Objective To analyze the distribution of T lymphocyte subsets in tumor microenvironment of papillary thyroid carcinoma (PTC). Methods The levels of CD3+ CD4+ CD8- ,CD3+ CD4- CD8+ ,CD3+ CD4+ CD8+ ,CD3+ CD4- CD8- T cell and CD4+/CD8+ ra- tio in tumor microenvironment of 35 cases PTC, 25 cases benign thyroid lesion and 15 healthy eases were detected by flow cytometry. Results Local tumor tissue of 35 cases PTC and 25 cases benign thyroid lesion, and blood of 15 healthy cases were collected. The ratio of CD4+/ CD8+ in blood, tumor microenvironment of benign thyroid lesions and PTCs decreased significantly ( P<0.01). The levels of CD3+ CD4+ CD8+ cell in tumor microenvironment of PTC and benign thyroid lesion were higher than that in peripheral blood( P<0.01). But the differ- ence of the level of CD3+ CD4+ CD8+ cell between PTC and benign thyroid lesion was not significant ( P>0.05). The levels of CD3+ CD4- CD8- cell in tumor microenvironment of benign thyroid lesion were higher than those in PTC and peripheral blood(P<0.01). The difference of the level of CD3+ CD4- CD8- cell between PTC and peripheral blood was not significant (P>0.05 ). The differences of CD4+/CD8+ ratio and the level of each of T lymphocyte subset such as CD3+ CD4+ CD8-, CD3+ CD4- CD8+, CD3+ CD4+ CD8+, CD3+ CD4- CD8- cell between 15 PTC cases with lymph node metastasis and 20 PTC cases without metastasis were not significant (P>0.05). Conclusions CD8+ T cell is the main immune cell in tumor microenvironment in PTC. The local cell-mediated immunity of PTC is in the status of obviously suppressed. But the obvious increase of CD3+ CD4+ CD8+ and CD3+ CD4- CD8- T cells in tumor microenvironment in thyroid benign lesion may be beneficial for creating the location for immune responding against tumor. The distribution of T lymphocyte sub- sets in tumor microenvironment in PTC is not associated with lymph node metastasis.

0.05).Conclusions The local cell-mediated immunity of PTC is in the status of obviously suppressed.But the local impaired immune response against carcinoma is not associated with lymph node metastasis of PTC.