Objective:To investigate the expression change of human leukocyte antigen(HLA) class I on human peripheral blood mononuclear cells(PBMCs) at both mRNA and protein levels,and to evaluate its roles in the development of colorectal cancer(CRC).Methods:In the present study,50 patients with CRC,35 patients with benign colorectal lesion and 42 healthy volunteers were enrolled.Expression levels of HLA class I mRNA and protein were determined using real-time quantitative reverse transcription PCR(RT-PCR) and flow cytometry analysis,respectively.Results:The expression levels of HLA class I mRNA and proteins were not influenced by age and gender.The relative ratios of HLA class I mRNA were 0.99±0.27 in healthy controls,0.76±0.19 in benign patients,and 0.48±0.21 in CRC patients.Mean fluorescence intensities of HLA class I were 145.58±38.14 in healthy controls,102.05±35.98 in benign patients and 87.44±34.01 in CRC patients.HLA class I on PBMCs was significantly down-regulated at both mRNA and protein levels in patients with stage III and IV CRC.CRC patients with lymph node metastasis also showed a decreased HLA class I expression at protein level.Conclusion: HLA class I expressions on PBMCs are associated with staging of CRC and lymph node metastasis. Monitoring the expression of HLA class I on PBMCs may provide useful information for diagnosis and metastasis judgement of CRC. Objective: To investigate the expression change of human leukocyte antigen (HLA) class I on human peripheral blood mononuclear cells (PBMCs) at both mRNA and protein levels, and to evaluate its roles in the development of colorectal cancer (CRC). Methods: In the present study, 50 patients with CRC, 35 patients with benign colorectal lesion and 42 healthy volunteers were enrolled. Expression levels of HLA class I mRNA and protein were determined using real-time quantitative reverse transcription PCR (RT-PCR) and flow cytometry analysis , respectively. Results: The expression levels of HLA class I mRNA and proteins were not affected by age and gender. The relative ratios of HLA class I mRNA were 0.99 ± 0.27 in healthy controls, 0.76 ± 0.19 in benign patients, and 0.48 ± 0.21 in CRC patients. Mannich fluorescence intensities of HLA class I were 145.58 ± 38.14 in healthy controls, 102.05 ± 35.98 in benign patients and 87.44 ± 34.01 in CRC patients. HLA class I on PBMCs were significantly down-regulated at both mRNA an d protein levels in patients with stage III and IV CRC. CRC patients with lymph node metastasis also showed a decreased HLA class I expression at protein level. Confc: HLA class I expressions on PBMCs are associated with staging of CRC and lymph node metastasis. Monitoring the expression of HLA class I on PBMCs may provide useful information for diagnosis and metastasis judgment of CRC.