Immunoglobulin G Expression And Its Co-localization With Complement Proteins In Papillary Thyroid Cancer

Background and ObjectivesExcept for the well known immunoglobulin G (IgG) producing cell types, i.e. mature B lymphocytes and plasma cells, various non-lymphoid cell types, including human cancer cells, neurons, and some specified epithelial cells have been found to express immunoglobulin G. In this study, we detected that whether papillary thyroid cancer (PTC) cells can produce immunoglobulin G. And also we explored its producing mechanism and function. Furthermore, we detected the expression of complement proteins (C1q, C3c and C4c) in papillary thyroid cancer cells.Materials and Methods1 Tissue samples: Papillary thyroid cancer tissues were obtained from patients at Pathology Department of Shantou University Medical College between 2009 and 2010. In total, there were 44 patients, 40 females (90.1%), mean age: 45, 15 presence of lymph node (34.1%).2 Immunohistochemistry: PV-9000 universal two steps method was used to detect whether PTC cells express IgGγheavy chain, C1q, C3c, C4c and IgG Fc specific receptors (CD16, CD32, CD64 and FcRn).3 Generation of digoxigenin-labeled cRNA probes: Constant region of immunoglobulin G1 heavy chain (IGHG1) cRNA probe and complement 3 cRNA probe were generated.4 In Situ Hybridization: To detect the IGHG1 mRNA and C3 mRNA expression of PTC cells.5 Laser Capture Micro-dissection: To dissect the PTC cells from frozen sections. 6 Reverse Transcription Polymerase Chain Reaction: To detect IGHG1 mRNA, IgκmRNA, RAG1 mRNA, RAG2 mRNA and AID mRNA expression of the PTC cells.7 Evaluation of IgGγheavy chain expression: H-score was used to evaluate the IgGγheavy chain expression of tissue micro-array.8 Statistical analysis: The difference of H-score was assessed by the Mann-Whitney test. P < 0.05 for the difference was significant, P< 0.01 for the difference was highly significant.Results1 Immunohistochemistry: IgGγheavy chain, Igκlight chain, C1q, C3c and C4c expressed in the cytoplasm of PTC cells. 80% (35/44) of total samples studied, stained positive for IgGγheavy chain. 59% (26/44) were stained positive for Igκlight chain. We totally tested 20 samples for C1q, C3c and C4c. 60% were positive and located in the cytoplasm of PTC cells. Applying IHC on serial sections, we found that C1q, C3c and C4c were co-localized with IgGγheavy chain in the same PTC cells. And we did not detect the IgG specific Fc receptors in the PTC cells.2 In Situ Hybridization: IGHG1 mRNA was expressed in the cytoplasm of PTC cells. But C3 mRNA was not detected.3 LCM related RT-PCR: IGHG1, Igκ, RAG1, RAG2 and AID mRNA expressed in the PTC cells.4 Statistical analysis: IgGγheavy chain expression was correlated with tumor size. The tumor was bigger, the more IgGγwas expressed. The difference was significant. IgGγheavy chain expression in the PTC samples was significantly higher than it in normal thyroid tissues. The difference was highly significant. In addition, PTC with local lymph node metastases had higher H-score than PTC without lymph node metastases. The difference was significant. ConclusionWe established that PTC cells are capable of producing IgG. And it is suggested that IgG can enhance the growth and metastasis of PTC cells. Its co-localization with C1q, C3c and C4c suggests the presence of immune complexes. The formation of such immune complexes might protect the cancer cells from destruction by the complement system. It provides a new mechanism of tumorigenesis and may provide new experimental evidences for tumor diagnosis, therapy and prevention.