Christine Korteweg

Expression and distribution of immunoglobulin G and its receptors in the human nervous system.

Recently, accumulating evidence has shown that several immunological molecules previously thought to be exclusively expressed by immune cells are also produced by nervous cells. Such molecules are thought to participate in the cross-talk between the immune and the nervous systems. IgG, an important immunological molecule, was traditionally thought to be produced by B lymphocytes only. In this study, extensive expression of neuron-derived IgG was detected throughout the nervous system. Relative quantification indicated that IgG was produced by neural cells at a low constant level. Transcripts of rearranged V-(D)-J segments and recombination activating genes-1 and -2 were also detected. Various IgG receptor types were also detected with distinct distribution patterns at different parts of the central and the peripheral nervous system. Given the widespread expression of IgG and its receptors, IgG most likely has an important biological function in the nervous system and might be classified as an immune mediator involved in neuro-immune crosstalk.

Expression and distribution of immunoglobulin G and its receptors in an immune privileged site: the eye

It has recently been demonstrated that not only mature B lymphocytes, but also non-lymphoid cells, including cancer cells and neurons, express IgG. In the eye, an important immune privileged site, the presence of IgG has been ascribed to IgG entering the eye through breaches of the blood–ocular barrier. Here we demonstrate that the eye itself can produce IgG intrinsically. Applying immunohistochemistry, in situ hybridization, and RT-PCR, several intraocular structures were found to express proteins and mRNA transcripts of IgG heavy chains, light chains, V(D)J rearrangements, and enzymes required for V(D)J recombination. IgG receptors were also detected in the intraocular epithelium and endothelium. The extensive distribution of IgG and its receptors in intraocular structures indicates that locally produced IgG could play a significant role in maintaining the ocular microenvironment and protection of the eyes, and it might also be involved in the pathogenesis of age-related macular degeneration and some inflammatory diseases.

Immunoglobulin G expression and its colocalization with complement proteins in papillary thyroid cancer

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.

IgG Expression in Human Colorectal Cancer and Its Relationship to Cancer Cell Behaviors

Increasing evidence indicates that various cancer cell types are capable of producing IgG. The exact function of cancer-derived IgG has, however, not been elucidated. Here we demonstrated the expression of IgG genes with V(D)J recombination in 80 cases of colorectal cancers, 4 colon cancer cell lines and a tumor bearing immune deficient mouse model. IgG expression was associated with tumor differentiation, pTNM stage, lymph node involvement and inflammatory infiltration and positively correlated with the expressions of Cyclin D1, NF-κB and PCNA. Furthermore, we investigated the effect of cancer-derived IgG on the malignant behaviors of colorectal cancer cells and showed that blockage of IgG resulted in increased apoptosis and negatively affected the potential for anchor-independent colony formation and cancer cell invasion. These findings suggest that IgG synthesized by colorectal cancer cells is involved in the development and growth of colorectal cancer and blockage of IgG may be a potential therapy in treating this cancer.

IgG gene expression and its possible significance in prostate cancers

In spite of recent advances in treatment strategies, prostate cancer (PCa) remains the second leading cause of cancer death in men with its genetic and biologic behaviors still poorly understood. Recently, accumulating evidence indicates that cancer cells, as well as some normal cells can secret IgG. This study was designed to evaluate IgG gene expression and its possible significance in PCa tissue samples and cell lines.

Transcription Factors E2A, FOXO1 and FOXP1 Regulate Recombination Activating Gene Expression in Cancer Cells

It has long been accepted that immunoglobulins (Igs) were produced by B lymphoid cells only. Recently Igs have been found to be expressed in various human cancer cells and promote tumor growth. Recombination activating gene 1 (RAG1) and RAG2, which are essential enzymes for initiating variable-diversity-joining segment recombination, have also been found to be expressed in cancer cells. However, the mechanism of RAG activation in these cancer cells has not been elucidated. Here, we investigated the regulatory mechanism of RAG expression in four human cancer cell lines by analyzing transcription factors that induce RAG activation in B cells. By RT-PCR, Western blot and immunofluorescence, we found that transcription factors E2A, FOXO1 and FOXP1 were expressed and localized to the nuclei of these cancer cells. Over-expression of E2A, FOXO1 or Foxp1 increased RAG expression, while RNA interference of E2A, FOXO1 or FOXP1 decreased RAG expression in the cancer cells. Chromatin immunoprecipitation experiments showed acetylation of RAG enhancer (Erag) and E2A, FOXO1 or FOXP1 were bound to Erag in vivo. These results indicate that in these cancer cells the transcription factors E2A, FOXO1 and FOXP1 regulate RAG expression, which initiates Ig gene rearrangement much in the way similar to B lymphocytes.

Immunoglobulin G (IgG) Expression in Human Umbilical Cord Endothelial Cells

Traditional views hold that immunoglobulin G (IgG) in the human umbilical cord is internalized by human umbilical endothelial cells for passive immunity. In this study, the protein and mRNA transcripts of IgG were found in the cytoplasm of human umbilical endothelial cells by immunohistochemistry, in situ hybridization, and reverse transcription PCR (RT-PCR). The essential enzymes for IgG synthesis and assembling, RAG1 (recombination activating gene 1), RAG2, and variable (V), diversity (D), and joining (J) segments for recombination of IgG, were also found in these cells by RT-PCR and real-time PCR. These results indicate that umbilical endothelial cells are capable of synthesizing IgG with properties similar to those of immune cells and that they may play additional roles besides lining the vessels and transporting IgG.

Expression and distribution of immunoglobulin G in the normal liver, hepatocarcinoma and postpartial hepatectomy liver

The liver has the extraordinary properties of regeneration and immune tolerance; however, the mechanisms governing these abilities are poorly understood. To address these questions, we examined the possible expression of immunoglobulins in the human and rat liver and the relationship of IgG expression to hepatocyte proliferation, metastasis, apoptosis and immune tolerance. Immunohistochemistry, in situ hybridization, laser-guided microdissection and reverse transcription-PCR were performed to examine the expression of IgG in normal human and rat liver, severe combined immunodeficient mouse (SCID) liver and human liver cancers and corresponding cell lines. Small interfering RNA (siRNA) was transfected into cultured hepatocarcinoma cells to downregulate the expression of IgG heavy chain genes. Cell proliferation and apoptosis were assayed with flow cytometry. Cell metastasis was assayed with a Transwell cell assay. Partial hepatectomy (70%) was performed in rats to examine the relationship between hepatocyte IgG and hepatocyte proliferation. IgG, together with essential enzymes for its synthesis, were expressed in the cytoplasm of hepatocytes of normal adult human and hepatoma patients and rat livers, SCID mouse liver and BRL-3A, L-02 and HepG-2 cell lines. Downregulation of IgG inhibited cell proliferation and metastasis and promoted apoptosis. Postsurgery livers expressed significantly more IgG than the livers before surgery and decreased to the original levels when hepatocytes stopped regeneration. IgA and IgM but not IgD and IgE were also positive in hepatocytes. Our findings demonstrate that normal and malignant hepatocytes are capable of synthesizing immunoglobulin, which has important roles in hepatocyte proliferation, apoptosis and cancer growth with profound clinical implications.

Immunoglobulin G Locus Events in Soft Tissue Sarcoma Cell Lines

Recently immunoglobulins (Igs) have been found to be expressed by cells other than B lymphocytes, including various human carcinoma cells. Sarcomas are derived from mesenchyme, and the knowledge about the occurrence of Ig production in sarcoma cells is very limited. Here we investigated the phenomenon of immunoglobulin G (IgG) expression and its molecular basis in 3 sarcoma cell lines. The mRNA transcripts of IgG heavy chain and kappa light chain were detected by RT-PCR. In addition, the expression of IgG proteins was confirmed by Western blot and immunofluorescence. Immuno-electron microscopy localized IgG to the cell membrane and rough endoplasmic reticulum. The essential enzymes required for gene rearrangement and class switch recombination, and IgG germ-line transcripts were also identified in these sarcoma cells. Chromatin immunoprecipitation results demonstrated histone H3 acetylation of both the recombination activating gene and Ig heavy chain regulatory elements. Collectively, these results confirmed IgG expression in sarcoma cells, the mechanism of which is very similar to that regulating IgG expression in B lymphocytes.

Two Ultrastructural Distribution Patterns of Immunoglobulin G in Human Placenta and Functional Implications

ABSTRACT 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.