Low dose radiation response in the lungs and spleen

Abstract

Patients in the intensive and critical care unit frequently undergo diagnostic radiology procedures such as computed tomography (CT) and X-ray imaging. As these patients often require respiratory assistance and are vulnerable to infection, it is important to understand the potential acute effects of these procedures on the lungs and immune system. The aim of this study was to determine the acute effects of a single clinically relevant low-dose X-ray exposure in order to establish baseline responses in markers of lung injury and immune function in a rodent model. Male Sprague-Dawley rats (200-250 g) were irradiated with 0, 2, 20 or 200 mGy whole-body X-rays in an XRAD 320 irradiator. Markers of lung injury and immune activation in the lungs and spleen were evaluated 0.5, 4, and 24 h post-irradiation to examine the acute stages of the physiological and immunological response. Intratrachaeal lipopolysaccharide (LPS) exposure was used as a positive control model of acute lung injury. Lung injury endpoints included respiratory mechanics, pulmonary oedema, arterial blood oxygenation, histological analysis, and cellular and proteinaceous infiltrate via bronchoalveolar lavage. Immunological measures in the spleen focused on splenocyte proliferation, using the MTS assay and differential cell counts before and after stimulation with LPS or concanavalin A (Con A), as compared to unstimulated cultures. Splenocyte proliferation in response to Con A, but not LPS, was significantly decreased after 200 mGy in vivo X-irradiation (repeated measures two-way ANOVA with LSD post-hoc, p=0.024). There was a non-significant trend towards increased lung tissue resistance after 200 mGy, with no significant effect on pulmonary oedema, cellular or proteinaceous infiltrate, nor other aspects of respiratory mechanics (two-way ANOVA with LSD post-hoc, p>0.05). A clear understanding of these immunological and physiological effects informs the responsible use of medical diagnostic procedures in modern medicine. Establishment of this model for the elucidation of acute immune effects of low-dose radiation will facilitate future work evaluating these parameters in disease models, mimicking patients in intensive care.