Publication: lmmunohistochemical expression of p53, p21/waf1, Rb, p16, cyclin D1, p27, Ki67, cyclin A, cyclin B1, bcl2 bax
and bak proteins and apoptotic index in normal thymus
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Date
2001
Authors
Kanavaros, Panagiotis ; Stefanaki, K. ; Rontogianni, D. ; Papalazarou, D. ; Sgantzos, M. ; Arvanitis, D. ; Vamvouka, C. ; Gorgoulis, V. ; Siatitsas, I. ; Agnantis, N.J. ; Bai, M.
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Publisher
Murcia : F. Hernández
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DOI
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info:eu-repo/semantics/article
Description
Abstract
The immunohistochemical expression of
p53, p21, Rb, p16, cyclin D1, Ki67, cyclin A, cyclin B1,
p27, bc12, bax, and bak proteins and the apoptotic index
(AI) were investigated in 20 normal thymuses (8 adults,
3 adolescents, 5 infants and 4 newborns). The
expressions of Rb, Ki67, cyclin A and cyclin B1 were
overlapping, being high in the cortex with a tendency for
decreased expression toward the medulla. Apoptotic
cells were mainly detected in the cortex and the
corticomedullary junction, rarely being present in
Hassall's corpuscles. The mean values of Ki67, cyclin A,
and cyclin B1 expression in thymuses were 77.2%,
32.2% and 21.4% (newborns), 62.4%, 33.7% and 18.5%
(infants), 56.9%, 23.4% and 18.9% (adolescents) and
38.7%, 21.7% and 14.6% (adults), respectively. The
mean values of AI in thymuses from newborns, infants,
adolescents and adults were 1.4%, 2.9%, 2.7% and
3.8%, respectively. This decrease in proliferation and
increase in apoptosis may account for the process of
thymic involution. P16 expression was widespread with
most of Hassall's corpuscles being pl6-positive. P16-
positive cells and Hassall's corpuscles increased with the
increase in age, in keeping with the suggested role of
p16 in cellular senescence. P27 expression was
undetectable in subcapsular thymocytes with a tendency
for increased expression toward the medulla. The expressions of Ki67, cyclin A and cyclin R1 were
inversly related with that of p27, consistent with
previous evidence that p27 concentration is reduced
when the cell-cycle progresses. P21 and much less
frequently p53 proteins were mainly detected in a part of
the subcapsular cortical epithelial cells. These findings
suggest that a) in thymocytes, the apoptotic pathway is
mostly p53-independent and the function of p21 as a
negative regulator of the cell cycle must be redundant to
other negative regulators, such as p16 and p27 which were abundantly detected in thymocytes and b) in some
thymic epithelial cells, the p21 expression may be
induced by p53, but in most of them seems to be p53-
independent. Most of Hassall's corpuscles were p21-
positive, consistent with previous evidence that these
structures represent end stages of maturation of thymic
medullary epithelium and that p21 protein is involved in
the process of terminal differentiation. Cyclin D1
positivity was found in some macrophages. Rc12
expression was mainly seen in medullary thymocytes,
reflecting the surviving thymocytes in this region. The
expressions of Bax and bak were more widespread in
both the medulla and cortex, suggesting that these
proteins play a broader role than bc12 in the regulation of
thymic apoptosis.
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