It is well known that the glucocorticoids have a suppressive activity to the immune
responses through various mechanisms. Among others, one of well explained suppression
mechanisms is that through lympholytic effects of the drugs on the lymphoid tissue
throughout the body. But the precise processes of lympholytic actions and the ultra-
structural changes during the cytolytic responses are largely remained in questions.
In the efforts of clarifying the morphologic changes of the lymphoid tissue after glu-
corticoid administration, the author studied the ultrastructural changes of the mesenteric
lymph nodes of rabbits after the injections of varying doses of prednisolone. Animals
were injected 5mg, 10mg and 20mg of prednisolone for three consecutive days,
repectively. On the fourth day, the animals were sarcrificed and observed.
The results were summarized as follow :
1. Light microscopically, the germinal center showed severe loss of large lymphocytes
and prominent increase of reticulum cells. Marked decrease of small lymphocytes were
also noted in TDA, while large lymphocytes were evidently increased in number in the
mdeulla.
2. Electron microscopically, the nuclei showed increased tendency of heterochromatin,
dilatation of perinuclear cisternae and condensation of chromatin to the degree of
pyknosis. Mitochondria were markedly atrophied, accompanying with increase of matrix
density and decrease of cristae. Increased number of pseudopodia with swelling was also
prominent. Other changes were decrease of ribosomes and dilatation of ER. These
changes were mostly confined to the small lymphocytes, and the other cellular
components did not show such changes. The changes of small lymphocytes were
progressively more severe with increasing the doses of the drug. The destructed cellular
debris were phagocytized within macrophages and reticulum cells.
3. These results suggest that the main cytolytic actions of prednisolone are exerted to
the small lymphocytes, preserving other cellular components, and the destucted cellular
debris are caught to the surrounding macrophages and reticulum cells,
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