THYMUS AS A POSSIBLE TARGET OF 50 HZ ELECTRIC AND MAGNETIC FIELDS (MEETING
ABSTRACT).

Capri, M.; Quaglino, D.
Dept. of Biomedical Sciences, General Pathology, Univ. of Modena, Modena,
Italy

Thymus is the central organ responsible for the production of
immunocompetent T cells. Thymocyte proliferation and maturation is achieved
as a consequence of the interactions with thymic stromal cells under the
control of several mediators, produced by thymic microenvironment. The aim
of this study was to investigate the effects of the exposure to extremely
low electro and magnetic fields (EMFs) on the rat thymus. Three different
experiments were performed: (1) Male Sprague Dawley rats, 2 mo old, were
housed in the CESI (Milan, Italy) under standard conditions in a dark-light
cycle. Animals were divided into 3 groups that were exposed or sham-exposed
to 50-Hz sinusoidal EMFs at 1 kV/m-5 uT and 5kV/m-100 uT, respectively.
Exposure was performed for 8 mo, 5 days/wk, 8 hr/day. At sacrifice, the
thymus was removed and processed for light and electron microscopy and for
flow cytometry. The expression of CD8-CD4-, CD8+CD4, CD8-CD4+, CD8+CD4+,
CD5+ alphabetaTCR- and CD5+alphabetaTCR+ thymocytes was investigated. A long
term exposure to EMF was associated with an enhanced cellular turnover as
suggested by the increased number of mitotic and apoptotic events, whereas
necrosis was only slightly modified; furthermore, collagen deposition was
frequently observed in the exposed animals. Interestingly, the effects of
the EMF appeared to be independent from the field strength, since major
changes were noted after lowest field intensity exposure. Structural
changes, however, were not sustained by significant changes in the
characteristics of maturation and/or differentiation of thymocytes, as
demonstrated by flow cytometry. (2) Male Sprague Dawley rats were exposed to
the same EMFs in the same environmental conditions as before. Animals were
exposed, (i) from the second day after conception up to 15, 30 and 90 days
after birth; (ii) from 2 mo up to 5 and 8 mo of age. Rats were killed by
decapitation and the thymus was removed and processed for
immunocytochemistry. The presence and distribution of interleukin-2 (IL-2)
and beta-endorphin positive cells in the rat thymus were investigated.
Results indicated that exposure to EMFs affects the presence of IL-2 and
beta-endorphin-positive cells in the thymus. At almost all exposure times,
the percentage of IL-2 positive cells appeared statistically diminished both
in the medulla and in the cortex, compared with age-matched unexposed
animals. Surprisingly, in the rats exposed from conception up to 90 days of
age to the lowest electromagnetic field intensity, an increase of IL-2
positive cells in the thymic cortex was observed. By contrast, the
percentage of beta-endorphin-positive cells decreased with time in almost
all groups of exposed rats, compared with sham-exposed animals of the same
age. However, a slight increase of beta-endorphin-positive cells was found
only in the cortex and in the medulla of rats exposed from conception up to
15 and 90 days of age. (3) Male Sprague Dawley rats 2 mo old, housed in the
CESI animal care facilities, were divided into 3 groups and exposed to the
same EMFs as before, but under continuous light. At sacrifice, thymus was
removed and processed for electron microscopy. Results showed that, in aged
and light-stressed animals, thymus rapidly diminishes in size, because of
massive death of cortical small lymphocytes and their destruction by
macrophages; however, the concomitant exposure to EMF, especially at the
lowest field strength, was associated with increased cellular turnover, as
suggested by the augmented number of mitotic and apoptotic events, and with
increased collagen deposition. On the contrary, nuclear degenerations and
necrotic areas were more frequently observed in animate exposed to the
higher field strength, which therefore caused more pronounced degenerative
features. In conclusion, these data contributing to the understanding of the
interactions between EMFs and biological systems suggest that: (i) EMF
exposure can interfere with the structural characteristics and/or tissutal
organization of the thymus without altering, however, the phenotypic
features of thymocytes; (ii) the biological effects are exerted
independently from field strength and are conceivable with the existence of
window effects; (iii) EMFs are able to modulate the amount of IL-2 and
beta-endorphin in thymic cells; (iv) EMFs may reinforce the alterations due
to a stress condition (i.e. continuous light) acting in a synergistic manner
and determining a more rapid involution of the thymus which might be
responsible for an increased susceptibility to the potentially hazardous
effects of EMF.

Valdemar Gísli Valdemarsson
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