Immunohistochemical characterization of Fas (CD95) and Fas Ligand (FasL-CD95L) expression in the injured brain: Relationship with neuronal cell death and inflammatory mediators
Traumatic brain injury causes progressive
tissue atrophy and consequent neurological dysfunction,
resulting from neuronal cell death in both animal models
and patients. Fas (CD95) and Fas ligand (FasL/CD95L)
are important mediators of apoptosis. However, little is
known about the relationship between Fas and FasL and
neuronal cell death in mice lacking the genes for
inflammatory cytokines. In the present study, double
tumor necrosis factor/lymphotoxin-a knockout (–/–) and
interleukin-6–/– mice were subjected to closed head
injury (CHI) and sacrificed at 24 hours or 7 days postinjury.
Consecutive brain sections were evaluated for Fas
and FasL expression, in situ DNA fragmentation
(terminal deoxynucleotidyl transferase-mediated dUTPbiotin
nick end-labeling; TUNEL), morphologic
characteristics of apoptotic cell death and leukocyte
infiltration. A peak incidence of TUNEL positive cells
was found in the injured cortex at 24 hours which
remained slightly elevated at 7 days and coincided with
maximum Fas expression. FasL was only moderately
increased at 24 hours and showed maximum expression
at 7 days. A few TUNEL positive cells were also found
in the ipsilateral hippocampus at 24 hours. Apoptotic,
TUNEL positive cells mostly co-localized with neurons
and Fas and FasL immunoreactivity. The amount of accumulated polymorphonuclear leukocytes and CD11b
positive cells was maximal in the injured hemispheres at
24 hours. We show strong evidence that Fas and FasL
might be involved in neuronal apoptosis after CHI.
Furthermore, Fas and FasL upregulation seems to be
independent of neuroinflammation since no differences
were found between cytokine–/– and wild-type mice