| Purpose:Antigen-specific activation and proliferation of T lymphocytes are regulated by both positive and negative signals from the B7 family of costimulatory molecules. B7-H1 and B7-H4 have been identified in the past years. The two molecules play important roles in regulating T cell responses. However, there are few experiments about the role that B7-H1 and B7-H4 act on the tumor cells. Therefore, we investigate the expression of B7-H1 and B7-H4 in human colon and rectal carcinoma tissues.There is ample evidence indicating that costimulatory function of B7-H1 is not mediated through PD-1, a known receptor for B7-H1. Nevertheless, the costimulatory receptor for B7-H1 has not been identified unequivocally up to now. So we go in for the second receptor that is involved in the costimulatory function of B7-H1 other than PD-1.Methods:The expression of B7-H1 and B7-H4 molecules were examined by SP immunohistochemical staining in 60 cases of colon and rectal carcinoma specimens. Furthermore, the relationship between the expression and the clinicopathological features were analyzed.The T7 phage display cDNA library from human T lymphocytes was constructed. B7-H1Ig was coated in 96-well ELISA plates as the target protein, and then the T lymphocyte T7 phage display cDNA library was used to screen the binding protein or peptide. Results:1. In the 60 cases of tumor specimens, B7-H1 and B7-H4 were expressed highly and observed in the cell membrane, cytoplasm, or both. But, there was no significant expression of B7-H1 and B7-H4 in normal colon and rectal epithelium.2. In the 60 cases of colon and rectal carcinoma tissues, the expression rate of B7-H1 was 60%. The expression of B7-H1 increased from normal colon and rectal epithelium to colon and rectal carcinoma cell with significant difference(P<0.01). There was no correlation between the expression level of B7-H1 and the sex, age, histological types, grade and state(P>0.05), but significant correlation could be demonstrated with lymph node metastasis(P<0.01).3.B7-H4 was expressed highly in the 60 cases of colon and rectal carcinoma tissues. The expression rate of B7-H4 was 83.3%. Furthermore, the expression of B7-H4 was significantly correlated with lymph node metastasis(P<0.05), but not age, sex, histological types, grade and state(P>0.05).4. The experimental results showed that the titer of the T lymphocyte T7 phage display cDNA library was 2×107 pfu/ml. The phage titer of the amplified library was 4×1010 pfu/ml. Meanwhile, the cDNA fragments with the range of 300～2000bp in length were 92% of 100 randomly selected clones.5.The binding protein or peptide that interacted with B7-H1Ig had not been found yet.Conclusions:1.B7-H1 and B7-H4 overexpressed in colon and rectal carcinoma play certain roles in oncogenesis and progression of human colon and rectal carcinoma and in the evasion of tumor immunity.2. The expression of B7-H1 and B7-H4 in colorectal cancer is only correlated with lymph node metastasis, independent of age, sex, tumor histological types, grade and state.3.B7-H1 and B7-H4 are expressed highly in colon and rectal carcinoma, while low expression rate in normal colon and rectal epithelium. As a result, the two costimulatory molecules turn into the possible prognostic markers and new targets of immunotherapy for colon and rectal carcinoma.4. The T7 phage display library was successfully constructed with cDNA of T lymphocyte from human peripheral blood. We did the groundwork for further study the second receptor for B7-H1.
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