The immune system in irradiated animals at a dose of 6 Gy
Our study showed that exposure of experimental animals to a high dose of radiation in a remote period acted as an immunosuppressive agent, revealing a significant sensitivity of leukocytes and T-lymphocytes and their subpopulations. Hence, we observed the occurrence of leukopenia in exposed animals; the number of leukocytes was reduced by 18.72 % (p < 0.05) (Table 1 ).
At the same time, both the percentage and the absolute number of lymphocytes were shown to be increased by 8.58 % (p < 0.05) and 5.74 % (p < 0.05), respectively. Regarding T-lymphocytes, we identified the following changes: the total number of lymphocytes was reduced by almost 45,03 % (p < 0,001), and the relative number by 35,12 % (p < 0,05), leading to a significant reduction of cells with CD4+ helper activity: the total number was reduced by 26,32 % (p < 0,05), and the relative number by 30,27 % (p < 0,05). Thus, the immunoregulatory index (IRI = CD4+/CD8+) in animals exposed to radiation was reduced in comparison with the intact group. In the case of T-suppressors, an inhibition of their activity was observed, also exhibiting a decrease in the total and relative number by 22.22 % (p < 0.05)and 36.86 % (p < 0.01), respectively. It is known that the activity of the CD3+ lymphocyte lymphokine-producing cells reflects the functional activity of the T-system of immunity. Our study revealed a decrease in the production capacity of CD3+ lymphocytes in irradiated animals, as well as a 32.56 % increase in the LMIR migration index in the PHA-treated compared with the control group (p < 0.05). We found that the ability of cells to produce cytokines suppressing the migration of leukocytes was expressed in the control group. Whereas, in animals under the influence of gamma radiation, the production of cytokines was reduced, thus indicating the immunosuppressive action of radiation, which led to the suppression of the synthesis of cytokines, as the migration index was higher than that in intact animals. According to several researchers [28,29], ionizing radiation could cause a decrease in DNA synthesis, and the number of cells transformed into blasts under the influence of PHA, reducing the production of the factor inhibiting the migration of macrophages (MIF) and the associated cytotoxic effect.
Against the background of the explicit suppression of cell immunity, we obtained the result of the immunoregulatory index (CD4+/CD8+), exhibiting a shift to the left towards a decrease. The decrease in IRI is considered to be typical in immunodeficiency states, and cancers. Thus, the pathognomonic laboratory symptom of immune deficiency was shown to gradually include incomplete numbers of CD4+ and a decrease of IRI. The decrease observed in IRI in our example was assumed to be due to a sharp decrease in the number of T-cells with helper activity compared with those of T-cells with suppressor activity. As is known, CD4+ cells stimulate the CD19+ lymphocyte population for production of antibodies. Insufficient helper function of T-lymphocytes might lead to a decrease in the sensitivity of the body to antigenic stimulation, contributing to the development of severe infectious complications, and pathological conditions of radiation genesis.
Taking into account the complexity of the character of changes in the of humoral immunity with the radiation lesion of the organism, we aimed to study the long term reaction of humoral immunity in interrelation with the nonspecific phagocytic link of immunity at the same dose of 6 Gy gamma-irradiation. To determine the state of humoral and nonspecific phagocytic links of immunity in the case of gamma-irradiation, we studied the number of CD19+ lymphocytes, the concentration of CIC, serum immunoglobulins, phagocytic activity, phagocytic number, and also performed a NTT-test.
The suppressed levels of CD4+ cells, as well as the persistent level of CD19+ cells indicated the implementation of the immune response, which, thus, activated the B-cells; proof of this was a reliable increase in the absolute and relative number of CD19+ lymphocytes in the blood by 37.5 % and 41.99 %, respectively compared with control (p < 0.05). B-lymphocytes, in turn, are known to switch from IgM synthesis to IgG and IgA synthesis as they mature, but in this case we observed a suppression in the levels of IgG and IgA , whereas the concentration of IgM was shown to be increased by 43,11 % (p < 0,05) in irradiated animals. The decrease of IgA (by 16,29 %, p < 0,05) and IgG (by 32,66 %, p < 0,01) was an important criterion of the immunosuppressive action of radiation in humoral immunity. Irradiation had also a significant impact on the concentrations of CIC. As such, we identified a reliable decrease of 21.64 % (p < 0.05) in the blood serum of experimental rats.
Serious changes were observed in the nonspecific phagocytic immunity link in irradiated organisms. We observed a reduction of the phagocytic activity of blood cells by 17,31 % (p < 0,05) in irradiated experimental animals. The results of the calculation of the average number of latex absorbed by one phagocyte (phagocytic number) in the group of irradiated animals revealed a decrease by 9.35 % (p < 0.05).
Evaluating the oxygen-dependent phagocytic killing in the recovery test of NTT is known to serve as an indicator of the phagocytic and metabolic activity of neutrophilic granulocytes. A NTT-test might reflect the final reaction of one of the critical enzymatic systems responsible for the effector potential of phagocytes. Our study showed that the index of the NTT-test in experimentally irradiated animals was decreased by 13.12 % (p > 0.05), indicating a suppression of the functional activity of neutrophils. Collectively, the revealed tension of the phagocytic link in the form of the suppression of the phagocytic activity, reduction of the phagocytic number, and obtained NTT-test results in irradiated animals further testified for the immunodepressant effect of radiation.
Thus, we revealed a number of changes in experimental rats irradiated with gamma radiation, which were characterized, first of all, by a decrease of the absolute and percentile number of T-lymphocytes and their subpopulation (CD4+, CD8+), decrease in the functional activity of T-lymphocytes, and a decrease in the protective and adaptive mechanisms of the organism in response to the action of long term exposure to a high dose of radiation. The decrease in the quantity of CD3+ cells and their subpopulation, which are known to serve as the response of the immune system to developing pathological processes could be regarded as a general physiological response of an organism in response to a stress irritant [30]. However, there were also changes in qualitative and quantitative indicators of humoral and nonspecific phagocytic links of immunity, which constitute a fact of developed immunodeficiency of radiation genesis. Accordingly, we found that the proliferative activity of T-cells, and quantitative and functional states of the T-system of immunity were also decreased.
The analysis of the factual material showed that the suppressive action of gamma radiation on the immune system was preserved in the long term; suppression was detected not only on the T-cell link, but also on nonspecific phagocytic links, and on the functional-metabolic activity of neutrophils.