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

Genetic Characteristics of Non B Cell-Derived Immunoglobulin Genes

It is widely acknowledged that immunoglobulins (Igs) are produced solely by B-lineage cells. The Ig gene is created by the rearrangement of a group of gene segments [variable (V), diversity (D), and joining (J) segments rearrangement, or V(D)J recombination], which results in the vast diversity of B cell-derived Ig responsible for recognising various antigens. Ig subsequently undergoes somatic hypermutation (SHM) and class switch recombination (CSR) after exposure to antigens, thus converting the low-affinity IgM to IgG, IgA, or IgE antibodies. IgM and IgD are primarily expressed in naïve B cells that have not been exposed to antigens, they do not undergo somatic hypermutation; hence, their variable region sequences remain the same as those in the germline. In contrast, IgG, IgA, and IgE are expressed in antigen-stimulated memory B cells or plasma cells, and thus, they often possess high-frequency mutations in their variable region sequences. Since the discovery that Ig can be produced by non-B cells, Qiu's group has investigated and compared the genetic characteristics of B cell-derived Ig and non-B cell-derived Ig. These findings demonstrated that non-B cell-derived Ig shares certain similarities with B cell-derived Ig in that the sequence of its constant region is identical to that of B cell-derived Ig, and its variable region is also strictly dependent on the rearrangement of V, D, and J gene segments. Moreover, akin to B cell-derived Ig, the V regions of IgM and IgD are rarely mutated, while IgG, IgA, and IgE produced by cancer cells are frequently mutated. However, the non-B cell-derived Ig V region sequence displays unique characteristics. (1) Unlike the vast diversity of B cell-derived Igs, non-B cell-derived Igs exhibit restricted diversity; cells from the same lineage always select the same V(D)J recombination patterns; (2) Both mRNA and proteins of RAG1/RAG2 recombinase have been detected in Ig positive cancer cell lines and normal tissues. But Ig recombination could also be found in RAG1-/- and RAG2-/- mice, suggesting that they are not necessary for the rearrangement of non-B cell-derived Igs. These features of non-B cell-derived Igs suggest a potentially undiscovered mechanism of V(D)J recombination, ligation, and SHM in non-B cells, which necessitates further investigation with advanced technology in molecular biology.

Expression and Clinical Significance of Non B Cell-Derived Immunoglobulins in the Urinary System and Male Reproductive System

The urinary system comprises kidneys, ureters, bladder, and urethra with its primary function being excretion, referring to the physiological process of transporting substances that are harmful or surplus out of the body. The male reproductive system consists of gonads (testis), vas deferens, and accessory glands such as the prostate. According to classical immunology theory, the tissues and organs mentioned above are not thought to produce immunoglobulins (Igs), and any Ig present in the relevant tissues under physiological and pathological conditions is believed to be derived from B cells. For instance, most renal diseases are associated with uncontrolled inflammation caused by pathogenic Ig deposited in the kidney. Generally, these pathological Igs are presumed to be produced by B cells. Recent studies have demonstrated that renal parenchymal cells can produce and secrete Igs, including IgA and IgG. Glomerular mesangial cells can express and secrete IgA, which is associated with cell survival and adhesion. Likewise, human podocytes demonstrate the ability to produce and secrete IgG, which is related to cell survival and adhesion. Furthermore, renal tubular epithelial cells also express IgG, potentially involved in the epithelial-mesenchymal transition (EMT). More significantly, renal cell carcinoma, bladder cancer, and prostate cancer have been revealed to express high levels of IgG, which promotes tumour progression. Given the widespread Ig expression in the urinary and male reproductive systems, continued efforts to elucidate the roles of Igs in renal physiological and pathological processes are necessary.

The Expression of Non B Cell-Derived Immunoglobulins

Although V(D)J recombination and immunoglobulin (Ig) production are traditionally recognised to occur only in B lymphocytes and plasma cells, the expression of Igs in non-lymphoid cells, which we call non B cell-derived Igs (non B Igs), has been documented by growing studies. It has been demonstrated that non B-Igs can be widely expressed in most cell types, including, but not limited to, epithelial cells, cardiomyocytes, hematopoietic stem/progenitor cells, myeloid cells, and cells from immune-privileged sites, such as neurons and spermatogenic cells. In particular, malignant tumour cells express high level of IgG. Moreover, different from B-Igs that mainly localised on the B cell membrane and in the serum and perform immune defence function mainly, non B-Igs have been found to distribute more widely and play critical roles in immune defence, maintaining cell proliferation and survival, and promoting progression. The findings of non B-Igs may provide a wealthier breakthrough point for more therapeutic strategies for a wide range of immune-related diseases.

Comparison of Non B-Ig and B-Ig

Immunoglobulin (Ig) has been widely acknowledged to be produced solely by B-lineage cells. However, growing evidence has demonstrated the expression of Ig in an array of cancer cells, as well as normal cells including epithelial cells, epidermal cells, mesangial cells, monocytes, and neutrophils. Ig has even been found to be expressed in non-B cells at immune-privileged sites such as neurons and spermatogenic cells. Despite these non-B cell-derived Igs (non-B-Igs) sharing the same symmetric structures with conventional Igs (B-Igs), further studies have revealed unique characteristics of non-B-Ig, such as restricted variable region and aberrant glycosylation. Moreover, non-B-Ig exhibits properties of promoting malignant behaviours of cancer cells, therefore it could be utilised in the clinic as a potential therapeutic biomarker or target. The elucidation of the generation and regulation of non-B-Ig will certainly broaden our understanding of immunology.

Oocytes could rearrange immunoglobulin production to survive over adverse environmental stimuli

Immunoglobulins are key humoral immune molecules produced and secreted by B lymphocytes at various stages of differentiation. No research has reported whether immunoglobulins are present in the non-proliferative female germ cells—oocytes—and whether they are functionally important for oocyte quality, self-protection, and survival. Herein, we found that IgG was present in the oocytes of immunodeficient mice; the IgG-VDJ regions were highly variable between different oocytes, and H3K27Ac bound and regulated the IgG promoter region. Next, IgG mRNA and protein levels increased in response to LPS, and this increment was mediated by CR2 on the oocyte membrane. Finally, we revealed three aspects of the functional relevance of oocyte IgG: first, oocytes could upregulate IgG to counteract the increased ROS level induced by CSF1; second, oocytes could upregulate IgG in response to injected virus ssRNA to maintain mitochondrial integrity; third, upon bacterial infection, oocytes could secrete IgG, subsequently encompassing the bacteria, thus increasing survival compared to somatic cells. This study reveals for the first time that the female germ cells, oocytes, can independently adjust intrinsic IgG production to survive in adverse environments.

Exploring the Origin and Physiological Significance of DNA Double Strand Breaks in the Developing Neuroretina

Genetic mosaicism is an intriguing physiological feature of the mammalian brain that generates altered genetic information and provides cellular, and prospectively functional, diversity in a manner similar to that of the immune system. However, both its origin and its physiological significance remain poorly characterized. Most, if not all, cases of somatic mosaicism require prior generation and repair of DNA double strand breaks (DSBs). The relationship between DSB generation, neurogenesis, and early neuronal cell death revealed by our studies in the developing retina provides new perspectives on the different mechanisms that contribute to DNA rearrangements in the developing brain. Here, we speculate on the physiological significance of these findings.

SIA-IgG confers poor prognosis and represents a novel therapeutic target in breast cancer

The incidence rate of breast cancer is the highest in the world, and major problem in the clinical treatment is the therapy resistance of breast cancer stem cells (CSCs). Thus, new therapeutic approaches targeting breast CSCs are needed. Our previous study demonstrated cancer-derived sialylated IgG (SIA-IgG) is highly expressed in cancer cells with stem/progenitor features. Furthermore, a high frequency of SIA-IgG in breast cancer tissue predicted metastasis and correlated with poor prognosis factors, and depletion of IgG in breast cancer leads to lower malignancy of cancer cells, suggesting SIA-IgG could be a potential therapeutic target in breast cancer. In this study, we first investigated the relationship of SIA-IgG expression with the clinicopathological characteristics and clinical prognosis of breast carcinoma patients, and the data confirmed that the expression of SIA-IgG confers poor prognosis in breast cancer. Successively, by using a monoclonal antibody specifically against SIA-IgG, we targeted SIA-IgG on the surface of MDA-MB-231 cells and detected their functional changes, and the results suggested SIA-IgG to be a promising antibody therapeutic target in breast cancer. In addition, we explored the mechanism of action at the molecular level of SIA-IgG on breast cancer cell, the findings suggest that SIA-IgG promotes proliferation, metastasis, and invasion of breast cancer cells through the Wnt/β-catenin signaling pathway. Developing therapeutic antibody needs effective therapeutic target, and the antibody should better be a monoclonal antibody with high affinity and high specificity. This study provides a potential prognostic marker and a novel therapeutic target for breast cancer.

A Review of Emerging Tear Proteomics Research on the Ocular Surface in Ocular Allergy

Ocular allergy is an immunoglobulin E-mediated Type I hypersensitivity reaction localised to the ocular surface and surrounding tissues. Primary signs and symptoms of ocular allergy include itching, redness, irritation and inflammation. Eye-rubbing caused by itching has been shown to alter ocular surface protein concentrations in conditions linked to ocular allergy such as keratoconus. In keratoconus, the cornea begins to thin and sag over time, leading to progressive vision loss and blindness in severe conditions. Due to the high incidence of ocular allergy sufferers rubbing their eyes in response to symptoms of itching, the protein landscape of the ocular surface may be significantly altered. Differential protein expression caused by long-term inflammation and eye-rubbing may lead to subsequent changes in ocular surface structure and function over time. This review aims to summarise and explore the findings of current ocular allergy proteome research conducted using techniques such as gel electrophoresis, mass spectrometry and lab-on-a-chip proteomics. Proteins of interest for this review include differentially expressed immunoglobulins, mucins, functional proteins, enzymes and proteins with previously uncharacterised roles in ocular allergy. Additionally, potential applications of this research are addressed in terms of diagnostics, drug development and future research prospects.

Naturally Acquired Antibodies against Plasmodium falciparum: Friend or Foe?

Antibodies are central to acquired immunity against malaria. Plasmodium falciparum elicits antibody responses against many of its protein components, but there is also formation of antibodies against different parts of the red blood cells, in which the parasites spend most of their time. In the absence of a decisive intervention such as a vaccine, people living in malaria endemic regions largely depend on naturally acquired antibodies for protection. However, these antibodies do not confer sterile immunity and the mechanisms of action are still unclear. Most studies have focused on the inhibitory effect of antibodies, but here, we review both the beneficial as well as the potentially harmful roles of naturally acquired antibodies, as well as autoantibodies formed in malaria. We discuss different studies that have sought to understand acquired antibody responses against P. falciparum antigens, and potential problems when different antibodies are combined, such as in naturally acquired immunity.

Expression of immunoglobulin G in human proximal tubular epithelial cells

Proximal tubular epithelial cells (PTECs) have innate immune characteristics, and produce proinflammatory factors, chemokines and complement components that drive epithelial‑mesenchymal transition (EMT). Our previous studies revealed that human mesangial cells and podocytes were able to synthesize and secrete immunoglobulin (Ig)A and IgG, respectively. The aim of the present study was to evaluate the expression of Igs in PTECs. Firstly, IgG was detected in the cytoplasm, the cell membrane and the lumen of PTECs in the normal renal cortex by immunohistochemistry. Secondly, Igγ gene transcription and V(D)J recombination were detected in single PTECs by nested PCR and Sanger sequencing. Thirdly, Igγ, Igκ and Igλ were clearly detected in an immortalized PTEC line (HK‑2) by immunostaining and western blotting, in which RP215 (an antibody that predominantly binds to non‑B cell‑derived IgG) was used. In addition, Igγ, Igκ and Igλ gene transcripts, conservative V(D)J recombination in the Igγ variable region, recombination activating gene 1/2 and activation‑induced cytidine deaminase were all detected in HK‑2 cells. These data suggested that PTECs may express IgG in a similar manner to B cells. Furthermore, IgG expression was upregulated by TGF‑β1 and may be involved in EMT.

Single-Cell Sequencing Confirms Transcripts and VHDJH Rearrangements of Immunoglobulin Genes in Human Podocytes

Most glomerular diseases are associated with inflammation caused by deposited pathogenic immunoglobulins (Igs), which are believed to be produced by B cells. However, our previous study indicated that the human podocyte cell line can produce IgG. In this study, we aimed to confirm the transcripts and characterize the repertoires of Igs in primary podocytes at single cell level. First, single-cell RNA sequencing of cell suspensions from “normal” kidney cortexes by a 10xGenomics Chromium system detected Ig transcripts in 7/360 podocytes and Ig gene segments in 106/360 podocytes. Then, we combined nested PCR with Sanger sequencing to detect the transcripts and characterize the repertoires of Igs in 48 single podocytes and found that five classes of Ig heavy chains were amplified in podocytes. Four-hundred and twenty-nine V_HDJ_H rearrangement sequences were analyzed; podocyte-derived Igs exhibited classic V_HDJ_H rearrangements with nucleotide additions and somatic hypermutations, biased VH1 usage and restricted diversity. Moreover, compared with the podocytes from healthy control that usually expressed one class of Ig and one V_HDJ_H pattern, podocytes from patients expressed more classes of Ig, V_HDJ_H patterns and somatic hypermutations. These findings suggested that podocytes can express Igs in normal condition and increase diversity in pathological situations.

NBIGV-DB: A dedicated database of non-B cell derived immunoglobulin variable region

Immunoglobulins (Ig) are important immune molecules that possess highly diverse variable region sequences enabling antigen recognition. According to classical immune theory, B lymphocytes have been considered the only source of Ig production (B-Igs). However, accumulating evidence have suggested that Igs are also produced by many non-B cells (non-B Igs), including epithelial cells, neurons, germ cells, as well as myeloid cells of hemopoietic system. Besides acting as bona fide antibodies, Non-B Igs have alternative cellular functions, such as promotion of cell survival, adhesion and migration. More importantly, Unlike the unlimited sequence diversity of B-Igs, the non-B Igs exhibit conserved V(D)J patterns across the same lineages. To support the analysis and comparison of variable region sequences from Igs, produced by B and non-B cells, we established a database (NBIGV) constituted by a non-B Ig variable region repertoire, which includes 727,989 V_HDJ_H and VκJκ recombination sequences of non-B Igs sequenced from mouse samples. Upon database search, users can view, browse and investigate the variable region sequences of non-B Igs according to respective mice strains and tissues as well as Ig classes. Moreover, users can easily download selected sequences and/or compare sequences of interest with known non-B Ig sequences present in the database using NCBI-BLAST algorithms. Additionally, our database integrates a submission page and supplementary sample information. The NBIGV database may serve as a valuable resource for sequence analyses of Non-B Igs. NBIGV database is freely available at http://nbigv.org.

Single-cell RNA sequencing confirms IgG transcription and limited diversity of VHDJH rearrangements in proximal tubular epithelial cells

Increasing evidence has confirmed that immunoglobulins (Igs) can be expressed in non-B cells. Our previous work demonstrated that mesangial cells and podocytes express IgA and IgG, respectively. The aim of this work was to reveal whether proximal tubular epithelial cells (PTECs) express Igs. High-throughput single-cell RNA sequencing (scRNA-seq) detected Igs in a small number of PTECs, and then we combined nested PCR with Sanger sequencing to detect the transcripts and characterize the repertoires of Igs in PTECs. We sorted PTECs from the normal renal cortex of two patients with renal cancer by FACS and further confirmed their identify by LRP2 gene expression. Only the transcripts of the IgG heavy chain were successfully amplified in 91/111 single PTECs. We cloned and sequenced 469 V_HDJ_H transcripts from 91 single PTECs and found that PTEC-derived IgG exhibited classic V_HDJ_H rearrangements with nucleotide additions at the junctions and somatic hypermutations. Compared with B cell-derived IgG, PTEC-derived IgG displayed less diversity of V_HDJ_H rearrangements, predominant VH1-24/DH2-15/JH4 sequences, biased VH1 usage, centralized VH gene segment location at the 3′ end of the genome and non-Gaussian distribution of the CDR3 length. These results demonstrate that PTECs can express a distinct IgG repertoire that may have implications for their role in the renal tubular epithelial-mesenchymal transition.

Neutralisation of adeno-associated virus transduction by human vitreous humour

Neutralising antibodies (NAbs), caused by past adeno-associated virus (AAV) infection, represent a critical challenge for AAV-mediated gene therapy, with even low NAb titres capable of inhibiting gene transfer, however in protein-rich environments such as the vitreous it is expected that other constituents could also interact with the transduction process. Inhibition of AAV2/2, AAV2/5, AAV2/6 and AAV2/8 transduction by human vitreous humour (VH) obtained from 80 post-mortem eye cups was investigated in this report, with clinically relevant vitreous dilutions as low as 1:2. Unexpectedly, the highest prevalence of inhibition of transduction was observed against AAV2/6, with 66% of tested samples displaying neutralisation at a 1:2 VH dilution. Only two samples showed inhibition of AAV2/8, indicating this serotype is an attractive vector for use in non-vitrectomised eyes of unscreened individuals. Levels of anti-AAV NAbs observed in the VH were much lower than previously observed in serum of a similar Australian population. Among ten tested eye cup pairs, we observed only small variation in anti-AAV NAbs levels between the left and right eye cups. Interaction with 1:2 diluted VH had an augmentation effect on AAV2/8 transduction (p = 0.004), a phenomenon which was not due to albumin or transferrin and which, if developed, might benefit the use of AAV2/8 in clinical settings.

RAG-2 deficiency results in fewer phosphorylated histone H2AX foci, but increased retinal ganglion cell death and altered axonal growth

DNA double-strand breaks (DSBs), selectively visualized as γ-H2AX⁺ foci, occur during the development of the central nervous system, including the retina, although their origin and biological significance are poorly understood. Mutant mice with DSB repair mechanism defects exhibit increased numbers of γ-H2AX⁺ foci, increased cell death during neural development, and alterations in axonogenesis in the embryonic retina. The aim of this study was to identify putative sources of DSBs. One of the identified DSBs sources is LINE-1 retrotransposition. While we did not detect changes in LINE-1 DNA content during the early period of cell death associated with retinal neurogenesis, retinal development was altered in mice lacking RAG-2, a component of the RAG-1,2-complex responsible for initiating somatic recombination in lymphocytes. Although γ-H2AX⁺ foci were less abundant in the rag2^−/− mouse retina, retinal ganglion cell death was increased and axonal growth and navigation were impaired in the RAG-2 deficient mice, a phenotype shared with mutant mice with defective DNA repair mechanisms. These findings demonstrate that RAG-2 is necessary for proper retinal development, and suggest that both DSB generation and repair are genuine processes intrinsic to neural development.

Expression of immunoglobulin A in human mesangial cells and its effects on cell apoptosis and adhesion

IgA nephropathy (IgAN) is characterized by predominant IgA deposition in the glomerular mesangium. It has been considered that the deposited IgA is synthesized by B cells, although recent reports have suggested the implication of other cell types. Therefore, the present study investigated whether glomerular mesangial cells could produce IgA by themselves. Semi‑quantitative reverse transcription-polymerase chain reaction, and immunostaining analysis revealed that the IgA protein and gene transcripts were expressed in primary human renal mesangial cells (HRMCs). Furthermore, the IgA heavy chain (α1 and α2) and the light chain (κ and λ) were localized in the cytoplasm or were located on the cell membranes of human mesangial cells (HMCs). Mass spectrometry results indicated that Ig α1 and Ig α2 were secreted in the culture media of HMCs. The transcripts of Ig α, Ig κ and Ig λ constant regions were detected. The predominant rearrangement pattern of the variable region of Ig κ, was Vκ3‑20*01/Jκ1*01 in HMCs and Vκ1‑12*01/Jκ4*01 in HRMCs. In addition, knockdown of Ig α1 expression by small interfering RNA (siRNA) inhibited cell adhesion and promoted apoptosis. Our findings demonstrate that HMCs can express IgA, and that this expression is associated with cell functions, which may contribute to the deposition of IgA in patients with IgAN.

Impact of Autoantibodies against Glycolytic Enzymes on Pathogenicity of Autoimmune Retinopathy and Other Autoimmune Disorders

Autoantibodies (AAbs) against glycolytic enzymes: aldolase, α-enolase, glyceraldehyde-3-phosphate dehydrogenase, and pyruvate kinase are prevalent in sera of patients with blinding retinal diseases, such as paraneoplastic [cancer-associated retinopathy (CAR)] and non-paraneoplastic autoimmune retinopathies, as well as in many other autoimmune diseases. CAR is a degenerative disease of the retina characterized by sudden vision loss in patients with cancer and serum anti-retinal AAbs. In this review, we discuss the widespread serum presence of anti-glycolytic enzyme AAbs and their significance in autoimmune diseases. There are multiple mechanisms responsible for antibody generation, including the innate anti-microbial response, anti-tumor response, or autoimmune response against released self-antigens from damaged, inflamed tissue. AAbs against enolase, GADPH, and aldolase exist in a single patient in elevated titers, suggesting their participation in pathogenicity. The lack of restriction of AAbs to one disease may be related to an increased expression of glycolytic enzymes in various metabolically active tissues that triggers an autoimmune response and generation of AAbs with the same specificity in several chronic and autoimmune conditions. In CAR, the importance of serum anti-glycolytic enzyme AAbs had been previously dismissed, but the retina may be without pathological consequence until a failure of the blood–retinal barrier function, which would then allow pathogenic AAbs access to their retinal targets, ultimately leading to damaging effects.

Dedifferentiation into blastomere-like cancer stem cells via formation of polyploid giant cancer cells

Our recent perplexing findings that polyploid giant cancer cells (PGCCs) acquired embryonic-like stemness and were capable of tumor initiation raised two important unanswered questions: how do PGCCs acquire such stemness, and to which stage of normal development do PGCCs correspond. Intriguingly, formation of giant cells due to failed mitosis/cytokinesis is common in the blastomere stage of the preimplantation embryo. However, the relationship between PGCCs and giant blastomeres has never been studied. Here, we tracked the fate of single PGCCs following paclitaxel-induced mitotic failure. Morphologically, early spheroids derived from PGCCs were indistinguishable from human embryos at the blastomere, polyploid blastomere, compaction, morula and blastocyst-like stages by light, scanning electron or three-dimensional confocal scanning microscopy. Formation of PGCCs was associated with activation of senescence, while budding of daughter cells was associated with senescence escape. PGCCs showed time- and space-dependent activation of expression of the embryonic stem cell markers OCT4, NANOG, SOX2 and SSEA1 and lacked expression of Xist. PGCCs acquired mesenchymal phenotype and were capable of differentiation into all three germ layers in vitro. The embryonic-like stemness of PGCCs was associated with nuclear accumulation of YAP, a key mediator of the Hippo pathway. Spheroids derived from single PGCCs grew into a wide spectrum of human neoplasms, including germ cell tumors, high-grade and low-grade carcinomas and benign tissues. Daughter cells derived from PGCCs showed attenuated capacity for invasion and increased resistance to paclitaxel. We also observed formation of PGCCs and dedifferentiation in ovarian cancer specimens from patients treated with chemotherapy. Taken together, our findings demonstrate that PGCCs represent somatic equivalents of blastomeres, the most primitive cancer stem cells reported to date. Thus, our studies reveal an evolutionarily conserved archaic embryonic program in somatic cells that can be de-repressed for oncogenesis. Our work offers a new paradigm for cancer origin and disease relapse.

An anti-TNF-α antibody mimetic to treat ocular inflammation

Infliximab is an antibody that neutralizes TNF-α and is used principally by systemic administration to treat many inflammatory disorders. We prepared the antibody mimetic Fab-PEG-Fab (FpF_infliximab) for direct intravitreal injection to assess whether such formulations have biological activity and potential utility for ocular use. FpF_infliximab was designed to address side effects caused by antibody degradation and the presence of the Fc region. Surface plasmon resonance analysis indicated that infliximab and FpF_infliximab maintained binding affinity for both human and murine recombinant TNF-α. No Fc mediated RPE cellular uptake was observed for FpF_infliximab. Both Infliximab and FpF_infliximab suppressed ocular inflammation by reducing the number of CD45+ infiltrate cells in the EAU mice after a single intravitreal injection at the onset of peak disease. These results offer an opportunity to develop and formulate for ocular use, FpF molecules designed for single and potentially multiple targets using bi-specific FpFs.

Effects of intravitreally injected Fc fragment on rat eyes

PURPOSE

Anti-vascular endothelial growth factor (VEGF) drugs are used to treat neovascular eye diseases. Some of these drugs contain Fc fragments (Fc), but it is unknown how their mode of action is influenced by Fc. Therefore, this study investigated the effects of Fc on rat eyes after intravitreal injection.

METHODS

Eighteen Long-Evans rats were intravitreally injected with sterile, biotin-labeled rat Fc (9.1 μg in 5 μl PBS). For control, 5 μl PBS was injected in another nine rats. Animals were sacrificed between 1 and 3 days (group 1), 7 days (group 2), and 14 days (group 3) after injection. The right eyes were examined by electron microscopy (EM). The left eyes were stained by immunohistochemistry to investigate the distribution of Fc and the presence of macrophages.

RESULTS

After 1 day, Fc had penetrated into the anterior chamber and the retina up to the inner nuclear layer, and was located especially in retinal vessels. High numbers of infiltrating cells were present within the vitreous, around the ciliary body, anterior chamber and inside the retina 1-3 days after Fc injection (p < 0.02 group 1 vs. control). Immunohistochemistry and EM showed that they were macrophages or granulocytes in close association with Fc. Ultrastructurally, there were effects on the blood vessels such as thrombocyte activation and fibrin formation.

CONCLUSIONS

Biotin labeling is ideal for investigating the distribution of intravitreally injected proteins in ocular tissue. Fc fragments at a dose corresponding to their concentration in standard AMD treatments induced inflammation, and particularly the attraction of immune-competent cells. This may be associated with the risk of inflammation or endophthalmitis after anti-VEGF treatment, and needs further investigation.

Immunoglobulin G Expression in Human Sperm and Possible Functional Significance

Immunoglobulin G (IgG), the major molecule of the immune system, which was traditionally thought to be produced by differentiated B-lymphocytes, had recently been found in non-immune cells including spermatozoa of rabbit testis. To study if human sperms could produce IgG that might play a role in fertilization, we employed immunofluorescent staining, Western blot, in situ hybridization, RT-PCR (reverse transcription polymerase chain reaction) and immunoelectron microscope and found that human sperms were capable of synthesizing IgG. IgG protein and mRNA were detected in the cytoplasm, mainly the neck region of the sperm and IgG immunoreactivity was found to cover the entire sperm cell. The essential enzymes necessary for IgG synthesis and class switching, RAG1 (recombination activating gene 1), RAG2 (recombination activating gene 2) and AID (activation-induced cytidine deaminase), were also detected in the sperm cells. Furthermore, we found that anti-IgG antibody could inhibit sperm from penetrating Zona-free hamster egg with statistical significance. These discoveries suggested that immunoglobulin G could be produced by human sperms and it might play a role during fertilization.

Aberrant high expression of immunoglobulin G in epithelial stem/progenitor-like cells contributes to tumor initiation and metastasis

High expression of immunoglobulin G (IgG) in many non-B cell malignancies and its non-conventional roles in promoting proliferation and survival of cancer cells have been demonstrated. However, the precise function of non-B IgG remains incompletely understood. Here we define the antigen specificity of RP215, a monoclonal antibody that specifically recognizes the IgG in cancer cells. Using RP215, our study shows that IgG is overexpressed in cancer cells of epithelial lineage, especially cells with cancer stem/progenitor cell-like features. The RP215-recognized IgG is primarily localized on the cell surface, particularly lamellipodia-like structures. Cells with high IgG display higher migration, increased invasiveness and metastasis, and enhanced self-renewal and tumorgenecity ability in vitro and in vivo. Importantly, depletion of IgG in breast cancer leads to reduced adhesion, invasion and self-renewal and increased apoptosis of cancer cells. We conclude that high expression of IgG is a novel biomarker of tumor progression, metastasis and cancer stem cell maintenance and demonstrate the potential therapeutic benefits of RP215-recognized IgG targeted strategy.

Pancreatic Expression of Immunoglobulin G in Human Pancreatic Cancer and Associated Diabetes

OBJECTIVES

The prognosis of pancreatic cancer (PC) is poor and the pathogenesis of PC-associated diabetes is unknown. We investigated the possible expression of immunoglobulin G (IgG) in human pancreatic carcinomas and adjacent pancreatic islets to gain a better understanding of these diseases.

METHODS

We employed immunohistochemistry, Western Blot, real-time polymerase chain reaction, and in situ hybridization to examine IgG expression in PC tissues and adjacent islets with and without cancer-associated diabetes. The IgG mRNA and IgG synthesizing-related enzymes were examined in PC cell lines. The IgG expression and secretion were downregulated with specific small interfering RNA and antibody to IgG followed by flow cytometry to assess its effect on apoptosis of cultured PC cells.

RESULTS

The expression of IgG was detected in pancreatic carcinoma and adjacent islets. Small interfering RNA and antibody treatments induced apoptosis in PC cell lines. In the carcinoma tissue, the levels of IgG expression varied depending on the stages of the cancers with more malignant cancers expressing more IgG (P < 0.05). The IgG levels in cancer cells were also increased when the patients had diabetes or hyperglycemia (P < 0.05). In addition, the extent of IgG expression in the seemingly normal islet cells adjacent to the tumor varied in relation to the grade of cancer differentiation and distance to the cancer nests.

CONCLUSIONS

(1) Immunoglobulin G was locally produced by PC cells and adjacent islet cells. (2) Immunoglobulin G may promote tumor growth by inhibiting cancer cell apoptosis. (3) Locally produced IgG might play a role in PC-associated diabetes.

The PK-Eye: A Novel In Vitro Ocular Flow Model for Use in Preclinical Drug Development

A 2-compartment in vitro eye flow model has been developed to estimate ocular drug clearance by the anterior aqueous outflow pathway. The model is designed to accelerate the development of longer-acting ophthalmic therapeutics. Dye studies show aqueous flow is necessary for a molecule injected into the vitreous cavity to clear from the model. The clearance times of proteins can be estimated by collecting the aqueous outflow, which was first conducted with bevacizumab using phosphate-buffered saline in the vitreous cavity. A simulated vitreous solution was then used and ranibizumab (0.5 mg) displayed a clearance time of 8.1 ± 3.1 days, which is comparable to that observed in humans. The model can estimate drug release from implants or the dissolution of suspensions as a first step in their clearance mechanism, which will be the rate-limiting step for the overall resident time of a candidate dosage form in the vitreous. A suspension of triamcinolone acetonide (Kenalog®) (4.0 mg) displayed clearance times spanning 26-28 days. These results indicate that the model can be used to determine in vitro-in vivo correlations in preclinical studies to develop long-lasting therapeutics to treat blinding diseases at the back of the eye.

IgG expression in trophoblasts derived from placenta and gestational trophoblastic disease and its role in regulating invasion

Immunoglobulin G (IgG) is an important humoral immune factor, which plays a role in innate immunity of the fetus. IgG immunoreactivity was often seen in trophoblasts of placenta. Traditionally, IgG in trophoblasts was believed to be transported from the maternal blood through neonatal Fc receptor (FcRn). Here, we explored the phenomenon of IgG expression and its role in regulating invasion in trophoblasts derived from normal placenta and gestational trophoblastic disease (GTD). IgG expression was detected with an emphasis on mRNA transcripts by using reverse transcription-polymerase chain reaction and hybridization in situ, besides evaluated at the protein level with immunohistochemistry and immunofluorescence. The migration and attachment of normal trophoblast cell line (TEV-1) and choriocarcinoma cell line (JAR) were inhibited with down-regulation of IgG expression. Methotrexate promoted the differentiation of JAR cell line; however, it had little effect on the differentiation of TEV-1 cell line. IgG expression, migration, and attachment of JAR and TEV-1 cell lines were decreased in the presence of methotrexate. Furthermore, statistical analysis showed that the differences in migration and attachment were significant (P < 0.05) for JAR cell line, while no significant difference was found for TEV-1 cell line. Collectively, these results confirmed that with the progression from normal placenta to GTD, the expression of IgG was increased in trophoblasts, which might actively promote the migration and attachment of trophoblasts as an important regulating factor.

Binding of the monoclonal antibody RP215 to immunoglobulin G in metastatic lung adenocarcinomas is correlated with poor prognosis

AIMS

Cancer cell-derived immunoglobulin (Ig)G (cancer-IgG) has been found to be involved in the pathogenesis and progression of many cancers, including lung cancer. The aim of the present study was to investigate the relationship between cancer-IgG expression in lung adenocarcinoma (ADC) and clinicopathological characteristics and clinical outcome.

METHODS AND RESULTS

Immunohistochemical analysis was performed using an RP215 monoclonal antibody to determine cancer-IgG expression in 140 lung ADC patients. Cell migration and invasion were analysed in A549 cell line after short interfering RNA (siRNA) knockdown of IgG and cell sorting by flow cytometry. Our results show that RP215 immunostaining score is correlated significantly with local invasion (P < 0.05) and tumour differentiation (P < 0.05) in ADC. Moreover, RP215 staining was significantly higher in metastatic tumours than in primary tumours (P < 0.0001). The knockdown of IgG resulted in a reduction of cell migration and invasion. In contrast, RP215-positive cells displayed greater migration and invasion ability than RP215-negative cells. Additionally, a higher RP215 immunostaining score was associated significantly with poor prognosis.

CONCLUSIONS

RP215 staining is correlated strongly with differentiation, local invasion, metastasis and clinical outcome of patients with lung ADC. Our results suggest that RP215 can serve as a biomarker for prognosis of lung ADC.

Fab fragment glycosylated IgG may play a central role in placental immune evasion

STUDY QUESTION

How does the placenta protect the fetus from immune rejection by the mother?

SUMMARY ANSWER

The placenta can produce IgG that is glycosylated at one of its Fab arms (asymmetric IgG; aIgG) which can interact with other antibodies and certain leukocytes to affect local immune reactions at the junction between the two genetically distinct entities.

WHAT IS KNOWN ALREADY

The placenta can protect the semi-allogenic fetus from immune rejection by the immune potent mother. aIgG in serum is increased during pregnancy and returns to the normal range after giving birth. aIgG can react to antigens to form immune complexes which do not cause a subsequent immune effector reaction, including fixing complements, inducing cytotoxicity and phagocytosis, and therefore has been called 'blocking antibody'.

STUDY DESIGN, SIZE, DURATION

Eighty-eight human placentas, four trophoblast cell lines (TEV-1, JAR, JEG and BeWo), primary culture of human placental trophoblasts and a gene knock-out mouse model were investigated in this study.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The general approach included the techniques of cell culture, immunohistochemistry, in situ hybridization, immuno-electron microscopy, western blot, quantitative PCR, protein isolation, glycosylation analysis, enzyme digestion, gene sequencing, mass spectrophotometry, laser-guided microdissection, enzyme-linked immunosorbent assay, pulse chase assay, double and multiple staining to analyze protein and DNA and RNA analysis at the cellular and molecular levels.

MAIN RESULTS AND THE ROLE OF CHANCE

Three major discoveries were made: (i) placental trophoblasts and endothelial cells are capable of producing IgG, a significant portion of which is aberrantly glycosylated at one of its Fab arms to form aIgG; (ii) the asymmetrically glycosylated IgG produced by trophoblasts and endothelial cells can react to immunoglobulin molecules of human, rat, mouse, goat and rabbit at the Fc portion; (iii) asymmetrically glycosylated IgG can react to certain leukocytes in the membrane and cytoplasm, while symmetric IgG from the placenta does not have this property.

LIMITATIONS, REASONS FOR CAUTION

Most of the experiments were performed in vitro. The proposed mechanism calls for verification in normal and abnormal pregnancy.

WIDER IMPLICATIONS OF THE FINDINGS

This study identified a number of new phenomena suggesting that aIgG produced by the placenta would be able to react to detrimental antibodies and leukocytes and interfere with their immune reactions against the placenta and the fetus. This opens a new dimension for further studies on pregnancy physiology and immunology. Should the mechanism proposed here be confirmed, it will have a direct impact on our understanding of the physiology and pathology of human reproduction and offer new possibilities for the treatment of many diseases including spontaneous abortion, infertility and pre-eclampsia. It also sheds light on the mechanism of immune evasion in general including that of cancer.

IgG and IgA with potential microbial-binding activity are expressed by normal human skin epidermal cells

The innate immune system of the skin is thought to depend largely on a multi-layered mechanical barrier supplemented by epidermis-derived antimicrobial peptides. To date, there are no reports of antimicrobial antibody secretion by the epidermis. In this study, we report the expression of functional immunoglobulin G (IgG) and immunoglobulin A (IgA), previously thought to be only produced by B cells, in normal human epidermal cells and the human keratinocyte line HaCaT. While B cells express a fully diverse Ig, epidermal cell-expressed IgG or IgA showed one or two conservative V_HDJ_H rearrangements in each individual. These unique VDJ rearrangements in epidermal cells were found neither in the B cell-derived Ig VDJ databases published by others nor in our positive controls. IgG and IgA from epidermal cells of the same individual had different VDJ rearrangement patterns. IgG was found primarily in prickle cells, and IgA was mainly detected in basal cells. Both epidermal cell-derived IgG and IgA showed potential antibody activity by binding pathogens like Staphylococcus aureus, the most common pathogenic skin bacteria, but the microbial-binding profile was different. Our data indicates that normal human epidermal cells spontaneously express IgG and IgA, and we speculate that these Igs participate in skin innate immunity.

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.

Cancer-derived immunoglobulin G promotes tumor cell growth and proliferation through inducing production of reactive oxygen species

Cancer cells have been found to express immunoglobulin G (IgG), but the exact functions and underlying mechanisms of cancer-derived IgG remain elusive. In this study, we first confirmed that downregulation of IgG restrained the growth and proliferation of cancer cells in vitro and in vivo. To elucidate its mechanism, we carried out a co-immunoprecipitation assay in HeLa cells and identified 27 potential IgG-interacting proteins. Among them, receptor of activated protein kinase C 1 (RACK1), ras-related nuclear protein (RAN) and peroxiredoxin 1 (PRDX1) are closely related to cell growth and oxidative stress, which prompted us to investigate the mechanism of action of IgG in the above phenomena. Upon confirmation of the interactions between IgG and the three proteins, further experiments revealed that downregulation of cancer-derived IgG lowered levels of intracellular reactive oxygen species (ROS) by enhancing cellular total antioxidant capacity. In addition, a few ROS scavengers, including catalase (CAT), dimethylsulfoxide (DMSO), n-acetylcysteine (NAC) and superoxide dismutase (SOD), further inhibited the growth of IgG-deficient cancer cells through suppressing mitogen-activated protein kinase/extracellular-regulated kinase (MAPK/ERK) signaling pathway induced by a low level of intracellular ROS, whereas exogenous hydrogen peroxide (H2O2) at low concentration promoted their survival via increasing intracellular ROS levels. Similar results were obtained in an animal model and human tissues. Taken together, our results demonstrate that cancer-derived IgG can enhance the growth and proliferation of cancer cells via inducing the production of ROS at low level. These findings provide new clues for understanding tumor proliferation and designing cancer therapy.

Neuron-derived IgG protects neurons from complement-dependent cytotoxicity

Passive immunity of the nervous system has traditionally been thought to be predominantly due to the blood-brain barrier. This concept must now be revisited based on the existence of neuron-derived IgG. The conventional concept is that IgG is produced solely by mature B lymphocytes, but it has now been found to be synthesized by murine and human neurons. However, the function of this endogenous IgG is poorly understood. In this study, we confirm IgG production by rat cortical neurons at the protein and mRNA levels, with 69.0 ± 5.8% of cortical neurons IgG-positive. Injury to primary-culture neurons was induced by complement leading to increases in IgG production. Blockage of neuron-derived IgG resulted in more neuronal death and early apoptosis in the presence of complement. In addition, FcγRI was found in microglia and astrocytes. Expression of FcγR I in microglia was increased by exposure to neuron-derived IgG. Release of NO from microglia triggered by complement was attenuated by neuron-derived IgG, and this attenuation could be reversed by IgG neutralization. These data demonstrate that neuron-derived IgG is protective of neurons against injury induced by complement and microglial activation. IgG appears to play an important role in maintaining the stability of the nervous system.

Neuron-derived IgG protects dopaminergic neurons from insult by 6-OHDA and activates microglia through the FcγR I and TLR4 pathways

Oxidative and immune attacks from the environment or microglia have been implicated in the loss of dopaminergic neurons of Parkinson's disease. The role of IgG which is an important immunologic molecule in the process of Parkinson's disease has been unclear. Evidence suggests that IgG can be produced by neurons in addition to its traditionally recognized source B lymphocytes, but its function in neurons is poorly understood. In this study, extensive expression of neuron-derived IgG was demonstrated in dopaminergic neurons of human and rat mesencephalon. With an in vitro Parkinson's disease model, we found that neuron-derived IgG can improve the survival and reduce apoptosis of dopaminergic neurons induced by 6-hydroxydopamine toxicity, and also depress the release of NO from microglia triggered by 6-hydroxydopamine. Expression of TNF-α and IL-10 in microglia was elevated to protective levels by neuron-derived IgG at a physiologic level via the FcγR I and TLR4 pathways and microglial activation could be attenuated by IgG blocking. All these data suggested that neuron-derived IgG may exert a self-protective function by activating microglia properly, and IgG may be involved in maintaining immunity homeostasis in the central nervous system and serve as an active factor under pathological conditions such as Parkinson's disease.

SATB1 expression is associated with biologic behavior in colorectal carcinoma in vitro and in vivo

There is increasing evidence that Special AT-rich sequence-binding protein 1 (SATB1) is aberrantly expressed in several cancers and is correlated with clinicopathologic parameters in these tumors. In this study, we showed over-expression of SATB1 in 80 cases of colorectal cancer and in 3 colorectal cancer cell lines and found expression levels were strongly associated with tumor differentiation and stage. Expression levels of SATB1 protein were higher in poorly-differentiated as compared with well-differentiated cell lines, and both quantity and distribution patterns of SATB1 were associated with tumor differentiation and pTNM stage. Strikingly, we further investigated the effect of down regulation of SATB1 expression on malignant phenotypic features in colorectal cancer cells in vitro, and showed that SABT1 down-regulation negatively affected growth potential, anchorage-independent colony formation and cancer cell invasion, and resulted in increased apoptosis. SATB1 expression was positively associated with the expression of various biological and genetic markers, including Cyclin D1, MMP-2, NF-κB, and PCNA, and was associated with loss of APC and BRAF^V600E. These findings suggest that SATB1 is involved in the carcinogenesis, development and progression of colorectal cancer.

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

BACKGROUND

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.

METHODS

IgG expression was assessed by immunohistochemistry, in situ hybridization, immunofluorescence, RT-PCR, and Western blot. The possible significance of IgG was evaluated on tissue array and cell lines. To assess cell viability and proliferation, MTS assay was carried out. Apoptosis was evaluated with propidium iodide and annexin-V staining.

RESULTS

Expressions of IgG and its related genes were detected in cell lines. Abundant gene expressions of Igγ and Igκ chain were detected in PCa tissue samples, but not in normal prostate tissues. In addition, IgG expression was significantly higher in PCa tissues than in the benign prostate hyperplasia tissues (P < 0.001). Igγ expression was positively correlated to Gleason score and histological grade (P < 0.05). Furthermore, in vitro experiments showed that anti-human monoclonal IgG antibody suppressed cell proliferation and increased apoptosis in cultured PCa cells.

CONCLUSION

IgG gene expression in PCa is related to cell differentiation and clinical status. PCa cell produced IgG is involved in the biological behavior of this cancer and may serve as a useful marker for cancer cell differentiation and prognosis. Locally produced IgG could be a potential target for therapy.

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.