Effects of radiation and latent virus on immune responses in a space flight model

Background: The immunosuppressive effects of space flight radiation and reactivation of latent virus infections in human beings are largely unknown. Objective: To develop a murine model that can predict the adverse effects of space flight radiation and reactivation of latent virus infection for human beings. Methods: In experiment I, some BALB/c mice received whole-body gamma-irradiation (3 Gy) on day 0 and murine polyoma virus (PyV) on day 1. In experiment II, mice received irradiation (3 Gy) or none on days 0 and/or 49, and PyV or none on day 1: A1, 3 Gy/PyV/3 Gy; A2, 3 Gy/PyV/0 Gy; B1, 0 Gy/PyV/3 Gy; B2, 0 Gy/PyV/0 Gy; C, 3 Gy/0 PyV/0 Gy; and D, 0 Gy/0 PyV/0 Gy. Results: In experiment 1, PyV was detected by PCR more frequently in several host organs tested and for a longer period of time in irradiated than in control animals. In experiment II, PyV replication in the spleen was detected in A1 > B1 mice on days 10 and 20; both groups cleared PyV by day 49. After irradiation on day 49, reactivated PyV was detected in more B1 than A I mice. A I mice had lower spleen weights and cell counts than other groups at all time points. From 0 to 49 days, irradiation suppressed spleen cell proliferation to concanavalin A in all irradiated groups except in BI when the virus was cleared at day 20. PyV enhanced IFN-gamma production in all groups: B1 > A1 > C, D (0-49 days; all differences, P <.05). Conclusion: This small animal model or space flight suggests that the combined effects of radiation and virus replication will significantly affect T-Iymphocyte-mediated immunity that may lead to chronic viral infection and malignancy.