Search

Except for the well-known immunoglobulin G (IgG) producing cell types, ie, 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 IgG. In this study, we detected the expression of the heavy chain of IgG (IgGγ) and kappa light chain (Igκ) in papillary thyroid cancer cells. Using in situ hybridization, we detected the constant region of human IgG1 (IGHG1) in papillary thyroid cancer cells. With laser capture microdissection followed by RT-PCR, mRNA transcripts of IGHG1, Igκ, recombination activating gene 1 (RAG1), RAG2, and activation-induced cytidine deaminase genes were successfully amplified from isolated papillary thyroid cancer cells. We further confirmed IgG protein expression with immunohistochemistry and found that none of the IgG receptors was expressed in papillary thyroid cancer. Differences in the level of IgGγ expression between tumor size, between papillary thyroid cancer and normal thyroid tissue, as well as between papillary thyroid cancer with and without lymph node metastasis were significant. Taken together, these results indicate that IgG is produced by papillary thyroid cancer cells and that it might be positively related to the growth and metastasis of papillary thyroid cancer cells. Furthermore, it was demonstrated that IgGγ colocalized with complement proteins in the same cancer cells, which could indicate that immune complexes were formed. Such immune complexes might consist of IgG synthesized by the host against tumor surface antigens and locally produced anti-idiotypic IgG with specificity for the variable region of these ‘primary’ antibodies. The cancer cells might thus escape the host tumor-antigen-specific immune responses, hence promoting tumor progression.

Except for the well-known immunoglobulin G (IgG) producing cell types, ie, 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 IgG. In this study, we detected the expression of the heavy chain of IgG (IgGγ) and kappa light chain (Igκ) in papillary thyroid cancer cells. Using in situhybridization, we detected the constant region of human IgG1 (IGHG1) in papillary thyroid cancer cells. With laser capture microdissection followed by RT-PCR, mRNA transcripts of IGHG1, Igκ, recombination activating gene 1(RAG1), RAG2, and activation-induced cytidine deaminasegenes were successfully amplified from isolated papillary thyroid cancer cells. We further confirmed IgG protein expression with immunohistochemistry and found that none of the IgG receptors was expressed in papillary thyroid cancer. Differences in the level of IgGγexpression between tumor size, between papillary thyroid cancer and normal thyroid tissue, as well as between papillary thyroid cancer with and without lymph node metastasis were significant. Taken together, these results indicate that IgG is produced by papillary thyroid cancer cells and that it might be positively related to the growth and metastasis of papillary thyroid cancer cells. Furthermore, it was demonstrated that IgGγcolocalized with complement proteins in the same cancer cells, which could indicate that immune complexes were formed. Such immune complexes might consist of IgG synthesized by the host against tumor surface antigens and locally produced anti-idiotypic IgG with specificity for the variable region of these ‘primary' antibodies. The cancer cells might thus escape the host tumor-antigen-specific immune responses, hence promoting tumor progression.

The placenta is known to protect the fetus from infection and maternal rejection. In a previous study, we demonstrated that placental trophoblasts can synthesize immunoglobulin G (IgG). In this study, we investigated the distribution of immunoglobulins (IgG, IgM, and IgA), IgG receptors (FcRn and FcgammaRIII), and complement proteins in placental trophoblasts at the ultrastructural level. In addition, we studied the mRNA expression of IgG1 heavy chain (IGHG1), recombination activating gene 1 (RAG1), RAG2, and activation-induced cytidine deaminase (AID) with nested RT-PCR in primary cultured trophoblasts. The mRNA transcripts of IGHG1, RAG1, RAG2, and AID were all identified in primary trophoblasts, further establishing the IgG-producing capacity of trophoblasts. At the ultrastructural level with colloidal gold-labeled antibodies, IgG was found to be distributed in two distinct locations in syncytiotrophoblasts. For one, it was colocalized with FcRn in endosome displaying low electron density, and for the other it was colocalized with complement C1q in medium-electron density irregular structures that have not been reported previously. This characteristic distribution suggests that IgG is likely processed through two molecular mechanisms in syncytiotrophoblasts: receptor-bound transportation across the syncytiotrophoblast and formation of immune complexes with locally produced IgG. The latter mechanism is probably aimed at neutralizing detrimental maternal anti-paternal major histocompatibility complex antibodies. Our findings support the hypothesis that placenta-produced IgG can selectively react with maternal anti-fetus antibodies and provide a mechanism of fetomaternal tolerance to protect the fetus from maternal immune rejection.