Relationship of Bcl-2 expression with apoptosis and proliferation in colonic graft versus host disease

Graft versus host disease (GVHD) occurs in up to 75% of patients who have had an allogeneic bone marrow transplant (BMT). However, the pathophysiology of this disorder, including the mechanisms responsible for enhanced apoptosis, are poorly understood. Bcl-2 is a cellular protein known to inhibit apoptosis in a variety of human tissues. Therefore, the aim of this study was to evaluate the expression of Bcl-2 in colonic GVHD and to determine its relationship to cell proliferation and apoptosis in this disease. Routinely processed colonic mucosal biopsy specimens from 47 allogeneic BMT patients with diarrhea were evaluated histologically for the grade of GVHD (0-4) and for the degree of apoptosis (apoptosis index). Immunohistochemical staining for Bcl-2 and MIB-1, a cell proliferation marker, was performed, and the results were correlated with the histological findings and with each other. Normal-appearing colonic mucosal biopsy specimens from 10 age-matched patients with noncolonic diarrhea served as controls. Also evaluated were 13 colonic biopsy specimens from 13 patients with chronic ulcerative colitis (three inactive, four mild chronic-active, six moderately severe chronic active) to test the specificity of our findings. When compared with controls, a slight trend toward increased Bcl-2 expression was noted in patients with high-grade GVHD (grade 3 or 4) (P=.09). However, Bcl-2 expression did not correlate with the degree of apoptosis in these patients. In contrast, the degree of Bcl-2 staining correlated positively with the crypt proliferative rate (P=.04). Furthermore, crypt proliferation was significantly higher in the GVHD patients in comparison with controls (MIB-1 index, 27.7+/-17.1 v 15.6+/-11.4, =.02), and increased progressively with each successively higher grade of GVHD, and with the degree of apoptosis. Similar to GVHD, Bcl-2 expression was increased in biopsy specimens of CUC patients with higher grades of active injury and epithelial regeneration. This immunohistochemical study does not provide support for Bcl-2 in the pathogenesis of GVHD-induced apoptosis in the colon, but instead, indicates that this protein may play a nonspecific role in the generalized response to cellular injury in GVHD.