 16.5) and 14.6 (12.5, 17.0) in the abatacept and placebo groups, respectively. Death occurred in 12 (0.5%) and 12 (0.8%) patients in the abatacept and placebo groups, respectively, and was most commonly caused by cardiac disorders. Malignancies were observed in 31 patients (1.2%) treated with abatacept (IR: 1.32 [95% CI: 0.90, 1.87]) versus 14 (0.9%; IR: 1.12 [0.61, 1.88]) who received placebo. Solid organ tumor was the most frequent malignancy reported in both groups (abatacept: 1.0%; IR: 1.11 [95% CI: 0.72, 1.62]; placebo: 0.8%; 0.96 [0.50, 1.67]). CONCLUSION: In this integrated analysis, the IRs of safety events in the abatacept and placebo groups were similar with no new safety concerns identified.

Intrarectal amifostine during external beam radiation therapy for prostate cancer produces significant improvements in Quality of Life measured by EPIC score.

PURPOSE: To test whether intrarectal amifostine limits symptoms of radiation proctitis, measured by using the Radiation Therapy Oncology Group (RTOG) gastrointestinal (GI) toxicity score and the Expanded Prostate Cancer Index Composite (EPIC) score. METHODS AND MATERIALS: Patients with localized prostate cancer received amifostine as a rectal suspension 30-45 minutes before daily three-dimensional conformal radiation therapy. The first 18 patients received 1 g of amifostine, and the next 12 patients received 2 g. Toxicity was assessed at baseline, during treatment, and at follow-up visits by using RTOG grading and the EPIC Quality of Life (QoL) 50-item questionnaire. The Bowel Function subset of the bowel domain (EPIC-BF), which targets symptom severity, and the Bowel Bother subset of the bowel domain (EPIC-BB), which assesses QoL, were evaluated and compared with the RTOG GI toxicity score. RESULTS: Median follow-up was 30 months (range, 18-36 months). Overall, EPIC-BF and EPIC-BB scores both tracked closely with the RTOG GI toxicity score. Seven weeks after the start of radiation therapy, the incidence of RTOG Grade 2 toxicity was 33% in the 1-g group (6/18 patients) compared with 0% (0/12 patients) in the 2-g group and tended toward statistical significance (p = 0.06). A significant difference between amifostine groups was observed using the EPIC-BF score at 7 weeks (p = 0.04). A difference in EPIC-BB scores between dose groups was evident at 7 weeks (p = 0.07) and was significant at 12 months (p = 0.04). CONCLUSIONS: Higher doses of amifostine produced significant improvements in acute and late bowel QoL (up to 1 year after therapy), measured using the EPIC score.

Pretreatment predictors of death from other causes in men with prostate cancer.

PURPOSE: Most men diagnosed with prostate cancer will die of other causes and pretreatment patient characteristics may identify those who are likely to die of other causes. Accurate stratification of patients by risk of other cause mortality may reduce needless treatment preventing morbidity and expense. MATERIALS AND METHODS: Using the CaPSURE database a cohort of men was identified with clinically localized prostate cancer who had definitive treatment with radical prostatectomy or radiation therapy between 1995 and 2004. Pretreatment patient characteristics were evaluated to determine if early other cause mortality could be predicted. RESULTS: Of 13,124 subjects enrolled in CaPSURE 5,070 had clinical T1c-T3a prostatic adenocarcinoma treated with radical prostatectomy (77%) or radiation therapy (23%) and posttreatment followup data. Median followup was 3.3 years. The cohort was divided into 3 groups. The prostate cancer specific mortality group included 55 men (1%) who died of prostate cancer. The 296 men (6%) who died of causes other than prostate cancer comprised the other cause mortality group. A third group contained the 4,719 (93%) men surviving at the end of the observation period. Factors that exclusively predicted death from nonprostate cancer causes included age at diagnosis, having a high school education or less, high clinical risk, smoking at time of diagnosis, concurrent nonprostate malignancy and worse scores on the Short Form-36 Health Survey physical function scale. CONCLUSIONS: Several pretreatment patient characteristics may identify patients at high risk of nonprostate cancer mortality. Future studies should consider stratifying patients by or at least reporting these variables.

Assessment of tissue redox status using metabolic responsive contrast agents and magnetic resonance imaging.

Regulation of tissue redox status is important to maintain normal physiological conditions in the living body. Disruption of redox homoeostasis may lead to oxidative stress and can induce many pathological conditions such as cancer, neurological disorders and ageing. Therefore, imaging of tissue redox status could have clinical applications. Redox imaging employing magnetic resonance imaging (MRI) with nitroxides as cell-permeable redox-sensitive contrast agents has been used for non-invasive monitoring of tissue redox status in animal models. The redox imaging applications of nitroxide electron paramagnetic resonance imaging (EPRI) and MRI are reviewed here, with a focus on application of tumour redox status monitoring. While particular emphasis has been placed on differences in the redox status in tumours compared to selected normal tissues, the technique possesses the potential to have broad applications to the study of other disease states, inflammatory processes and other circumstances where oxidative stress is implicated.

The chemistry and biology of nitroxide compounds.

Cyclic nitroxides are a diverse group range of stable free radicals that have unique antioxidant properties. Because of their ability to interact with free radicals, they have been used for many years as biophysical tools. During the past 15-20 years, however, many interesting biochemical interactions have been discovered and harnessed for therapeutic applications. Biologically relevant effects of nitroxides have been described, including their ability to degrade superoxide and peroxide, inhibit Fenton reactions, and undergo radical-radical recombination. Cellular studies defined the activity of nitroxides in vitro. By modifying oxidative stress and altering the redox status of tissues, nitroxides have been found to interact with and alter many metabolic processes. These interactions can be exploited for therapeutic and research use, including protection against ionizing radiation, as probes in functional magnetic resonance imaging, cancer prevention and treatment, control of hypertension and weight, and protection from damage resulting from ischemia/reperfusion injury. Although much remains to be done, many applications have been well studied and some are currently being tested in clinical trials. The therapeutic and research uses of nitroxide compounds are reviewed here with a focus on the progress from initial development to modern trials.

Therapeutic and clinical applications of nitroxide compounds.

Nitroxide compounds have been used for many years as biophysical tools, but only during the past 15-20 years have the many interesting biochemical interactions been discovered and harnessed for therapeutic applications. By modifying oxidative stress and altering the redox status of tissues, nitroxides have the ability to interact with and alter many metabolic processes. This interaction can be exploited for therapeutic and research use, including protection against ionizing radiation, as probes in functional magnetic resonance imaging, cancer prevention and treatment, control of hypertension and weight, and protection from damage resulting from ischemia/reperfusion injury. Although much remains to be done, many applications have been well studied, and some are presently being tested in clinical trials. The therapeutic and research uses of nitroxides are reviewed here, with a focus on the progress from initial development to modern, state-of-the art trials.

MicroRNA expression altered by diet: can food be medicinal?

As the link between metabolism and major disease processes becomes more well-defined, the identification of key molecular targets is leading to new therapeutic strategies. As a result, small non-coding RNA molecules that regulate gene expression via epigenetic alterations, microRNAs have been identified as regulators of these metabolic processes. In the last decade, dietary interventions have been used to change metabolism and to potentially alter disease progression and clinical outcomes. These interventions have been linked, at a molecular level, to microRNAs. This review will summarize the role of various dietary strategies on the expression of several microRNA families.

Cellular stress induced alterations in microRNA let-7a and let-7b expression are dependent on p53.

Genotoxic stressors, such as radiation, induce cellular damage that activates pre-programmed repair pathways, some of which involve microRNAs (miRNA) that alter gene expression. The let-7 family of miRNA regulates multiple cellular processes including cell division and DNA repair pathways. However, the role and mechanism underlying regulation of let-7 genes in response to stress have yet to be elucidated. In this study we demonstrate that let-7a and let-7b expression decreases significantly following exposure to agents that induce stress including ionizing radiation. This decrease in expression is dependent on p53 and ATM in vitro and is not observed in a p53(-/-) colon cancer cell line (HCT116) or ATM(-/-) human fibroblasts. Chromatin Immunoprecipitation (ChIP) analysis showed p53 binding to a region upstream of the let-7 gene following radiation exposure. Luciferase transient transfections demonstrated that this p53 binding site is necessary for radiation-induced decreases in let-7 expression. A radiation-induced decrease in let-7a and let-7b expression is also observed in radiation-sensitive tissues in vivo and correlates with altered expression of proteins in p53-regulated pro-apoptotic signaling pathways. In contrast, this decreased expression is not observed in p53 knock-out mice suggesting that p53 directly repress let-7 expression. Exogenous expression of let-7a and let-7b increased radiation-induced cytotoxicity in HCT116 p53(+/+) cells but not HCT116 p53(-/-) cells. These results are the first demonstration of a mechanistic connection between the radiation-induced stress response and the regulation of miRNA and radiation-induced cytotoxicity and suggest that this process may be a molecular target for anticancer agents.

Loratadine dysregulates cell cycle progression and enhances the effect of radiation in human tumor cell lines.

BACKGROUND: The histamine receptor-1 (H1)-antagonist, loratadine has been shown to inhibit growth of human colon cancer xenografts in part due to cell cycle arrest in G2/M. Since this is a radiation sensitive phase of the cell cycle, we sought to determine if loratadine modifies radiosensitivity in several human tumor cell lines with emphasis on human colon carcinoma (HT29). METHODS: Cells were treated with several doses of loratadine at several time points before and after exposure to radiation. Radiation dose modifying factors (DMF) were determined using full radiation dose response survival curves. Cell cycle phase was determined by flow cytometry and the expression of the cell cycle-associated proteins Chk1, pChk1(ser345), and Cyclin B was analyzed by western blot. RESULTS: Loratadine pre-treatment of exponentially growing cells (75 microM, 24 hours) increased radiation-induced cytotoxicity yielding a radiation DMF of 1.95. However, treatment of plateau phase cells also yielded a DMF of 1.3 suggesting that mechanisms other than cell cycle arrest also contribute to loratadine-mediated radiation modification. Like irradiation, loratadine initially induced G2/M arrest and activation of the cell-cycle associated protein Chk1 to pChk1(ser345), however a subsequent decrease in expression of total Chk1 and Cyclin B correlated with abrogation of the G2/M checkpoint. Analysis of DNA repair enzyme expression and DNA fragmentation revealed a distinct pattern of DNA damage in loratadine-treated cells in addition to enhanced radiation-induced damage. Taken together, these data suggest that the observed effects of loratadine are multifactorial in that loratadine 1) directly damages DNA, 2) activates Chk1 thereby promoting G2/M arrest making cells more susceptible to radiation-induced DNA damage and, 3) downregulates total Chk1 and Cyclin B abrogating the radiation-induced G2/M checkpoint and allowing cells to re-enter the cell cycle despite the persistence of damaged DNA. CONCLUSIONS: Given this unique possible mechanism of action, loratadine has potential as a chemotherapeutic agent and as a modifier of radiation responsiveness in the treatment of cancer and, as such, may warrant further clinical evaluation.

Ionizing radiation-induced oxidative stress alters miRNA expression.

BACKGROUND: MicroRNAs (miRNAs) are small, highly conserved, non-coding RNA that alter protein expression and regulate multiple intracellular processes, including those involved in the response to cellular stress. Alterations in miRNA expression may occur following exposure to several stress-inducing anticancer agents including ionizing radiation, etoposide, and hydrogen peroxide (H(2)O(2)). METHODOLOGY/PRINCIPAL FINDINGS: Normal human fibroblasts were exposed to radiation, H(2)O(2), or etoposide at doses determined by clonogenic cell survival curves. Total RNA was extracted and miRNA expression was determined by microarray. Time course and radiation dose responses were determined using RT-PCR for individual miRNA species. Changes in miRNA expression were observed for 17 miRNA species following exposure to radiation, 23 after H(2)O(2) treatment, and 45 after etoposide treatment. Substantial overlap between the miRNA expression changes between agents was observed suggesting a signature miRNA response to cell stress. Changes in the expression of selected miRNA species varied in response to radiation dose and time. Finally, production of reactive oxygen species (ROS) increased with increasing doses of radiation and pre-treatment with the thiol antioxidant cysteine decreased both ROS production and the miRNA response to radiation. CONCLUSIONS: These results demonstrate a common miRNA expression signature in response to exogenous genotoxic agents including radiation, H(2)O(2), and etoposide. Additionally, pre-treatment with cysteine prevented radiation-induced alterations in miRNA expression which suggests that miRNAs are responsive to oxidative stress. Taken together, these results imply that miRNAs play a role in cellular defense against exogenous stress and are involved in the generalized cellular response to genotoxic oxidative stress.

Oral pirfenidone in patients with chronic fibrosis resulting from radiotherapy: a pilot study.

BACKGROUND: Fibrosis is a common side effect after treatment with ionizing radiation. Several methods to ameliorate debilitating fibrosis have been employed but without consistent results. The goal of this pilot study is to determine if Pirfenidone, a novel regulator of cytokine gene expression, has the potential to ameliorate established radiation-induced fibrosis. METHODS: Open label, prospective pilot study of 800 mg three times/day, orally administered Pirfenidone was administered to enrolled patients who were had completed radiation therapy and who had established radiation-induced fibrosis. Range of motion (ROM) was assessed using standard measures, and subjective measures of pain, fatigue, disability and global health were measured every three months. RESULTS: Seven patients were enrolled of whom 3 had ROM assessments of 1 site and 2 had ROM assessments of 2 sites. Of these assessments, 6 revealed increased ROM during drug intervention while 1 revealed a decreased ROM. There was an overall improvement in the mental composite score of the SF36 while physical composite score was decreased and the vitality score was unchanged. Two patients were removed from the study because of syncopal episodes. CONCLUSION: Several patients experienced improved function of at least 25% and reported subjective improvement. Pirfenidone may benefit patients with radiation-induced fibrosis and is worthy of a larger well controlled trial.

Effects of gamma radiation on FcepsilonRI and TLR-mediated mast cell activation.

Ionizing gamma radiation has several therapeutic indications including bone marrow transplantation and tumor ablation. Among immune cells, susceptibility of lymphocytes to gamma radiation is well known. However, there is little information on the effects of gamma radiation on mast cells, which are important in both innate and acquired immunity. Previous studies have suggested that mast cells may release histamine in response to high doses of gamma radiation, whereas other reports suggest that mast cells are relatively radioresistant. No strong link has been established between gamma radiation and its effect on mast cell survival and activation. We examined both human and murine mast cell survival and activation, including mechanisms related to innate and acquired immune responses following gamma radiation. Data revealed that human and murine mast cells were resistant to gamma radiation-induced cytotoxicity and, importantly, that irradiation did not directly induce beta-hexosaminidase release. Instead, a transient attenuation of IgE-mediated beta-hexosaminidase release and cytokine production was observed which appeared to be the result of reactive oxygen species formation after irradiation. Mast cells retained the ability to phagocytose Escherichia coli particles and respond to TLR ligands as measured by cytokine production after irradiation. In vivo, there was no decrease in mast cell numbers in skin of irradiated mice. Additionally, mast cells retained the ability to respond to Ag in vivo as measured by passive cutaneous anaphylaxis in mice after irradiation. Mast cells are thus resistant to the cytotoxic effects and alterations in function after irradiation and, despite a transient inhibition, ultimately respond to innate and acquired immune activation signals.