Antibodies to cathepsin G in Crohn's disease

Neutrophil anti-neutrophil cytoplasmic autoantibody proteins: bactericidal increasing protein, lactoferrin, cathepsin, and elastase as serological markers of inflammatory bowel and other diseases

Inflammatory bowel disease (IBD) is a chronic inflammatory disorder of the gastrointestinal tract comprising Crohn's disease and ulcerative colitis. Although the pathogenesis of the disease is not clearly defined yet, environmental, genetic and other factors contribute to the onset of the disease. Apart from the clinical and histopathological findings, several serological biomarkers are also employed to detect IBD. One of the most thoroughly studied biomarker is anti-neutrophil cytoplasmic autoantibody (ANCA). We herein provide an overview of the current knowledge on the use of ANCA and certain ANCA proteins, such as bactericidal increasing protein, lactoferrin, cathepsin G and elastase, as serological markers for IBD and other diseases.

Serologic markers in inflammatory bowel disease

Inflammatory bowel disease (IBD) is an enduring disease involving mostly young people, with symptoms of bloody diarrhea and abdominal cramps. Several antibodies have been associated with IBD, the 2 most comprehensively studied being autoantibodies to neutrophils (atypical perinuclear anti-neutrophil cytoplasmic antibodies) and anti-Saccharomyces cerevisiae antibodies. This review focuses on the value of these antibodies for diagnosing IBD, differentiating Crohn disease from ulcerative colitis, indeterminate colitis, monitoring disease, defining clinical phenotypes, predicting response to therapy, and as subclinical markers. Pancreatic antibodies and newly identified anti-microbial antibodies (anti-outer membrane porin C, anti-I2, and anti-flagellin) are also reviewed.

Biomarkers in inflammatory bowel disease

PURPOSE OF REVIEW

Inflammatory bowel disease is characterized by chronic intestinal inflammation in the absence of a recognized pathogen. In its classic description, there are two principal forms of inflammatory bowel disease: Crohn disease and ulcerative colitis. The clinical heterogeneity of these disorders alludes to the possibility of diverse pathogenetic mechanisms underlying inflammatory bowel diseases. The purpose of this review is to summarize the latest information on biomarkers of Crohn disease and ulcerative colitis.

RECENT FINDINGS

The authors have focused on serologic markers for which emerging data support their use as predictors of disease evolution. Serologic markers such as perinuclear antineutrophil cytoplasmic antibody, anti-Saccharomyces cerevisiae antibody, anti-OmpC, and anti-I2 may be useful in distinguishing inflammatory bowel diseases from functional disorders and ulcerative colitis from Crohn disease and predicting complications of disease. Genetic markers such as CARD15/NOD2 may be useful in the future when combined with other markers to predict disease course. Biochemical markers of inflammation such as C-reactive protein are useful to stratify patients likely to respond to biologic therapies and to follow response to treatment. In the future, functional genomics and proteomics will be used to rapidly screen patients for subclinical characteristics that can predict disease course and response to therapy.

SUMMARY

A variety of biomarkers can be used to stratify patients with inflammatory bowel disease into more homogeneous subgroups with respect to response to therapy and disease progression.

Antineutrophil cytoplasmic antibodies, anti-Saccharomyces cerevisiae antibodies, and specific IgE to food allergens in children with inflammatory bowel diseases

Differential diagnosis between ulcerative colitis (UC) and Crohn's disease (CD) is difficult in the initial phases in pediatric patients with inflammatory bowel diseases (IBD). This study was performed to determine the significance of anti-neutrophil cytoplasmic antibodies (ANCA) and anti-Saccharomyces cerevisiae antibodies (ASCA) in IBD. ANCA were specified with regard to their antigenic specifity, significance to the diagnosis, and correlation of titer with the disease activity. The occurrence of food allergy was questioned, too. Serum samples from 44 children with UC (n = 23) or CD (n = 21) and from disease-control children (coeliac disease, n = 21) were analyzed for IgG ANCA, ANCA target antigens, IgA and IgG ASCA, and IgE to food allergens. Results show that ANCA occur more frequently in UC than in CD and disease-control (74, 24, and 10%, respectively). The presence of ANCA does not reflect disease activity. Antigenic specificity does not differ in any group. IgA-ASCA are found more often in patients with CD (76% versus 17% in UC). The testing for both ANCA and ASCA enabled clear-cut differential diagnosis between UC and CD based on the high specificity (ANCA+ ASCA- 92.5% for UC, ANCA- ASCA+ 93.2% for CD). Specific IgE to food allergens were found in 8.7, 14.3, and 23.8% of patients with UC, CD, and coeliac disease, respectively. We conclude that combined testing of ANCA and ASCA represents a valuable tool in the differential diagnosis between UC and CD in pediatric patients, minimizing invasive diagnostic procedures. Monitoring of ANCA, its specificity, and titer determination does not bring more information. Testing for specific IgE to food allergens may be considered in individual patients.

Irregular cytokine pattern of CD4+ T lymphocytes in response to Staphylococcus aureus in patients with Wegener's granulomatosis

The initial stage of Wegener's Granulomatosis (WG) is often marked by symptoms of infection and it has been postulated that a bacterial infection could be the aetiologic factor of this disease. The objective of our work was to investigate T-cell-mediated immunity in WG by testing proliferative responses on bacterial antigens and particularly Staphylococcus aureus. We investigated the bulk proliferative response of peripheral blood lymphocytes (PBL) from patients with clinically active WG to gram-positive bacteria and purified proteinase 3 (PR-3), the major target antigen of c-ANCA. We generated S. aureus-specific PBL-derived T-cell lines and T-cell clones (TLC). In two WG patients 27 TLC were characterized in terms of reactivity to bacterial antigens/PR-3, phenotype, HLA class II restriction and pattern of cytokine secretion. Compared to coagulase-negative Staphylococci and beta-haemolytic Streptococci A, reactivity to S. aureus was significantly increased in all patients with WG. Using purified PR-3, we found a PBL proliferation in five out of 25 WG patients. The TLC were S. aureus-specific and did not cross-recognize Streptococci or coagulase-negative Staphylococci. The S. aureus-specific TLC were of the alphabeta-TCR+ CD4+ phenotype and HLA-DR-restricted. These TLC predominantly showed a Th2-type of cytokine secretion. Interestingly, seven of the S. aureus-reactive TLC also recognized the PR-3 antigen. From these data we conclude that Staphylococci-specific HLA-DR-restricted CD4+ T cells may play a key role in the initial triggering of immune responses in WG.

Are anti-neutrophil cytoplasmic antibodies (ANCA) clinically useful in inflammatory bowel disease (IBD)?

Since the first detection of ANCA in IBD, numerous studies have dealt with their prevalence, antigenic specificities, clinical significance, pathophysiological role, and their induction. This review summarizes the information obtained from those studies and shows that ANCA are not directly useful as diagnostic and prognostic factors in IBD. ANCA were detected in 50-85% of patients with ulcerative colitis (UC) and 10-20% of patients with Crohn's disease (CD). Multiple target antigens are recognized by these autoantibodies, including both cytoplasmic and nuclear proteins. A pathophysiological role for ANCA in IBD is far from clear. On the one hand, it is suggested that ANCA are genetic markers of susceptibility for IBD, and on the other hand, the induction of ANCA in those diseases may just be an epiphenomenon of chronic inflammation. We discuss recent evidence that ANCA may be induced by a break-through of tolerance towards bacterial antigens.

Antineutrophil cytoplasmic antibodies in Japanese patients with inflammatory bowel disease: prevalence and recognition of putative antigens

OBJECTIVE

Our aim was to investigate the prevalence of antineutrophil cytoplasmic antibodies (ANCA) in Japanese patients with ulcerative colitis (UC) and Crohn's disease (CD), and the putative antigens recognized by perinuclear staining pattern ANCA (p-ANCA)-positive sera.

METHODS

Sera from UC (n = 52) and CD (n = 43) patients, and from healthy controls (n = 74) were studied. The indirect immunofluorescence (IIF) method was used for the detection of ANCA and its binding pattern. p-ANCA-positive sera were studied further for putative antigens. ELISAs using lactoferrin (Lf), myeloperoxidase (MPO), and cathepsin G (Cat G) as antigens were performed.

RESULTS

ANCA was positive in 40 of the 52 (76.9%) UC (p-ANCA in 33) and in 32 of the 43 (74.4%) CD (p-ANCA in 31) patients. UC and CD patients showed significantly higher titers of p-ANCA than controls; however, no significant difference was observed between UC and CD. In UC, 23, 17, and nine of the 33 patients with p-ANCA-positive sera showed reactivity with Lf, MPO, and Cat-G, respectively. In CD, 21, 20, and 11 of the 31 patients with p-ANCA-positive sera showed reactivity with Lf, MPO, and Cat-G, respectively. Fourteen of the UC and six of the CD patients showed reactivity with two different antigens, and seven of the UC and 11 of the CD patients showed reactivity with all three antigens. The presence of anti-Lf and anti-MPO antibodies was further confirmed by Western blotting.

CONCLUSIONS

ANCA is useful in distinguishing patients with IBD from normal subjects but is not sufficient for the differential diagnosis of CD and UC. p-ANCA reactivity might be derived from the recognition of heterogeneous neutrophil-associated antigens.

Atypical antineutrophil cytoplasmic antibodies with perinuclear fluorescence in chronic inflammatory bowel diseases and hepatobiliary disorders colocalize with nuclear lamina proteins

Antineutrophil cytoplasmic antibodies (ANCA) are frequently associated with chronic inflammatory bowel diseases (IBD) and hepatobiliary disorders. However, their target antigens have not been identified yet. Recently, we observed an atypical perinuclear ANCA fluorescence (p-ANCA) together with an intranuclear staining using ANCA-positive sera from patients with IBD and hepatobiliary disorders. This observation suggests that the target antigens are localized within the nucleus of neutrophilic granulocytes. To further investigate this hypothesis, we examined sera from patients with ulcerative colitis, primary sclerosing cholangitis, autoimmune hepatitis or systemic vasculitis on ethanol or formaldehyde-fixed neutrophils using confocal laser scanning microscopy and immunoelectron microscopy. Counterstaining with propidium iodide, a DNA-specific dye, showed that ANCA-positive sera in IBD and heptobiliary disorders react with intranuclear antigens at the nuclear periphery of the neutrophils. Double immunolabeling techniques revealed that nuclear lamina proteins, lamins A, C and B1, and lamin B receptor were colocalized with the antigen(s) recognized by atypical p-ANCA. No colocalization was observed with classical p-ANCA and antibodies against histones (H1-H4). Our study showed that atypical p-ANCA are antinuclear antibodies reactive with granulocyte-specific antigens present in the nuclear lamina.

Catalase and alpha-enolase: two novel granulocyte autoantigens in inflammatory bowel disease (IBD)

In IBD, the target antigens of anti-neutrophil cytoplasmic autoantibodies (ANCA) have not been fully identified, which limits the analysis of the diagnostic significance as well as of the possible pathophysiological role of these antibodies. In this study, we identify the target antigens of ANCA in large groups of patients with ulcerative colitis (UC) and Crohn's disease (CD). Apart from antibodies against lactoferrin and bactericidal/permeability-increasing protein (BPI), which have been reported before, antibodies against two novel granulocyte antigens were identified: antibodies against a 57/56-kD doublet were found in 38% of samples from UC patients and in 26% of samples from CD patients, whereas antibodies against a 47-kD protein were found in 10% of samples from UC patients and in 18% of samples from CD patients. Partial purification and amino acid sequence analysis identified the 57-kD protein as catalase and the 47-kD protein as alpha-enolase. This study is the first to report catalase and alpha-enolase as granulocyte antigens for autoantibodies in IBD.

Cytotoxic effects of antibodies to proteinase 3 (C-ANCA) on human endothelial cells

Autoantibodies directed against cytoplasmic antigens of neutrophils (ANCA), especially those with specificity for proteinase 3 (PR-3) and myeloperoxidase, are valuable markers for differential diagnosis and monitoring of disease activity in Wegener's granulomatosis (WG) and other vasculitides. Till now, several concepts concerning a direct role of antibodies against PR-3 in the pathogenesis of WG have been discussed. Recently we were able to show that these antibodies recognize PR-3 translocated into the membrane of human endothelial cells. The aim of this study was to investigate putative cytotoxic effects of antibodies to PR-3 on human endothelial cells. Antibodies were obtained by affinity purification of sera from patients with active WG. Purified antibodies to Ro (SS-A), La (SS-B) and RNP served as controls. Purified antibodies to PR-3 displayed a lytic activity against endothelial cells treated with tumour necrosis factor-alpha (TNF-alpha) with the help of cytokine-primed neutrophils as measured in a Cr-release assay. About 100% specific cytotoxicity occurred after 4 h and was independent of complement. Cytotoxic effects were inhibited by coincubation with unprimed neutrophils or preincubation of PR-3 antibodies with purified antigen. Antibodies to Ro (SS-A), La (SS-B) or RNP had no cytotoxic effect. In summary, PR-3 antibody-induced cytotoxicity required (i) expression of PR-3 on the surface of TNF-alpha-treated endothelial cells; and (ii) co-cultivation of cytokine-primed neutrophils. This is to the best of our knowledge the first report on direct cytotoxic effects of PR-3 antibodies on vascular endothelium. Our data give a hint at a PR-3 antibody-mediated mechanism of endothelial injury via antibody-dependent cellular cytotoxicity in WG and other ANCA-related vasculitides.

Anti-neutrophil cytoplasmic antibodies (ANCA) in inflammatory bowel disease: characterization and clinical correlates

ANCA were detected by indirect immunofluorescence in 34 out of 67 patients with ulcerative colitis (UC, 51%) and in 14 out of 35 patients with Crohn's disease (CD, 40%). All but one ANCA-positive sera produced a perinuclear pattern of fluorescence (P-ANCA) on ethanol-fixed neutrophils. On paraformaldehyde-fixed neutrophils 76% of P-ANCA-positive sera in UC and 50% of P-ANCA-positive sera in CD produced cytoplasmic fluorescence, indicating that, indeed, cytoplasmic antigens are recognized by a considerable number of these sera. By Western blot analysis using whole neutrophil extract as a substrate 46% of sera from patients with UC and 32% of sera from patients with CD showed reactivity with either lactoferrin, polypeptides occurring as a doublet of 66/67 kD mol. wt, or polypeptides occurring as a doublet of 63/54 kD mol. wt, respectively. Identical patterns of reactivity have been observed among P-ANCA-positive sera from patients with autoimmune liver disease and rheumatoid arthritis. These data suggest that ANCA of restricted specificities are not specific for inflammatory bowel disease (IBD), but are present in diverse conditions characterized by chronic idiopathic inflammation.

Antibodies to proteinase 3 increase adhesion of neutrophils to human endothelial cells

The detection of anti-neutrophil cytoplasmic antibodies (ANCA), especially those with specificity for proteinase 3, is important in the diagnosis and in monitoring disease activity of Wegener's granulomatosis and related vasculitides. An ubiquitous feature of all ANCA-associated acute vascular injury is lytic necrosis. Adhesion of neutrophils to endothelium is a fundamental early step of the inflammatory response. Recently we were able to show that ANCA recognize their target antigen (proteinase 3) translocated into the membrane of human endothelial cells. The aim of this study was to investigate the effect of ANCA on the adhesion of neutrophils to human endothelial cells. Incubation of endothelial cells with affinity-purified antibodies to proteinase 3 (IgG- and F(ab')2-fractions) led to a marked increase of neutrophil adhesion, with a peak after 4 h and a rapid decrease after 8 h. This effect could be inhibited by preincubation of the endothelial cells with an antibody to endothelial-leucocyte adhesion molecule-1 (ELAM-1). Incubation with antibodies to proteinase 3 also led to an increase of endothelial ELAM-1 expression as measured in a cyto-ELISA and by flow cytometry. Our data demonstrate a direct effect of ANCA on neutrophil-endothelial interactions. The enhanced adhesion of neutrophils occurs time-dependently via induction of ELAM-1 expression on the surface of endothelial cells. Our data give a hint of an ANCA-mediated mechanism of endothelial injury via induction of neutrophil adhesion to vascular endothelium in Wegener's granulomatosis and other ANCA-related vasculitides.

A novel specificity of anticytoplasmic autoantibodies directed against eosinophil peroxidase

Vasculitis associated anticytoplasmic autoantibodies (ANCA) are directed against enzymes in the granules of both neutrophils and monocytes. These autoantibodies can be detected by indirect immunofluorescence technique (IIFT) using ethanol-fixed cytospins. We here report the identification of a novel specificity of autoantibodies, present in the sera of eight patients, that reacted only with eosinophils in the IIFT. By immunoprecipitation and ELISA experiments it was shown that the autoantibodies in these sera were directed against eosinophil peroxidase (EPO). There was no apparent influence on initial substrate conversion rate, but reduced plateau levels suggested increased inactivation of the enzyme in the course of the peroxidase reaction. Flow cytometry studies demonstrated the presence of EPO on the surface of primed eosinophils. Anti-EPO sera and purified anti-EPO immunoglobulins significantly increased the release of reactive oxygen species from primed eosinophils. The patients with anti-EPO antibodies suffered from clinically diverse disorders, with more or less generalized manifestations involving the kidneys, blood vessels, lungs and/or joints.