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.