High expression of p21 Waf1 in sarcoid granulomas: a putative role for long-lasting inflammation.

In sarcoid granulomas, apoptotic events are reduced, which explains their characteristic long-lasting inflammation. We have described that interferon-gamma (IFN-gamma) inhibits apoptosis in macrophages through the expression of p21(Waf1). Here, we explore the molecular mechanisms involved in the inhibition of apoptosis in sarcoid granulomas. We analyzed skin biopsies from 19 sarcoidosis patients and 16 controls. Total RNA was subjected to semiquantitative reverse transcriptase-polymerase chain reaction analysis. There was no difference found in the expression of proapoptotic (Bax and Bcl-X(s)) or antiapoptotic (Bcl-2 and Bcl-X(L)) genes nor in the expression of the tumor suppressor gene p53. Furthermore, the expression of IFN-gamma and the cdk inhibitors p21(Waf1) and p27(Kip1) were analyzed. IFN-gamma was detected in 37% of the sarcoidosis patients, and controls were negative (P<0.02). In addition, a higher proportion of patients expressing p21(Waf1) (58%) versus controls (12%) was found (P<0.005). There was a significant correlation between the expression of IFN-gamma and p21(Waf1) (r=0.69) and between p21(Waf1) and fibronectin (r=0.65). Finally, using immunohistochemistry, high p21(Waf1) reactivity was observed inside the granuloma. We conclude that the high levels of p21(Waf1) in sarcoidosis may explain the absence of apoptosis in the granuloma and the persistence of inflammation.