Apoptosis of intimal cells is an important contributor to the pathogenesis of
atherosclerosis and transplant
vascular disease (TVD). Since the activated immune response may be a key regulator of apoptosis in these lesions, we used immunohistochemistry to characterize the presence and localization of
granzyme B, a major mediator of the cytotoxic immune response, in advanced
atherosclerosis and TVD.
Formalin-fixed,
paraffin-embedded transverse sections from human left anterior descending coronary arteries were cut serially and stained with
antibodies specific for
granzyme B, smooth muscle
alpha-actin, CD68, and CD3. The amount of
granzyme B staining was semi-quantitated on a 0-5+/5+ scale. Also, TUNEL staining and in situ hybridization was performed to visualize cells undergoing cellular damage suggestive of apoptosis, and to localize
granzyme B mRNA, respectively.
Granzyme B localization was similar in both diseases. This
protease was absent in arteries with mild
atherosclerosis, but was abundant in the intima and media of vessels with advanced
atherosclerosis and TVD. Within the intima,
granzyme B localized to TUNEL-positive foam cells surrounding
lipid-rich
atheromas. Staining of serial sections with
granzyme B and either smooth muscle
alpha-actin, anti-CD68, or anti-CD3 showed that
granzyme B localized to smooth muscle cells, macrophages, and T-cells. Further, in situ hybridization for
granzyme B mRNA in TVD cases localized its expression to infiltrating leukocytes and not foam cells. In conclusion, the presence of
granzyme B in advanced atherosclerotic lesions and TVD is associated with increasing disease severity and cell death. These observations suggest that
granzyme B-mediated apoptosis may contribute to the pathogenesis of these diseases.