Immune status of the nuclear plant workers in the long-term period after occupational exposure

Long-term clinical and epidemiological studies carried out in Russia have revealed a reliable linkage of onco-pathology with radiation exposure to the personnel of 'Mayak' Production Association (PA). At present most of the 'Mayak' veterans exposed to radiation during the first years of professional activity and accidents have reached the age of manifestation deleterious effects f chronic radiation exposure, including malignant neoplasms. According to the data published in a number of papers, immune and natural leukocyte resistance abnormalities have been observing for a long time after occupational exposure in doses significantly exceeding the limiting dose (dose limit DL). Long term studies were performed using large experimental material, we demonstrated stable immune abnormalities in animals of different species in the late period after exposure to high doses of chronic radiation. Incomplete recovery was revealed predominantly in T-system and also in the compartment of poly-potent and committed lymphatic precursors. The observed abnormalities, caused by residual radiation damage of blood-forming and immune systems, can be realized both directly and indirectly via formation of deterministic and/or somato-stochastic radiation effects. In this connection, studying of dependence of the frequency and character of immune abnormalities on the exposure level will enable to provide prediction of long-term consequences of chronic radiation, develop a survey program to form groups of risk of immunological deficiency, and design a scheme of timely prophylaxis and treatment techniques. The aim of present study was assessment of the immune status in the nuclear enterprise workers in the long-term period after occupational exposure and determination of dependence of the frequency of immune abnormalities on the accumulated radiation dose. The sample groups studied were form mainly of currently retired 'Mayak' workers, whose occupational activity had begun 45-50 years ago, during the period of the most unfavorable situation at the enterprise (341 individuals). Control group was also formed by PA 'Mayak' (73 individuals) professionals, mean accumulated external gamma-exposure dose for the whole period of occupation in individuals from this group did not exceed DL (9.5 ± 0.4 cGy). The status of humoral, cellular immunity, non-specific resistance factors and content of pro-inflammatory interleukins Il-1β and TNF α in 'Mayak' workers, subjected mainly to combined exposure due to external γ-exposure doses (accumulated doses from 0.5 to 7.90 Gy) and internal α-exposure doses due to incorporated 239Pu (plutonium body burden from 0.19 to 4.7 kBq). A decrease of cellular (lower, then comparison group on 15-25%), some of humoral immunity parameters at total doses over 1 Gy, content of NK (on 25-35%) and phagocytes (on 14-33%) at doses over 1 and 2 Gy, was identified. The index of cytotoxic function of leukocytes in t he individuals with the mean doses over 4 Gy also was lower on 17%, than in control group. During the study, we also revealed an increase in the level of cytokines in patients, whose doses exceeded DL. Statistically significant direct dependence of infectious syndrome incidence on accumulated exposure dose was shown in morbidity studies. (authors)