might relate to auto-immunity
and possibly in turn to aging fui5].
There
were at the time few results on animals consistent with the hypothesis of a
breakdown in the balance of self-tolerance leading to auto-immune conditions,
and on the whole the data were thought to be inconclusive in showing positively any such effect.
ho,
Studies of the late effects of radiation on the immune system of mammals
are still relatively few and their results variable according to the test
system and radiation doses.
In general, intact animals examined individually
show little if any effect of age [S45]
reticular tissue tumours
[U14].
mostly correlated with the presence of
When the immune competence of cells from ir-
ratiated animals is examined, there is often a significant decrease in cell
number, but this appears to be well compensated by an increase in antibody
affinity A10].
ted.
Other immune functions could, however, be significantly effec-
Recent evidence about effects at the whole-body level is rather ambiguous.
On the other hand, animals selected for a low antibody response showed a higher
incidence of spontaneous malignancies and a shorter life-span than others of
the same genetic packground selected for a low response
[C30].
On the other
hand, total lymphoid irradiation performed on NZB/NZW mice with a high incidence of an auto-immune disease reversed the expression of this condition and
thus produced a prolongation of survival [K22].
50.
In comprehensive review of the immunological action of radiation Anderson
and Warner [A10] discussed three general hypotheses for the possible induction
or acceleration of auto-immune processes.
The first one considers that ra-
diation could alter tissue constituents to create new auto-antigens or to re-
lease previously inaccessible components.
The second possibility would act
via somatic mutations leading to the emergence of auto-reactive clones.
The
third would act through the unbalance of natural mechanisms of regulation con-
trolling the potential auto-immune expression.
Several studies would be in
favour of the third mechanism but at the present time few definitive statements are warranted.
D1.
The first statement might be that the interplay of regulatory mechanisms
in the immune system is so complex and variable that radiation effects are
hardly
predictable and at present cannot be extrapolated with any confidence
from one experimental situation to another.
Secondly, although immunological
mechanisms could actually be operating at high radiation exposures causing