Decay-accelerating factor (DAF, CD55) in normal colorectal mucosa, adenomas and carcinomas

Association of complement components with risk of colorectal cancer: A systematic review and meta-analysis

BACKGROUND

Complement components could contribute to the tumor microenvironment and the systemic immune response. Nevertheless, their role in colorectal cancer (CRC) remains a contentious subject.

AIM

To elucidate the relationship between complement components and CRC risk and clinical characteristics.

METHODS

Searches were conducted in PubMed, the Cochrane Library, and the China National Knowledge Infrastructure database until June 1, 2023. We included cohort studies encompassing participants aged ≥ 18 years, investigating the association between complement components and CRC. The studies were of moderate quality or above, as determined by the Agency for Healthcare Research and Quality. The meta-analysis employed fixed-effects or random-effects models based on the I² test, utilizing risk ratio (RR) and their corresponding 95% confidence interval (CI) for outcomes. Sensitivity and subgroup analyses were performed to validate the robustness of the collective estimates and identify the source of heterogeneity.

RESULTS

Data from 15 studies, comprising 1631 participants that met the inclusion criteria, were included in the meta-analysis. Our findings indicated that protein levels of cluster of differentiation 46 (CD46) (RR = 3.66, 95%CI: 1.75-7.64, P < 0.001), CD59 (RR = 2.86, 95%CI: 1.36-6.01, P = 0.005), and component 1 (C1) (RR = 5.88, 95%CI: 1.75-19.73, P = 0.004) and serum levels of C3 (standardized mean difference = 1.82, 95%CI: 0.06-3.58, P = 0.040) were significantly elevated in patients with CRC compared to healthy controls. Strong expression of CD55 or CD59 was associated with a higher incidence of lymph node metastasis, whereas strong CD46 expression correlated with a higher incidence of tumor differentiation compared to low CD46 expression (P < 0.05 for all). Although specific pooled results demonstrated notable heterogeneity, subgroup analyses pointed to regional differences as the primary source of inconsistency among the studies.

CONCLUSION

Our analysis underscores that increased levels of specific complement components are associated with a heightened risk of CRC, emphasizing the potential significance of monitoring elevated complement component levels.

Breaking Down Barriers: Epithelial Contributors to Monogenic IBD Pathogenesis

Monogenic causes of inflammatory bowel diseases (IBD) are increasingly being discovered. To date, much attention has been placed in those resulting from inborn errors of immunity. Therapeutic efforts have been largely focused on offering personalized immune modulation or curative bone marrow transplant for patients with IBD and underlying immune disorders. To date, less emphasis has been placed on monogenic causes of IBD that pertain to impairment of the intestinal epithelial barrier. Here, we provide a comprehensive review of monogenic causes of IBD that result in impaired intestinal epithelial barrier that are categorized into 6 important functions: (1) epithelial cell organization, (2) epithelial cell intrinsic functions, (3) epithelial cell apoptosis and necroptosis, (4) complement activation, (5) epithelial cell signaling, and (6) control of RNA degradation products. We illustrate how impairment of any of these categories can result in IBD. This work reviews the current understanding of the genes involved in maintaining the intestinal barrier, the inheritance patterns that result in dysfunction, features of IBD resulting from these disorders, and pertinent translational work in this field.

Complement deficiencies and dysregulation: Pathophysiological consequences, modern analysis, and clinical management

Complement defects are associated with an enhanced risk of a broad spectrum of infectious as well as systemic or local inflammatory and thrombotic disorders. Inherited complement deficiencies have been described for virtually all complement components but can be mimicked by autoantibodies, interfering with the activity of specific complement components, convertases or regulators. While being rare, diseases related to complement deficiencies are often severe with a frequent but not exclusive manifestation during childhood. Whereas defects of early components of the classical pathway significantly increase the risk of autoimmune disorders, lack of components of the terminal pathway as well as of properdin are associated with an enhanced susceptibility to meningococcal infections. The impaired synthesis or function of C1 inhibitor results in the development of hereditary angioedema (HAE). Furthermore, complement dysregulation causes renal disorders such as atypical hemolytic uremic syndrome (aHUS) or C3 glomerulopathy (C3G) but also age-related macular degeneration (AMD). While paroxysmal nocturnal hemoglobinuria (PNH) results from the combined deficiency of the regulatory complement proteins CD55 and CD59, which is caused by somatic mutation of a common membrane anchor, isolated CD55 or CD59 deficiency is associated with the CHAPLE syndrome and polyneuropathy, respectively. Here, we provide an overview on clinical disorders related to complement deficiencies or dysregulation and describe diagnostic strategies required for their comprehensive molecular characterization - a prerequisite for informed decisions on the therapeutic management of these disorders.

Will donor-derived neoplasia be problematic after clinical pig organ or cell xenotransplantation?

There is an increased incidence of certain tumors and other neoplastic disease in organ allotransplant recipients receiving immunosuppressive therapy. Following clinical pig organ xenotransplantation, will there be a risk of the development of neoplasia in the pig graft or in other tissues transplanted with it, eg, lymph nodes? The incidence of neoplasia in young slaughterhouse pigs is very low (<0.005%), but in older pigs is largely unknown (as most pigs are killed within the first six months of life). However, lymphosarcoma, nephroblastoma, and melanoma have been reported in pigs. These tumors should be readily identified by ultrasound or direct inspection and palpation before an organ is excised for clinical xenotransplantation, and so transfer to the human recipient should be unlikely. Post-transplant lymphoproliferative disorder (PTLD) has been reported in pigs receiving intensive immunomodulatory therapy, particularly if this includes whole body irradiation, in an effort to induce mixed hematopoietic chimerism and immunological tolerance. However, the pigs used as sources of organs in xenotransplantation should be free of the porcine lymphotropic herpesvirus that is a key causative factor for PTLD in pigs, and so donor-derived PTLD should not occur. We conclude that the risk of a malignant tumor developing in a transplanted organ from a young pig is small.

Development of a radionuclide-labeled monoclonal anti-CD55 antibody with theranostic potential in pleural metastatic lung cancer

Decay-accelerating factor (CD55 or DAF) inhibits complement-dependent cytotoxicity. We determined that CD55 is overexpressed in 76.47% of human non-small cell lung cancer tissue specimens. We therefore developed a lutetium-177-labeled chimeric monoclonal antibody against CD55. CD55-specific single-chain variable fragment (scFv) was selected from a naïve chicken scFv phage-display library, converted to IgG, and radiolabeled with lutetium-177 to generate a ¹⁷⁷Lu-anti-CD55 antibody. We then charaterized the biodistribution of this antibody in a mouse model of pleural metastatic lung cancer. The ¹⁷⁷Lu-anti-CD55 antibody was primarily retained in tumor tissue rather than normal tissue. Treatment of the mice with ¹⁷⁷Lu-anti-CD55 reduced the growth of lung tumors and improved median survival in vivo by two-fold compared to controls. Finally, ¹⁷⁷Lu-anti-CD55 also enhanced the antitumor activity of cisplatin both in vitro and in vivo. These data suggest ¹⁷⁷Lu-anti-CD55 antibody is a promising theranostic agent for pleural metastatic lung cancer.

Beyond the Role of CD55 as a Complement Component

The complement is a part of the immune system that plays several roles in removing pathogens. Despite the importance of the complement system, the exact role of each component has been overlooked because the complement system was thought to be a nonspecific humoral immune mechanism that worked against pathogens. Decay-accelerating factor (DAF or CD55) is a known inhibitor of the complement system and has recently attracted substantial attention due to its role in various diseases, such as cancer, protein-losing enteropathy, and malaria. Some protein-losing enteropathy cases are caused by CD55 deficiency, which leads to complement hyperactivation, malabsorption, and angiopathic thrombosis. In addition, CD55 has been reported to be an essential host receptor for infection by the malaria parasite. Moreover, CD55 is a ligand of the seven-span transmembrane receptor CD97. Since CD55 is present in various cells, the functional role of CD55 has been expanded by showing that CD55 is associated with a variety of diseases, including cancer, malaria, protein-losing enteropathy, paroxysmal nocturnal hemoglobinuria, and autoimmune diseases. This review summarizes the current understanding of CD55 and the role of CD55 in these diseases. It also provides insight into the development of novel drugs for the diagnosis and treatment of diseases associated with CD55.

Systematic immunohistochemical analysis of the expression of CD46, CD55, and CD59 in colon cancer

CONTEXT

The expression of membrane-bound complement regulatory proteins (mCRPs) that inhibit the complement system in normal tissues is essential for self-protection against an autologous immune reaction. However, the expression patterns of mCRPs, including CD46, CD55, and CD59, are inconsistent in different types of cancer cells.

OBJECTIVES

To determine whether CD46, CD55, and CD59 are differentially expressed in neoplastic and adjacent normal colon tissues and to assess their clinical significance.

DESIGN

Immunohistochemistry was performed on tissue microarrays of cancerous and adjacent normal colon tissues.

RESULTS

The expression levels of CD46, CD55, and CD59 were significantly higher in colon cancer tissues compared with the normal adjacent colon tissues. We found that the expression levels of CD55 and CD59 correlated with the grade of differentiation in colon cancers. In addition, the expression of CD55 and CD59 was greater in stage III and stage IV colon cancers than in stage I and stage II cancers according to staging by the TNM classification.

CONCLUSIONS

CD46, CD55, and CD59 are up-regulated in colon cancer. Specifically, CD55 and CD59 are of clinical relevance to differentiation and TNM staging of colon cancer. These data suggest that CD46, CD55, and CD59 have the potential to be used for molecular staging diagnoses and for colon cancer therapies.

Flow cytometry analysis of coxsackievirus B receptors expression in human CaCo-2 cells

A subset of coxsackieviruses B (CV-B) is able to initiate intestinal infection via the attachment to two cell surface proteins, decayaccelerating factor (DAF) and coxsackie adenovirus receptor (CAR). The aim of the present study was to investigate the expression pattern of these receptors in the polarized CaCo-2 cell line using flow cytometry. The expression of CAR-specific mRNA and proteins was analyzed by reverse transcriptase polymerase chain reaction and western blotting, respectively. Flow cytometry analysis was used to study the surface expression patterns of CAR and DAF. CAR and DAF were well detected at the surface of CaCo-2 cells by flow cytometry. Despite the fact that CAR was susceptible to the action of trypsin, a few amounts of the latter enzyme and a precise dilution did not impair its correct detection by flow cytometry. This technique was used to demonstrate that the density of cells did not influence the expression of CAR at the cell surface. CaCo-2 cells express high levels of CAR and DAF at their surface. Flow cytometry, if used adequately, represents a helpful tool for the study of the interactions between these cells and various viral targets.

CD55 limits sensitivity to complement-dependent cytolysis triggered by heterologous expression of α-gal xenoantigen in colon tumor cells

Engineering cancer cells to express heterologous antigen α-gal and induce the destruction of tumor cells depending on the complement cascade may be a promising strategy of tumor therapy. However, the feasibility and effect of using α-gal to induce colorectal adenocarcinoma cell line cytolysis is not yet known. In this study, we evaluated α-gal expression's ability to sensitize human colorectal adenocarcinoma cell lines to complement attack in cell lines LoVo, SW620, and Ls-174T. Nearly all α-gal-expressing LoVo and SW620 cells were killed by normal human serum (NHS), but α-gal-expressing Ls-174T cells showed no significant lysis. We analyzed the expression levels of membrane-bound complement regulatory proteins (mCRPs) on the three cell lines, and their protective role in α-gal-mediated activation of the complement. LoVo showed no expression of any of the three proteins. CD59 was strongly expressed by SW620 and Ls-174T. CD46 and CD55 varied between the two cell lines. CD46 on SW620 was only half the intensity of CD46 on Ls-174T. Ls-174T showed a notable expression of CD55, while expression of CD55 on SW620 was not detected. The sensitivity of Ls-174T expressing α-gal to NHS greatly increased following the downregulation of CD46 and CD55 with short hairpin RNA (shRNA). However, there is no increase in cell killing when CD59 expression was diminished. Our findings suggest that the use of α-gal as antigen to induce tumor cell killing may be a potential therapeutic strategy in colon cancer and that CD55 plays a primary role in conferring resistance to lysis.

Colonic mucosa-associated diffusely adherent afaC+ Escherichia coli expressing lpfA and pks are increased in inflammatory bowel disease and colon cancer

OBJECTIVE

Colonic mucosa-associated Escherichia coli are increased in Crohn's disease (CD) and colorectal cancer (CRC). They variously haemagglutinate, invade epithelial cell lines, replicate within macrophages, translocate across M (microfold) cells and damage DNA. We investigated genes responsible for these effects and their co-association in colonic mucosal isolates.

DESIGN

A fosmid library yielding 968 clones was prepared in E coli EPI300-T1 using DNA from a haemagglutinating CRC isolate, and resulting haemagglutinating clones were 454-pyrosequenced. PCR screening was performed on 281 colonic E coli isolates from inflammatory bowel disease (IBD) (35 patients), CRC (21) and controls (24; sporadic polyps or irritable bowel syndrome).

RESULTS

454-Pyrosequencing of fosmids from the haemagglutinating clones (n=8) identified the afimbrial adhesin afa-1 operon. Transfection of afa-1 into E coli K-12 predictably conferred diffuse adherence plus invasion of HEp-2 and I-407 epithelial cells, and upregulation of vascular endothelial growth factor. E coli expressing afaC were common in CRC (14/21, p=0.0009) and CD (9/14, p=0.005) but not ulcerative colitis (UC; 8/21) compared with controls (4/24). E coli expressing both afaC and lpfA (relevant to M-cell translocation) were common in CD (8/14, p=0.0019) and CRC (14/21, p=0.0001), but not UC (6/21) compared with controls (2/24). E coli expressing both afaC and pks (genotoxic) were common in CRC (11/21, p=0.0015) and UC (8/21, p=0.022), but not CD (4/14) compared with controls (2/24). All isolates expressed dsbA and htrA relevant to intra-macrophage replication, and 242/281 expressed fimH encoding type-1 fimbrial adhesin.

CONCLUSIONS

IBD and CRC commonly have colonic mucosal E coli that express genes that confer properties relevant to pathogenesis including M-cell translocation, angiogenesis and genotoxicity.

Characterization of novel CD55 isoforms expression in normal and neoplastic tissues

CD55 (decay-accelerating factor, DAF) is overexpressed in several types of cancer, including colorectal cancer. Because of its inhibitory effect on the complement system, it has been suggested as a possible target for cancer immunotherapy. However, CD55 is also expressed in normal tissues, body fluids and stroma, limiting the use of anti-CD55 therapeutic antibodies. Two novel CD55 splice variants or isoforms have recently been identified. These have been shown to contain part or all of intron 7 (CD55(int7+)), in contrast to the previously identified splice variants (CD55(wt)), which do not contain intron 7. Our aim was to determine the pattern of expression of the CD55(int7+) isoforms in normal and cancer tissues and to compare it to CD55(wt). We found that while CD55's isoforms levels vary directly, CD55(wt) is much more abundant (on average 48 times more) than CD55(int7+). Moreover, colon cancers that express high CD55(wt) mRNA levels tend to upregulate CD55(int7+) to a further extent. Finally, we compared the protein levels of CD55(int7+) to CD55(wt) by immunohistochemistry in various colorectal pathological conditions including neoplasia, and found that the levels of both isoforms were elevated in all types of colonic pathology. These results show that the levels of CD55(int7+) in normal tissue are much lower than CD55(wt), while in tumors it is restricted to the epithelial structures unlike CD55(wt). Thus, CD55(int7+) may be a more suitable target for cancer immunotherapy.

Mice overexpressing CD97 in intestinal epithelial cells provide a unique model for mammalian postnatal intestinal cylindrical growth

Postnatal enlargement of the mammalian intestine comprises cylindrical and luminal growth, associated with crypt fission and crypt/villus hyperplasia, respectively, which subsequently predominate before and after weaning. The bipartite adhesion G protein-coupled receptor CD97 shows an expression gradient along the crypt-villus axis in the normal human intestine. We here report that transgenic mice overexpressing CD97 in intestinal epithelial cells develop an upper megaintestine. Intestinal enlargement involves an increase in length and diameter but does not affect microscopic morphology, as typical for cylindrical growth. The megaintestine is acquired after birth and before weaning, independent of the genotype of the mother, excluding altered availability of milk constituents as driving factor. CD97 overexpression does not regulate intestinal growth factors, stem cell markers, and Wnt signaling, which contribute to epithelial differentiation and renewal, nor does it affect suckling-to-weaning transition. Consistent with augmented cylindrical growth, suckling but not adult transgenic mice show enlarged crypts and thus more crypt fissions caused by a transient increase of the crypt transit-amplifying zone. Intestinal enlargement by CD97 requires its seven-span transmembrane/cytoplasmic C-terminal fragment but not the N-terminal fragment binding partner CD55. In summary, ectopic expression of CD97 in intestinal epithelial cells provides a unique model for intestinal cylindrical growth occurring in breast-fed infants.

Cytolytic replication of echoviruses in colon cancer cell lines

BACKGROUND

Colorectal cancer is one of the most common cancers in the world, killing nearly 50% of patients afflicted. Though progress is being made within surgery and other complementary treatments, there is still need for new and more effective treatments. Oncolytic virotherapy, meaning that a cancer is cured by viral infection, is a promising field for finding new and improved treatments. We have investigated the oncolytic potential of several low-pathogenic echoviruses with rare clinical occurrence. Echoviruses are members of the enterovirus genus within the family Picornaviridae.

METHODS

Six colon cancer cell lines (CaCo-2, HT29, LoVo, SW480, SW620 and T84) were infected by the human enterovirus B species echovirus 12, 15, 17, 26 and 29, and cytopathic effects as well as viral replication efficacy were investigated. Infectivity was also tested in spheroids grown from HT29 cells.

RESULTS

Echovirus 12, 17, 26 and 29 replicated efficiently in almost all cell lines and were considered highly cytolytic. The infectivity of these four viruses was further evaluated in artificial tumors (spheroids), where it was found that echovirus 12, 17 and 26 easily infected the spheroids.

CONCLUSIONS

We have found that echovirus 12, 17 and 26 have potential as oncolytic agents against colon cancer, by comparing the cytolytic capacity of five low-pathogenic echoviruses in six colon cancer cell lines and in artificial tumors.

Natural human immunoglobulins in cancer immunotherapy

The natural or innate immunity is the first-line defense against transformed cells. It guarantees the recognition and removal of malignant cells at an early stage and makes manifest cancers an exceptional event. Natural antibodies, which are predominantly IgM molecules, play a major role in these defense mechanisms and they have some typical features in common. They are coded by specific germline families and equipped mainly with lambda-chains, in contrast to the majority of circulating antibodies. The targets that are recognized by these antibodies are not newly synthesized proteins, but instead post-translationally modified carbohydrate structures on membrane-bound glycoproteins and glycolipids. Another typical feature of these natural IgM antibodies is their ability to induce apoptosis in vitro and in vivo in a death domain-independent manner. These results show that natural IgM antibodies represent a huge reservoir of therapeutic antibodies.

Expression of complement restriction factors (CD46, CD55 & CD59) in head and neck squamous cell carcinomas

BACKGROUND

Tumor cells can escape complement-dependent cytotoxicity (CDC) by expressing complement restriction factors (CRFs), CD46, CD55 and CD59. CRF-expression in non-neoplastic mucosa of the head and neck was compared with biopsies of the head and neck squamous cell carcinoma (HNSCC) and cell lines derived from oral squamous cell carcinomas (OSCC).

METHODS

Normal mucosa and HNSCC tumor tissue (poor, moderate, or well differentiated) specimens were immunostained with anti-CRF monoclonal antibodies. Immunostaining of the OSCC cell lines (SCC12 and SCC71) was examined under laser scan fluorescence microscopy.

RESULTS

CD46, CD55 and CD59 were highly expressed in HNSCC cells including T1/T2N0M0 stages. The CRF expression was much lower or absent in non-neoplastic squamous epithelia or in the submucosa of both normal and tumor tissues.

CONCLUSIONS

Enhanced staining of tumor tissues at stages T1/T2 indicates that the CRFs are overexpressed by primary tumors before metastasis to either lymph nodes or organs (N0M0 stage) suggesting that CRFs are formed early during tumorigenesis.

Identification of the decay-accelerating factor CD55 as a peanut agglutinin-binding protein and its alteration in non-small cell lung cancers

PURPOSE

Peanut agglutinin (PNA) recognizes tumor-associated carbohydrates. In this study, we aimed to identify the core protein harboring PNA-binding sugars in the human lung and to explore the relationship with the pathology of primary non-small cell lung cancers (NSCLC).

EXPERIMENTAL DESIGN

PNA lectin blotting was used to detect PNA-binding proteins in the microsomal fraction of lung tissue from 24 patients with NSCLC. The 55- to 65-kDa core peptide PNA-binding protein was characterized by enzymatic treatment and identified by immunoprecipitation and affinity chromatography. The expression level and increase in size of the 55- to 65-kDa PNA-binding protein/decay-accelerating factor (DAF) were compared between normal and tumor regions of the tumor tissue by Western blotting and quantitative PCR.

RESULTS

The 55- to 65-kDa PNA-binding protein was observed in human lung. This was a glycosylphosphatidylinositol-anchored membrane protein carrying O-linked carbohydrates. This core protein was identified as DAF, one of the complementary regulatory proteins. DAF was enlarged to 65 to 75 kDa in NSCLC tumor lesions due to sialylation in the sugar moiety. At the transcription level, DAF levels were significantly lower in tumor regions, suggesting its down-regulation in NSCLC cells.

CONCLUSIONS

DAF was identified as a new PNA-binding protein in the human lung. The down-regulation and heavy sialylation of DAF was associated with pathology in NSCLC, and these alterations make this protein a potential marker for NSCLC.

Cell-surface density of complement restriction factors (CD46, CD55, and CD59): oral squamous cell carcinoma versus other solid tumors

OBJECTIVE

Complement restriction factors (CD46, membrane cofactor; CD55, decay accelerating factor; and CD59, protectin) are overexpressed on tumor cells, and they enable tumor cells to escape from complement-dependent and antibody-mediated killing. Cell-surface density of complement restriction factors (CRFs) on oral squamous cell carcinoma (OSCC) is compared with that found on other solid tumors (breast, pancreas, colon carcinomas, and melanoma) to understand the significance of their diversity.

STUDY DESIGN

The cell-surface expression of CRFs on tumor cells was confirmed with confocal laser scan fluorescent microscopy. Cell suspension enzyme-linked immunosorbent assay (cs-ELISA), which measures the density of cell-surface antigens, was utilized to study CRFs on the cell surface of tumor cells (OSCC, 2 cell lines; breast, 5 cell lines; pancreas, 3 cell lines; colon, 3 cell lines; and melanoma, 9 cell lines).

RESULTS

Confocal laser scan fluorescent microscopy confirmed the expression of CD46, CD55, and CD59 on the cell surface of OSCC cell lines SCC12 and SCC71. The relative densities of cell-surface expression obtained from cs-ELISAs of CRFs on OSCCs are as follows: CD59 > CD55 > CD46. The relative densities of the 3 CRFs in breast and pancreatic carcinomas were similar to those found in OSCCs, whereas the profile of CRFs in melanoma (CD59 > CD55 < CD46) and colon cancer (CD46 > CD55 > CD59) were different.

CONCLUSIONS

These findings indicate diverse strategies adopted by tumor types to resist antibody-mediated complement-dependent cytotoxicity; possibly the factors (exogenous and endogenous) in their respective microenvironments may play a role in the diversity.

Molecular cloning and characterization of novel splicing variants of human decay-accelerating factor

Decay-accelerating factor (DAF) is one of the complement regulatory proteins. Two isoforms of DAF have been identified in humans. In this study, we isolated novel cDNAs encoding five isoforms of DAF from the human lung, which were generated by insertion of new exonic sequences. RT-PCR revealed that all isoforms were expressed in almost all tissues tested, although the expression patterns and levels differed among the tissues. Transfection of isoform vDAF1, 2, and 3 cDNAs into CHO cells showed that these molecules are soluble forms secreted after glycosylation. Isoform vDAF4 and vDAF5 cDNAs included a part of and the entire intron 7 sequence, respectively, and the transfection of vDAF4 cDNA produced a large, glycosylated, membrane-bound form. These results suggest that more than seven isoforms of human DAF are involved in the regulation of complement activation under physiological conditions through their specific structures and localization.

Inhibition of decay-accelerating factor (CD55) attenuates prostate cancer growth and survival in vivo

Decay-accelerating factor (CD55) is a member of membrane-bound complement-regulatory proteins. CD55 expression correlates with poor survival in patients with colorectal cancer and has been implicated in the survival and tumorigenesis of blood-borne malignancies. Histologic analysis of clinical specimens from patients with advanced prostate cancer revealed an increase in CD55 expression in prostate tumor epithelial cells. CD55 was shown to be functionally active and to inhibit complement-mediated lysis in PC-3 and DU145 cells. The percentage of lysis was correlative with the CD55 expression profile observed in these prostate cancer cell lines. These data suggest that CD55 is an important regulator of prostate cancer cell survival. As a result, we have hypothesized that CD55 expression on prostate cancer cells promotes cell survival and contributes to the metastatic potential of prostate cancer cells. To determine the role of CD55 in prostate cancer tumorigenesis and metastasis, we generated PC-3(Luc) prostate cancer cells with CD55 siRNA-targeted disruption. We found that PC-3(Luc)/CD55 siRNA constructs in SCID mice resulted in a significant attenuation of overall tumor burden. Further investigation into the mechanisms of CD55-mediated tumor cell/microenvironment interaction is necessary to understand the role of CD55 in tumor cell survival and metastatic lesion formation.

Complement decay accelerating factor (DAF)/CD55 in cancer

The complement system is a powerful innate mechanism involved in protection of the host against pathogens. It also has a role in the clearance of apoptotic cells and has been implicated in a range of pathologies including autoimmunity and graft rejection. The control of complement is mediated through the complement regulatory proteins (CRPs). These are present on most cells and protect normal cells from complement-mediated attack during innate activation. However, in a range of pathologies and cancer, these molecules are up or down regulated, sometimes secreted and even lost. We will review the expression of CRPs in cancer, focussing on CD55 and highlight other roles of the CRPs and their involvement in leukocyte function. We will also provide some data providing a potential mechanism by which soluble CD55 can inhibit T-cell function and discuss some of the implications of this data.

Decay-accelerating factor (CD55): a versatile acting molecule in human malignancies

The decay-accelerating factor (DAF, CD55) physiologically serves as an inhibitor of the complement system. Moreover, DAF is broadly expressed in malignant tumors. Here, DAF seems to dispose of several different functions reaching far beyond its immunological role, e.g., promotion of tumorigenesis, decrease of complement mediated tumor cell lysis, autocrine loops for cell rescue and evasion of apoptosis, neoangiogenesis, invasiveness, cell motility, and metastasis via oncogenic tyrosine kinase pathway activation, and specific seven-span transmembrane receptors (CD97) binding. Furthermore, DAF has already been included in diagnostic or therapeutic studies. Thereby, studies applying monoclonal anti-DAF antibodies and anti-DAF vaccination for a targeted therapy have been enrolled recently.

HIF-dependent induction of apical CD55 coordinates epithelial clearance of neutrophils

Sites of inflammation are associated with dramatic shifts in tissue metabolism. Inflammation can result in significant tissue hypoxia, with resultant induction of hypoxia-responsive genes. Given this association, we hypothesized that neutrophil (PMN) ligands expressed on epithelial cells may be regulated by hypoxia. Initial studies confirmed earlier results that epithelial hypoxia enhances PMN transepithelial migration and promotes apical clearance of PMN from the epithelial surface. A screen of known PMN ligands revealed a surprisingly stable expression pattern in hypoxia. However, this screen identified one gene, CD55, as a highly hypoxia-inducible molecule expressed on the apical membrane of mucosal epithelia. Subsequent studies verified the induction of CD55 mRNA and protein expression by hypoxia. Overexpression of CD55 by transfection in nonhypoxic epithelia resulted in a similar pattern of apical PMN clearance, and peptide mimetics corresponding to the PMN binding site on DAF blocked such apical clearance of PMN. Studies directed at understanding molecular pathways of hypoxia inducibility revealed that a approximately 200 bp region of the CD55 gene conferred hypoxia inducibility for CD55. These studies identified a functional binding site for the transcriptional regulator hypoxia-inducible factor (HIF). Taken together, these results identify HIF-dependent induction of epithelial CD55 in the resolution of ongoing inflammation through clearance of apical PMN.

Effect of IL-4 on altered expression of complement activation regulators in rat pancreatic cells during severe acute pancreatitis

AIM: To investigate the effect of IL-4 on the altered expression of complement activation regulators in pancreas and pancreatic necrosis during experimental severe acute pancreatitis (SAP).

METHODS: SAP model of rats was established by retrograde injection of 5% sodium taurocholate (1 mL/kg) into the pancreatic duct. We immunohistochemically assayed the expression of three complement activation regulators: decay accelerating factor (DAF; CD55), 20 ku homologous restriction factor (HRF20; CD59) and membrane cofactor protein (MCP; CD46), in the pancreatic acinar cells of rats at 0, 3, 6, 12, and 24 h after the induction of SAP model. Meanwhile the levels of amylase and lipase were determined, and morphological examination was performed. Then, 61 rats were randomly divided into three groups. Group A (n = 21) received no treatment after the SAP model was established; group B (n = 20) was given IL-4 (8 µg/animal) intraperitoneally 0.5 h before the SAP model was established; group C (n = 20) was given IL-4 (8 µg/animal) intraperitoneally 0.5 h after the SAP model was established. Plasma amylase and lipase, extent of pancreatic necrosis and expression of complement activation regulators were investigated 6 h after the induction of SAP model.

RESULTS: Three complement activation regulators were all expressed in pancreatic acinar cells. MCP was not found on the basolateral surface as reported. Contrary to the gradually increasing plasma level of amylase and lipase, expression of complement activation regulators decreased after SAP model was set up. At the same time, the severity of pancreatic necrosis was enhanced. A strong negative correlation was found between the expression of MCP, DAF, CD59 in pancreatic acinar cells and the severity of pancreatic necrosis (r = –0.748, –0.827, –0.723; P<0.01). In the second series of experiments, no matter when the treatment of IL-4 was given (before or after the induction of SAP model), the serum level of amylase or lipase was decreased and the extent of pancreatic necrosis was ameliorated significantly. Compared to SAP control group, the expression of DAF and CD59 in pancreas was reinforced when IL-4 was given before the induction of SAP model (P<0.01, P<0.05), but the expression of MCP was not influenced (P>0.05). The expression of DAF was enhanced, when IL-4 was given after the induction of SAP model (P<0.05), but the expression of CD59 and MCP did not change (P>0.05).

CONCLUSION: Complement activation regulators may participate in the pathogenesis of pancreatic inflammation. Downregulation of complement activation regulators expression may be one of the causes of pancreatic necrosis. IL-4 treatment may control SAP aggravation by enhancing expression of DAF and CD59 in pancreas and decreasing pancreatic necrosis. Moreover, DAF and CD59 may play an important role in the regulation of complement activation regulators during SAP.

Selective expression of a splice variant of decay-accelerating factor in c-erbB-2-positive mammary carcinoma cells showing increased transendothelial invasiveness

By differential-display-PCR a subclone of the SK-BR-3 cell line with high in vitro transendothelial invasiveness was identified to express increased levels of a new alternative splice variant of decay-accelerating factor (DAF). DAF seems to play an important role in some malignant tumours since on the one hand the expression of complement inhibitors on the surface of tumour cells prevents the accumulation of complement factors and in consequence cell lysis. On the other hand, DAF has been identified as a ligand for the CD97 surface receptor which induces cell migration. Immunofluorescence procedures, Western blot analyses, and cDNA clone sequencing were employed to confirm the expression of DAF restricted to invasive tumour cells. Using a radioactive RNA-in situ hybridisation on freshly frozen tissue microarrays and RT-PCR on native tumour tissue, the expression of alternative spliced DAF mRNA was demonstrated in invasive breast cancer. Due to the fact that it could thereby not be detected in normal mammary tissues, it has to be confirmed in larger studies that the DAF splice variant might be a specific tumour marker for invasive breast cancer.

Transfer of functional prostasomal CD59 of metastatic prostatic cancer cell origin protects cells against complement attack

BACKGROUND

Prostasomes are secretory granules produced, stored, and released, by the glandular epithelial cells of the prostate. They express the glycosylphosphatidylinositol (GPI)-anchored complement regulatory protein CD59, which has been shown to be transferred to spermatozoa and erythrocytes.

METHODS

The CD59 content of prostasomes isolated from seminal fluid and malignant prostate cells (PC-3, DU145, and LNCaP) and the transfer of prostasomal CD59 to rabbit erythrocytes (RE) and to PIPLC-treated and unmanipulated cancer cells were investigated using FACS. All prostasomes were also incubated with RE and tested in a hemolytic assay.

RESULTS

Prostasomes from cancer cells had higher expression of CD59 than those of normal cells. Prostasomal CD59 of different origin could be transferred to RE, malignant cell lines stripped of CD59 by PIPLC, or unmanipulated LNCaP cells. Malignant cell prostasomes had an increased ability to inhibit complement-mediated lysis compared to those from non-malignant cells.

CONCLUSIONS

These results point to a novel mechanism by which prostasomes can protect prostatic malignant cells from complement attack.

Complement regulatory proteins in normal human esophagus and esophageal squamous cell carcinoma

BACKGROUND

Altered expression of three complement regulatory proteins, decay-accelerating factor (CD55), membrane cofactor protein (CD46) and homologous restriction factor 20 (CD59) has been identified in human gastrointestinal malignancies, but their expression in esophageal cancer has not been described. Therefore the purpose of the present paper was to study the distribution of these proteins in human normal and malignant esophageal mucosa.

METHODS AND RESULTS

In the normal esophageal mucosa, CD55 predominantly stained on the cell membrane of squamous epithelium in the superficial and prickle cell layers, whereas CD46 most intensely stained on the cell membrane in the basal and parabasal cell layers. In contrast to this reciprocal expression of CD55 and CD46, CD59 was broadly distributed on the cell membrane in all layers. In the esophageal squamous cell carcinoma, CD55 staining was intense in the stroma but was negligible in the cancer cells. In contrast, CD46 and CD59 stained almost uniformly on the tumor cell membrane. There was a significant difference in the intensity of the staining of CD55 and CD46 among cells in various layers of normal esophageal mucosa and esophageal carcinoma cells, but not in the staining of CD59. Similar expression patterns of the three complement regulatory proteins in carcinoma cells and in normal epithelium in the basal and parabasal cell layers were observed.

CONCLUSIONS

These observations on the expression of the three complement regulatory proteins would help understanding of the host immune responses involving the complement system against esophageal squamous cell carcinoma.

Loss of CD55 is associated with aggressive breast tumors

PURPOSE

CD55 is a complement regulatory protein expressed by cells to protect them from bystander attack by complement. CD55 is overexpressed on some tumor cell lines, and in colorectal carcinomas, it has been shown to be an indicator of poor prognostic.

EXPERIMENTAL DESIGN

A large set of samples (480) from patients with primary operable breast cancer followed for 4-192 months were included in the present study. The prognostic significance of CD55 was then investigated in these tumors using an anti-CD55 monoclonal antibody (RM1) that we raised against a synthetic peptide and a standard immunohistochemistry method.

RESULTS

Ninety-five percent of the breast carcinomas expressed CD55 (RM1) with intensity ranging from weak (51%) to strong (6%). High expression of CD55 was significantly associated with low-grade (grades 1 or 2; P = 0.001), lymph node negativity (P = 0.031), and good prognosis tumors (Nottingham Prognostic Index < 3.4; P < 0.001). Survival analysis showed CD55 overexpression was associated with a more favorable outcome and loss of CD55 being associated with poor survival (P = 0.001). Intensity of CD55 expression was significantly correlated (P = 0.002) with intensity of CD59 expression (as shown in a previous study) in these series of patients.

CONCLUSIONS

In conclusion, we found that loss of both CD55 and CD59 in breast carcinomas is associated with a worse prognosis.

Enhanced expression of decay-accelerating factor, a complement-regulatory protein, in the specialized intestinal metaplasia of Barrett's esophagus

Intestinal-type epithelium in Barrett's esophagus, so-called specialized intestinal metaplasia (SIM), is a risk factor for the development of esophageal adenocarcinoma. Surface expression of decay-accelerating factor (DAF), a complement-regulatory protein, is markedly enhanced in intestinal metaplasia of the gastric mucosa. We therefore examined DAF expression in areas of SIM in Barrett's esophagus in an attempt to determine whether DAF is a biomarker of SIM. We obtained 53 endoscopic biopsy specimens from the esophageal columnar mucosae of 45 patients. We immunohistochemically examined the distribution of DAF and 2 other complement-regulatory proteins: homologous restriction factor-20 and membrane cofactor protein. We also examined the expression of DAF messenger RNA in SIM with the use of laser-capture microdissection and reverse transcription-polymerase chain reaction. Of the 53 specimens, 10 were found histologically to involve areas of SIM, 41 were SIM-negative epithelium, and 2 comprised areas of SIM and SIM-negative epithelium. DAF staining was negligible in 35 of 43 specimens of the SIM-negative columnar epithelium, but DAF was strongly stained on the apical surface in all 12 SIM-positive specimens (P <.0001). In the 2 biopsy specimens in which both SIM and SIM-negative columnar epithelium were present, DAF staining was confined to the area of SIM. The expression of DAF messenger RNA was detected significantly more often in SIM than in SIM-negative columnar epithelium (P =.022). We conclude that DAF may be a surface marker for SIM and therefore useful in the identification of areas of the mucosa at risk for the development of adenocarcinoma in Barrett's esophagus.

Inhibition of a complement regulatorin vivo enhances antibody therapy in a model of mammary adenocarcinoma

Membrane-bound complement regulatory proteins provide tumor cells with protection from antibody and complement in vitro. However, complement regulators are widely expressed on normal tissue, and inhibiting the function of complement regulatory proteins on tumor cells in vivo has not been investigated due to the absence of appropriate tumor-targeting strategies. Using a mouse model of rat mammary adenocarcinoma, we demonstrate that tumor-specific targeting of a complement regulator with a blocking antibody has functional consequences with regard to both complement deposition on tumor cells and the efficacy of monoclonal antibody therapy. Rat adenocarcinoma 13762 cells express Crry, a widely expressed rodent regulator of complement activation, and are recognized by C595 MAb, an anti-MUC1 MAb in clinical trials. Anti-rat Crry 5I2 MAb and F(ab)(2) enhanced complement deposition on C595 MAb-sensitized 13762 cells in vitro. In vivo, C595 MAb bound to 13762 tumors, albeit not specifically, but was not therapeutic when administered after tumor challenge. However, the coadministration of 5I2 MAb with C595 MAb resulted in enhanced complement deposition and significantly delayed tumor onset and reduced tumor growth; 5I2 MAb alone also enhanced complement deposition and reduced tumor growth but less effectively than when combined with C595 MAb; 5I2 MAb alone did not directly activate mouse complement, but its inhibitory effect on Crry enhanced complement deposition following complement activation by both the alternative pathway and by natural IgM reactive to 13762 cells present in mouse serum. Our proof of principle study shows that inhibiting the function of a tumor-expressed complement regulatory protein enhances immune-mediated clearance of tumor cells and improves prospects for successful immunotherapy. The results justify further research and development of targeting strategies to inhibit or downregulate complement regulatory proteins on tumor cells.

Advances in the development of a reliable assay for the measurement of stool decay-accelerating factor in the detection of colorectal cancer

We have previously shown that stool concentrations of decay-accelerating factor (DAF; CD55), a membrane-bound complement-regulatory protein, are significantly elevated in patients with colorectal cancer and that the measurement of stool DAF may be a valuable test for the detection of colorectal cancer. Accordingly, we are working to develop a clinically useful immunoassay for fecal DAF. A requirement for such assay is a plentiful and reliable supply of anti-DAF antibodies. We developed a sandwich enzyme-linked immunosorbent assay (ELISA) for DAF in stool specimens, using two monoclonal anti-DAF antibodies recognizing different epitopes on the DAF molecule. When we first used a biotin-labeled antibody and enzyme-linked streptavidin method, we often observed stool interference, probably due to the presence of a substance(s) with biotin activity which non-specifically bound to the Fc portion of IgG of the first anti-DAF antibody on the ELISA wells. By the use of inorganic salts in the sample-dilution buffer and HRP-labeled anti-DAF as second antibody, we circumvented the stool interference and established that the new ELISA system could reliably measure DAF at low concentrations in stool specimens. Because the new assay system uses only monoclonal antibodies, we can now consistently supply ample amounts of antibodies for routine measurement of stool DAF.

Expression of complement regulating factors in gastric cancer cells

AIMS

To investigate the deposition of complement components, C3d and C5b-9, and the expression of complement regulating factors (S protein, membrane cofactor protein (MCP; CD46), protectin (CD59), decay accelerating factor (DAF; CD55), and type 1 complement receptor (CR1; CD35)) in gastric cancers.

METHODS

Specimens of gastric cancer were examined by immunohistochemistry and immunoelectron microscopy.

RESULTS

Four complement regulating factors (S protein, MCP, protectin, and DAF) were expressed on gastric cancer cells, in ultrastructurally localised areas on the cell membrane. CR1 was not expressed. The staining intensity of DAF in both differentiated and undifferentiated adenocarcinomas was significantly higher than in histologically normal gastric epithelium. Furthermore, the staining intensity of DAF in gastric cancers showing a diffusely infiltrating growth pattern was higher than in gastric cancers showing an expanding growth pattern.

CONCLUSIONS

These data indicate that DAF may play a role in cancer cell infiltration and resistance in tumour cells.

Enhanced expression of decay-accelerating factor and CD59/homologous restriction factor 20 in intestinal metaplasia, gastric adenomas and intestinal-type gastric carcinomas but not in diffuse-type carcinomas

AIMS

Variable expression of the complement regulatory proteins, decay-accelerating factor, CD59/homologous restriction factor 20 (HRF20) and membrane cofactor protein has been shown in human gastrointestinal malignancies, but their expression in gastric cancer has not been fully described. Thus, we immunohistochemically defined the distribution of these proteins in human normal gastric mucosa, intestinal metaplasia, adenomas and gastric cancers.

METHODS AND RESULTS

Gastric tissues were obtained by endoscopic biopsy or surgical resection and stained with mouse monoclonal antibodies to decay-accelerating factor, CD59/HRF20, and membrane cofactor protein. In the normal gastric mucosa, membrane cofactor protein was diffusely stained on the basolateral surface of epithelial cells, whereas the expression of decay-accelerating factor and CD59/HRF20 was inconspicuous. In intestinal metaplasia, adenoma and intestinal-type gastric carcinoma cells, decay-accelerating factor and HRF20 were intensely stained on the apical surface; membrane cofactor protein retained its location on the basolateral surface. In diffuse-type gastric carcinomas, the expression of decay-accelerating factor, CD59/HRF20 was lost, but membrane cofactor protein was present on the tumour cell surface.

CONCLUSIONS

These findings suggest that membrane cofactor protein plays a primary role in the regulation of complement activation in normal and neoplastic gastric cells and that the expression pattern of the complement regulatory proteins is closely related to gastric carcinoma development.

The inhibitory effect of CD46, CD55, and CD59 on complement activation after immunotherapeutic treatment of cervical carcinoma cells with monoclonal antibodies or bispecific monoclonal antibodies

The role of membrane-bound complement regulatory proteins (mCRP) in the protection of tumor cells in vivo against elimination by the immune system is still unknown. In this study the effect of expression of these mCRP by cervical cancer cells was investigated. In situ expression of mCRP was observed on cervical carcinomas, normal cervical epithelial cells, and the surrounding stroma. Deposition of C3 and C5b-9 was sporadically found on the tumor cells and the surrounding stroma. A low expression of CD46 was statistically significantly associated with deposition of C3. Comparable expression patterns were shown on primary cervical tumor cell suspensions. A relatively high deposition of C4c was found on these tumor cells, indicating classical pathway activation. Furthermore, it was demonstrated that CD55 and CD59 were the most potent inhibitors of C3 deposition and classical pathway-mediated lysis, respectively, on cervical cancer cell lines. The feasibility of increasing complement activation at the tumor cell membrane surface was demonstrated with an anti-HLA Class I*anti-CD55 bispecific mAb. The potential immunotherapeutic applicability was investigated with both anti-G250*anti-CD55 and anti-Ep-CAM*anti-CD55 bispecific mAbs. An approximate 2-fold increase in C3 deposition, compared with the parental anti-Ep-CAM mAb, was attained with an anti-Ep-CAM*anti-CD55 bispecific mAb when the tumor-associated antigen was expressed in sufficient amounts. These results demonstrate that when tumor-associated antigens are expressed in adequate amounts, bispecific mAbs in vivo may be potent immunotherapeutic agents to enhance an inflammatory reaction at the tumor site.

Enhancement of the complement activating capacity of 17-1A mAb to overcome the effect of membrane-bound complement regulatory proteins on colorectal carcinoma

Adjuvant immunotherapy with 17-1A mAb directed against colorectal carcinoma is found to be effective in patients. However, 52 % of the patients treated with mAb 17-1A showed recurrence within 7 years. This high recurrence rate might be due to inhibition of complement activation by membrane-bound complement regulatory proteins (mCRP). The effect of these complement regulatory proteins might be reduced by blocking mCRP, or be overcome by activating more complement at the tumor cell membrane. In this study the complement-activating capacity of the 17-1A mAb was enlarged by conjugating it to cobra venom factor (CVF) or C3b. The most important C3 regulatory protein, CD55, was blocked using a bispecific mAb directed against the 17-1A / Ep-CAM antigen and CD55. Up to a 13-fold increase in C3 deposition was observed due to 17-1A-CVF and 17-1A-C3b, as compared to 17-1A. CD55 was shown to partly inhibit complement activation by these conjugates. The effect of the bispecific anti-17-1A / Ep-CAM*anti-CD55 mAb was compared with 17-1A conjugates with CVF or C3, and bispecific mAb were shown to be equally or more efficient in complement activation than the 17-1A-CVF or 17-1A-C3b conjugates. Therefore, 17-1A conjugates and anti-17-1A / EpCAM*anti-CD55 bispecific mAb may be promising immunotherapeutic agents for patients with colorectal cancer.

The replication of certain Coxsackie B virus strains in CHO cells

Cell surface molecules that can act as viral receptors may exert an important selective pressure on RNA viral quasi-species. Coxsackie-Adenovirus Receptor and Decay Accelerating Factor (DAF, CD55) have been identified as receptors for Coxsackie B virus. In studies of viral replication using different strains of Coxsackievirus serotype 4 (CBV-4), it was found that despite lack of expression of these cell surface molecules on Chinese Hamster Ovary (CHO) cells and despite their common use as negative controls in Coxsackie B virus receptor assays, two strains were able to replicate, one (V89-4557) without cytopathic effect (CPE), and the other (T318) with strong CPE. A weak signal was obtained using antibodies against enterovirus, visualized with FITC-conjugated antibodies, when the Coxsackievirus B4 strain V89-4557 was inoculated on CHO cells compared to no signal with the non-replicating Coxsackievirus B4 strain VD2921, indicating some degree of binding of the former to the cells.

Regulation of the new coexpressed CD55 (decay-accelerating factor) receptor on stomach carcinoma cells involved in antibody SC-1-induced apoptosis

The human monoclonal antibody SC-1 was isolated from a patient with a diffuse-type adenocarcinoma of the stomach using somatic cell hybridization. The immunoglobulin (Ig)M antibody reacts specifically with diffuse- (70%) and intestinal-type (25%) gastric adenocarcinoma and induces apoptosis in vitro and in vivo. When used in clinical trials with stomach carcinoma patients, significant apoptotic and regressive effects in primary tumors have been observed with the antibody SC-1. The SC-1 receptor is a new 82 kd membrane-bound isoform of glycosylphosphatidylinositol (GPI)-linked CD55 (decay-accelerating factor, DAF). CD55 is known to protect cells from lysis through autologous complement and is coexpressed with the ubiquitously distributed 70 kd isoform. The SC-1-specific CD55 isoform is up-regulated shortly after antibody binding, followed by an internalization of the antibody/receptor-complex, whereas the membranous expression of wild-type CD55 remains unchanged. The apoptotic process is marked by cleavage of cytokeratin 18, indicating the involvement of caspase-6 in the apoptotic process. In contrast to other apoptotic pathways, a cleavage of poly(ADP-ribose)polymerase (PARP) is not observed. The expression of the cell-cycle regulator c-myc becomes up-regulated, whereas expression of topoisomerase IIalpha is down-regulated. Induction of apoptosis leads to an increase in the internal Ca(2+) concentration, which is not necessary for the apoptotic process but for the transport of newly synthesized SC-1-specific CD55 isoform to the membrane.

Polymorphic expression of decay-accelerating factor in human colorectal cancer

BACKGROUND

We have previously shown that expression of decay-accelerating factor (DAF), a complement regulatory protein, is enhanced immunohistochemically on the luminal surface of cancer glands in human colorectal cancer and is detected in stool specimens of patients with colorectal cancer. The amount of DAF present in the stools might be influenced by the stability of DAF on the cell surface which is regulated by biochemical properties such as glycosylation of the protein. In the present study, to help elucidate the mechanism for the release of DAF from human colorectal cancers, we biochemically analyzed DAF expression by western and northern blotting by using surgically resected specimens of colorectal cancers.

METHODS

Surgically resected colorectal cancer tissues were obtained from 10 patients. Expression of DAF was determined by western and northern blotting, and glycosylation of DAF protein was analyzed with glycosidase digestion.

RESULTS

Northern blot analysis demonstrated that the expression of DAF mRNA in colorectal cancer was enhanced two- to threefold compared with normal tissues. In western blotting, expression of DAF protein in the cancer tissue was increased, and heterogeneity in the apparent molecular weight of DAF was observed among patients. When o-linked sugars were removed, this heterogeneity of DAF size diminished.

CONCLUSIONS

The polymorphic expression of DAF in colorectal cancer is likely to reflect variability in the o-glycosylation of the protein. We speculate that this variability could affect the stability of DAF on the surfaces of cancer cells and, in turn, the amount of DAF shed into the stools of colorectal cancer patients.

Expression of complement regulatory proteins-CD 35, CD 46, CD 55, and CD 59-in benign and malignant endometrial tissue

OBJECTIVE

Complement system plays an important role in host defense mechanisms against microorganisms and tumor cells. To protect themselves from autologous complement-mediated damage, normal host tissues express cell membrane-associated complement regulatory proteins (CRPs). To investigate whether neoplastic endometrial tissues overexpress these proteins to escape complement damage, we examined the distribution of complement receptor type 1 (CR1, CD35), membrane cofactor protein (MCP, CD46), decay-accelerating factor (DAF, CD55), and protectin (MACIF, CD59) on frozen endometrial tissue samples.

METHODS

A total of 54 endometrial tissue samples were collected. Cryosections were obtained of 31 benign and 23 malignant tissue specimens. Tissue sections were stained by immunohistochemical staining procedure using specific antibodies and employing the avidin-biotin technique. Quantitation of the protein content of these CRPs was determined using the Samba 4000 image analysis system.

RESULTS

For all four of the CRPs studied, a statistically significant difference in protein expression between the benign and malignant endometrial tissue specimens (P < 0.0001) was observed.

CONCLUSIONS

Overexpression of all the CRPs studied (CD35, CD46, CD55, CD59) was observed in the malignant as compared with the benign endometrial tissues. The upregulation of these CRPs may promote resistance of the endometrial malignant tissue to complement-mediated damage, thereby allowing the tumor cells to escape from cytolysis and thus promoting carcinogenesis.

Decay-accelerating factor in guinea pig stomachs following ischemia reperfusion stress

A complement regulatory protein, decay-accelerating factor (DAF, CD55), is known to protect host tissues from autologous complement activation. DAF is present on the apical side of human gastric epithelial cells, and its expression increases during gastritis. To develop an animal model for analysis of DAF expression on gastric cells, a mAb to guinea pig DAF was successfully used. Although DAF expression in the mucosal epithelium of the stomach is weak, as judged by immunohistochemical staining with the mAb, it was temporarily up-regulated at 12 and 24 h, and at 3 days after ischemia reperfusion (I/R) (p < 0.05). The DAF mRNA level in gastric tissues was determined by Northern blot analysis and found to be highest at 6 h after I/R, returning to the baseline at 24 h. Strong DAF mRNA expression was observed in the cytoplasm of cells beneath the eroded tissues 6 h after I/R. In guinea pigs, alternative splicing of DAF mRNA generates both GPI-anchored types and transmembrane types of DAF. RT-PCR analysis revealed that mRNAs of the transmembrane types had become significantly dominant by 6 h after I/R, whereas levels for the GPI-anchored types remained unchanged. In guinea pigs depleted of complement by cobra venom factor treatment, the area of erosion and the up-regulation of DAF expression in gastric epithelial cells after I/R were significantly limited compared with the normocomplementemic group, indicating that DAF may be up-regulated by an inflammatory stress.

Immune evasion of tumor cells using membrane-bound complement regulatory proteins

Membrane-bound complement regulatory proteins (mCRPs) play an important role in the protection of cells from complement-mediated injury. It is now apparent that malignant tumor cells also express these proteins to escape complement attack. Here, Arko Gorter and Seppo Meri discuss the implications of complement resistance for the immunotherapeutic treatment of solid tumors with monoclonal antibodies.

Structural characterization of mouse CD97 and study of its specific interaction with the murine decay-accelerating factor (DAF, CD55)

CD97 is a newly identified, activation-associated human leucocyte antigen with seven putative transmembrane domains. It has an extended extracellular segment containing several adhesion molecule structure motifs, and has been shown to interact with the human complement regulator, decay-accelerating factor (DAF, CD55). To understand further the interaction between CD97 and DAF, as well as the structure and function of CD97 in general, we have cloned the mouse CD97 cDNA and studied the encoded protein for its membrane association property and ability to interact specifically with the murine decay-accelerating factor. The full-length mouse CD97 cDNA that we have cloned and characterized encodes a protein that is 60% identical to the three epidermal growth factor (EGF) domain-containing form of human CD97 but does not contain the Arg-Gly-Asp (RGD) motif which is present in human CD97. Two other alternatively spliced forms of mouse CD97 were also identified. These forms differ by the number of EGF-like sequence repeats present in the N-terminal region. Northern blot analysis revealed that CD97 is expressed widely in mouse tissues and in resting as well as activated cultured mouse splenocytes. Transient transfection of human embryonic kidney (HEK) 293 cells with the mouse CD97 cDNA in a green-fluorescence protein vector (pEGFP-N1) showed plasma membrane targeting of the expressed protein. Western blot analysis confirmed its membrane association and identified the existence of a processed C-terminal fragment, supporting the notion that CD97 on the cell membrane is composed of post-translationally generated subunits. Adhesion studies demonstrated that normal, but not DAF knockout mouse erythrocytes and splenocytes adhered to mouse CD97-transfected HEK cells. The interaction of CD97 and DAF was found to be species-restrictive in that human erythrocytes were unable to bind to mouse CD97-transfected HEK cells. These results indicate that the general structure, membrane association property and DAF-binding ability of CD97 are conserved and that the adhesive interaction between CD97 and DAF is independent of the RGD motif. The finding that CD97 is distributed widely among various mouse tissues suggests that CD97 may have other roles beyond lymphocyte activation.

Expression and regulation by interferon-gamma of the membrane-bound complement regulators CD46 (MCP), CD55 (DAF) and CD59 in gastrointestinal tumours

The membrane-bound complement inhibitors CD46 (membrane cofactor protein), CD55 (decay-accelerating factor) and CD59 (protectin) protect tumour cells against lysis by activated complement. In this study, a total of 14 (3 gastric, 3 colonic and 8 pancreatic) gastrointestinal tumour cell lines were examined for the expression of CD46, CD55 and CD59 with respect to the regulatory efficacy of interferon-gamma (IFN-gamma). The effects of IFN-gamma on mRNA and protein expression levels of CD46, CD55 and CD59 were evaluated by Northern blot hybridisation, RT-PCR, flow cytometry and immunostaining. In unstimulated cell lines, CD46 and CD59 transcripts were expressed at comparable levels, whereas the basal expression of CD55 mRNA was heterogeneous. The complement inhibitor proteins were detected in all cell lines using specific antibodies. Additional immunohistochemical stainings of gastrointestinal tissue specimens supported these findings. IFN-gamma evoked a weak induction of certain transcripts in a subset of the cell lines. Upregulation of protein expression was only observed in HT29 cells for CD55 and CD59 and was accompanied by a marked increase of the corresponding transcripts. We conclude that membrane-bound complement inhibitors are broadly expressed in gastrointestinal tumour cells and vary in their susceptibility to IFN-gamma. Thus, they may be involved in tumour escape mechanisms in gastric, pancreatic and colorectal cancer.

Altered expression of membrane inhibitors of complement in human gastric epithelium during Helicobacter-associated gastritis

AIMS

Membrane inhibitors of complement are thought to protect bystander cells from complement mediated damage. Expression of these proteins is enhanced in the colonic mucosa of patients with ulcerative colitis. Our aim was to investigate the regulation of complement activity in Helicobacter-associated chronic gastritis.

METHODS AND RESULTS

We immunohistochemically assayed expression of three membrane inhibitors of complement, decay accelerating factor (DAF; CD55), 20 kDa homologous restriction factor (HRF20; CD59) and membrane cofactor protein (MCP; CD46), in 55 biopsy specimens of the human gastric mucosa. DAF, expressed in 33 (60%) of biopsy specimens, and HRF20, expressed in 45 (82%) of the samples, were located mainly on the apical surface of the epithelial cells, whereas MCP, expressed in 48 (87%) of the biopsies, was found on the basolateral surface. We found strong correlation between expression of DAF on gastric mucosal epithelium and the severity of mucosal infiltration of neutrophils (rs = 0.875, P < 0.0001) and mononuclear cells (rs = 0.773, P < 0.0001). No significant correlation was observed between HRF20 expression and neutrophil or mononuclear cell infiltration, while there was a weak negative correlation between MCP expression and these cellular infiltrations. When we assayed immunostaining of Helicobacter pylori (H. pylori) in these biopsy specimens, strong correlation with the degree of neutrophil (P < 0.0001) and mononuclear cell (P < 0.0001) infiltration were observed. The expression of DAF and H. pylori infection in these biopsies were also significantly (P < 0.0001) correlated. No correlation between HRF20 expression and H. pylori infection was observed, but we did find a significant negative correlation (P < 0.005) between the expression of MCP and H. pylori infection.

CONCLUSIONS

Our results, demonstrating altered expression of membrane inhibitors of complement in gastric mucosa during inflammation and/or H. pylori infection, suggest that complement may significantly participate in the pathology of gastric inflammation. Moreover, DAF and MCP may play an important role in the regulation of complement activation in the alimentary tract.

Expression of cell membrane complement regulatory glycoproteins along the normal and diseased human gastrointestinal tract

BACKGROUND/AIMS

Uncontrolled complement activation may be of immunopathological importance in inflammatory diseases of the gastrointestinal tract. Expression of membrane bound factors that regulate complement activation was therefore studied in situ.

METHODS

Frozen tissue specimens were obtained from patients with Helicobacter pylori gastritis, coeliac disease, Crohn's disease, or ulcerative colitis, and from histologically normal controls. Sections were examined by immunofluorescence with monoclonal antibodies to protectin (CD59), decay accelerating factor (DAF), and membrane cofactor protein (MCP).

RESULTS

Protectin and MCP were widely expressed in normal and diseased mucosae. MCP was generally observed basolaterally on all epithelial cells, whereas apical protectin expression was more intense on the epithelium of normal colonic mucosa than in the normal duodenum (p = 0.001). Epithelial DAF and to some extent protectin were upregulated in gastritis, coeliac disease, and inflammatory bowel disease. Areas of the stomach with intestinal metaplasia expressed DAF, unlike the adjacent gastric epithelium. Parietal cells of the gastric body expressed neither protectin nor DAF.

CONCLUSION

Epithelial complement inhibitory molecules were expressed differently at various normal gastrointestinal sites and also in association with mucosal disease, suggesting variable protective potential. Such molecules could play a role in the development of gastric atrophy by protecting areas of intestinal metaplasia. Conversely, parietal cells appeared to be potentially vulnerable targets for complement attack.