The purpose of this study was to determine the localization of Bcl-2 protei
n in the human cornea. Antihuman Bcl-2 monoclonal antibodies (MAbs) against
selective Bcl-2 peptide sequences were used to localize Bcl-2 protein immu
nocytochemically in fresh eye bank donor human corneas (n = 4). Specificity
of each MAb was determined by Western blot analysis of pooled protein extr
acted from human corneal epithelium (n = 3). Expression of Bcl-2 protein in
apoptotic surface epithelial cells was detected by co-labeling with TUNEL
assay and anti-Bcl-2 antibody staining. Two MAbs specific for amino acids r
esidues (aa) 41-54 within the loop domain of Bcl-2 protein stained nuclei o
f all corneal epithelial cell layers. MAb specific for aa 61-76, also withi
n the loop domain, produced faint nuclei and nuclear envelope staining. Occ
asional corneal surface epithelial cells however, consistently lacked anti-
Bcl-2 nuclear staining with these three MAbs; concomitant TUNEL assay revea
led that all TUNEL positive-surface cells were Bcl-2 negative. In the strom
a, keratocytes showed similar but weak anti-Bcl-2 staining, All corneal end
othelial cells showed intense nuclear staining with MAbs, with no gradient
or absence of staining, In summary, Bcl-2 protein can be localized to the n
uclei and nuclear envelope of corneal epithelial cells, keratocytes and end
othelial cells with the use of MAbs specific for the loop domain of Bcl-2.
TUNEL-labeled surface epithelial cells did not stain with MAbs to Bcl-2, su
ggesting degradation or epitope masking perhaps by specific phosphorylation
of the loop domain during apoptosis, Taken together, these findings sugges
t that Bcl-2 protein may play a critical role in modulating apoptotic cell
desquamation in the human corneal epithelium. (C) 2001 Academic Press.