Humoral immune system in inflammatory bowel disease: I. Complement levels

A random forest model predicts responses to infliximab in Crohn's disease based on clinical and serological parameters

BACKGROUND

Infliximab (IFX) has revolutionised the treatment for Crohn's disease (CD) recently, while a part of patients show no response to it at the end of the induction period. We developed a random forest-based prediction tool to predict the response to IFX in CD patients.

METHODS

This observational study retrospectively enrolled the patients diagnosed with active CD and received IFX treatment at the Gastroenterology Department in Xiangya Hospital of Central South University between January 2017 and December 2019. The baseline data were recorded in the beginning and were used as predictor variables to construct models to forecast the outcome of the response to IFX.

RESULTS

Our cohort identified a total of 174 patients finally with a response rate of 29.3% (51/174). The area under the receiver operating characteristic curve (AUC) for the model, based on the random forest was 0.90 (95%CI: 0.82-0.98), compared to the logistic regression model with AUC of 0.68 (95%CI: 0.52-0.85). The optimal cut-off value of the random forest model was 0.34 with the specificity of 0.94, the sensitivity of 0.81 and the accuracy of 0.85. We demonstrated a strong association of IFX response with the levels of complement C3 (C3), high density lipoprotein, serum albumin, Controlling Nutritional Status (CONUT) score and visceral fat area/subcutaneous fat area ratio (VSR).

CONCLUSION

A novel random forest model using the clinical and serological parameters of baseline data was established to identify CD patients with baseline inflammation to achieve IFX response. This model could be valuable for physicians, patients and insurers, which allows individualised therapy.

Circadian Clock and Complement Immune System-Complementary Control of Physiology and Pathology?

Mammalian species contain an internal circadian (i.e., 24-h) clock that is synchronized to the day and night cycles. Large epidemiological studies, which are supported by carefully controlled studies in numerous species, support the idea that chronic disruption of our circadian cycles results in a number of health issues, including obesity and diabetes, defective immune response, and cancer. Here we focus specifically on the role of the complement immune system and its relationship to the internal circadian clock system. While still an incompletely understood area, there is evidence that dysregulated proinflammatory cytokines, complement factors, and oxidative stress can be induced by circadian disruption and that these may feed back into the oscillator at the level of circadian gene regulation. Such a feedback cycle may contribute to impaired host immune response against pathogenic insults. The complement immune system including its activated anaphylatoxins, C3a and C5a, not only facilitate innate and adaptive immune response in chemotaxis and phagocytosis, but they can also amplify chronic inflammation in the host organism. Consequent development of autoimmune disorders, and metabolic diseases associated with additional environmental insults that activate complement can in severe cases, lead to accelerated tissue dysfunction, fibrosis, and ultimately organ failure. Because several promising complement-targeted therapeutics to block uncontrolled complement activation and treat autoimmune diseases are in various phases of clinical trials, understanding fully the circadian properties of the complement system, and the reciprocal regulation by these two systems could greatly improve patient treatment in the long term.

Intestinal proteomic analysis of a novel non-human primate model of experimental colitis reveals signatures of mitochondrial and metabolic dysfunction

Animal models recapitulating features of chronic colitis, such as ulcerative colitis, Crohn's disease, or HIV infection, are critical to study disease pathogenesis and test novel therapeutics. In this study, we used a proteomics approach to explore the molecular intestinal response in two rhesus macaque (RM) animal models of experimentally induced colitis using dextran sulfate sodium (DSS) and simian immunodeficiency virus (SIV) infection. Proteomic analysis detected more than 2500 proteins in colonic tissue collected from 30 RMs. Differential protein expression analysis revealed a protein expression pattern in DSS-treated RMs resembling the proteome of human ulcerative colitis. In a group of 12 DSS-treated RMs compared to 6 with no treatment, decrease in expression of proteins related to mitochondrial energy metabolism, including fatty acid metabolism was noted, while innate immune activation pathways, including complement and coagulation proteins were upregulated. SIV infection of RMs resulted in increased innate immune responses related to viral defense. Proteomic signatures of barrier damage were apparent in both DSS treatment or SIV infection. These results demonstrate that DSS treatment in a non-human primate model resembles features of human ulcerative colitis, making this a promising tool to study important immunological mechanisms in inflammatory bowel disease.

Comorbidity of inflammatory bowel disease with atypical hemolytic uremic syndrome in pediatric patients

Atypical hemolytic uremic syndrome (aHUS) is a form of thrombotic microangiopathy mediated by dysregulation of the alternative complement pathway. Complement-amplifying conditions such as respiratory and gastrointestinal infections, pregnancy, malignancy, and systemic autoimmune diseases such as systemic lupus erythematosus have been associated with the clinical manifestation of aHUS. Inflammation of the gastrointestinal tract is a potent stimulus for complement activation, and we describe a series of three pediatric patients with aHUS and comorbidity of inflammatory bowel disease (IBD). In two of the three cases, the diagnosis of aHUS preceded the diagnosis of IBD, perhaps suggesting a mechanistic link between complement dysregulation and thrombotic microangiopathy in the gastrointestinal tract and the ensuing inflammatory changes of IBD.

The intestinal complement system in inflammatory bowel disease: Shaping intestinal barrier function

The complement system is part of innate sensor and effector systems such as the Toll-like receptors (TLRs). It recognizes and quickly systemically and/or locally respond to microbial-associated molecular patterns (MAMPs) with a tailored defense reaction. MAMP recognition by intestinal epithelial cells (IECs) and appropriate immune responses are of major importance for the maintenance of intestinal barrier function. Enterocytes highly express various complement components that are suggested to be pivotal for proper IEC function. Appropriate activation of the intestinal complement system seems to play an important role in the resolution of chronic intestinal inflammation, while over-activation and/or dysregulation may worsen intestinal inflammation. Mice deficient for single complement components suffer from enhanced intestinal inflammation mimicking the phenotype of patients with chronic inflammatory bowel disease (IBD) such as Crohn's disease (CD) or ulcerative colitis (UC). However, the mechanisms leading to complement expression in IECs seem to differ markedly between UC and CD patients. Hence, how IECs, intestinal bacteria and epithelial cell expressed complement components interact in the course of IBD still remains to be mostly elucidated to define potential unique patterns contributing to the distinct subtypes of intestinal inflammation observed in CD and UC.

Regulation of epithelial cell expressed C3 in the intestine - Relevance for the pathophysiology of inflammatory bowel disease?

The complement system not only plays a critical role in efficient detection and clearance of bacteria, but also in intestinal immune homeostasis as mice deficient for key complement components display enhanced intestinal inflammation upon experimental colitis. Because underlying molecular mechanisms for this observation are unclear, we investigated the crosstalk between intestinal epithelial cells (IEC), bacteria and the complement system in the course of chronic colitis. Surprisingly, mouse intestinal epithelial cell lines constitutively express high mRNA levels of complement component 3 (C3), Toll-like receptor 2 (Tlr2) and Tlr4. Stimulation of these cells with lipopolysaccharide (LPS), but not with flagellin, LD-muramyldipeptide or peptidoglycan, triggered increased C3 expression, secretion and activation. Stimulation of the C3aR on these cell lines with C3a resulted in an increase of LPS-triggered pro-inflammatory response. Tissue biopsies from C57BL/6J mice revealed higher expression of C3, Tlr1, Tlr2 and Tlr4 in colonic primary IECs (pIECs) compared to ileal pIECs, while in germ-free mice no differences in C3 protein expression was observed. In DSS-induced chronic colitis mouse models, C3 mRNA expression was upregulated in colonic biopsies and ileal pIECs with elevated C3 protein in the lamina propria, IECs and the mucus. Notably, increased C3b opsonization of mucosa-attached bacteria and decreased fecal full-length C3 protein was observed in DSS-treated compared to untreated mice. Of significant interest, non-inflamed and inflamed colonic biopsy samples from CD but not UC patients displayed exacerbated C3 expression compared to controls. These findings suggest that a novel TLR4-C3 axis could control the intestinal immune response during chronic colitis.

A cross-ethnic survey of CFB and SLC44A4, Indian ulcerative colitis GWAS hits, underscores their potential role in disease susceptibility

The first ever genome-wide association study (GWAS) of ulcerative colitis in genetically distinct north Indian population identified two novel genes namely CFB and SLC44A4. Considering their biological relevance, we investigated allelic/genetic heterogeneity in these genes among ulcerative colitis cohorts of north Indian, Japanese and Dutch origin using high-density ImmunoChip case-control genotype data. Comparative linkage disequilibrium profiling and test of association were performed. Of the 28 CFB SNPs, similar strength of association was observed for rs4151657 (novel ulcerative colitis GWAS SNP) in north Indians (P=1.73 × 10^-10) and Japanese (P=2.02 × 10^-12) but not in the Dutch. Further, a three-marker haplotype was shared between north Indians and Japanese (P<10^-8), but a different five-marker haplotype was associated (P=2.07 × 10^-6) in the Dutch. Of the 22 SLC44A4 SNPs, rs2736428 (novel ulcerative colitis GWAS SNP) was found significantly associated in north Indians (P=4.94 × 10^-10) and Japanese (P=3.37 × 10^-9), but not among the Dutch. These results suggest (i) apparent allelic heterogeneity in CFB and genetic heterogeneity in SLC44A4 across different ethnic groups; (ii) shared ulcerative colitis genetic etiological factors among Asians; and finally (iii) re-exploration of GWAS findings together with high-density genotyping/sequencing and trans-ethnic fine mapping approaches may help identify shared and population-specific risk variants and enable to explain missing disease heritability.

The complement system in inflammatory bowel disease

Complement is well appreciated to be a potent innate immune defense against microbes and is important in the housekeeping act of removal of apoptotic and effete cells. It is also understood that hyperactivation of complement, or the lack of regulators, may underlie chronic inflammatory diseases. A pipeline of products to intervene in complement activation, some already in clinical use, is being studied in various chronic inflammatory diseases. To date, the role of complement in inflammatory bowel disease has not received a lot of research interest. Novel genetically modified laboratory animals and experiments using antagonists to complement effector molecules have kindled important research observations implicating the complement system in inflammatory bowel disease pathogenesis. We review the evidence base for the role and potential therapeutic manipulation of the complement cascade in inflammatory bowel disease.

Mucosal toll-like receptor 3-dependent synthesis of complement factor B and systemic complement activation in inflammatory bowel disease

BACKGROUND

Recent studies link Toll-like receptor 3 (TLR3) to the pathogenesis of inflammatory bowel disease (IBD). Screening TLR3-agonist response in an intestinal epithelial cell line, we found complement factor B mRNA (CFB) potently upregulated and went on to further study localization of complement factor B synthesis and systemic activation of complement in ulcerative colitis and Crohn's disease.

METHODS

In a transcriptome analysis of poly (I:C) stimulated HT-29 cells, we found CFB highly upregulated downstream of TLR3. We sought to confirm CFB upregulation in a microarray gene expression analysis on colonic biopsies from an IBD population (n = 133). Immunohistochemical staining and in situ hybridization were done to identify cellular sources of factor B and CFB. Systemic complement activation was assessed in plasma (n = 18) using neoepitope-based enzyme linked immunosorbent assay.

RESULTS

CFB mRNA and protein were abundantly expressed in the colonic epithelial cell line, and synthesis enhanced by the poly (I:C) TLR3 ligand. In inflamed versus normal colonic mucosa of ulcerative colitis and Crohn's disease, CFB mRNA was the most significantly overexpressed gene and the mRNA abundance ratio was among the 50 highest. Epithelial cells were the dominating site of factor B expression. Systemic complement activation was significantly higher in active than in nonactive IBD.

CONCLUSIONS

This study is the first to link TLR3 to activation of the alternative complement pathway. Complement factor B is potently upregulated locally in IBD in addition to having a possible central role in systemic complement activation. This suggests a prominent role for complement in IBD pathogenesis.

High normal serum levels of C3 and C1 inhibitor, two acute-phase proteins belonging to the complement system, occur more frequently in patients with Crohn's disease than ulcerative colitis

Few data are available on measurements of serum concentrations of complement proteins in inflammatory bowel disease (IBD). Therefore we measured serum levels of C3, C4, and C1-esterase inhibitor (C1-INH) as well as C-reactive protein (CRP) in 167 patients with Crohn's disease (CD) and 111 patients with ulcerative colitis (UC). Median serum concentrations of C3 and C1-INH were significantly higher in CD than in UC. According to multiple logistic regression analysis adjusted to age, sex, activity of disease, and presence of extraintestinal manifestations, IBD patients with high-normal (> or = 128%, > or = 75th percentile ) C1-INH concentrations had significantly (0.0275) higher odds ratio to have a diagnosis of CD than UC. Patients with high-normal C3 (> or = 1.40 g/liter) and high (> or =20 mg/liter) CRP concentrations had an even higher odds ratio of a CD diagnosis (P = 0.0132). Our findings indicate that measurement of C3, C1-INH, and CRP can be used as an additional marker to pANCA/ASCA for distinguishing patients with CD and UC.

Neutrophil recruitment to the gastrointestinal tract

The infiltration of an organ or tissue by neutrophils is the hallmark of acute inflammation. Recent work from many laboratories suggests that neutrophils may play a role in the development of tissue injury in a variety of disease states in the gastrointestinal tract. These diseases include gastritis, necrotizing enterocolitis, ileitis, ulcerative colitis, and ischemia reperfusion injuries. In view of this recent interest in the neutrophil and its relationship to GI diseases, it seems timely to review what is known about neutrophil recruitment to the gastrointestinal tract. This review will therefore focus on the sojourn of the neutrophil from the circulation to its destination in the GI tract.

Surface epithelium related activation of complement differs in Crohn's disease and ulcerative colitis

IgG1 and activated complement are colocalised on the colonic epithelial brush border in active ulcerative colitis. To investigate whether such deposition is specific for ulcerative colitis, we examined ethanol fixed mucosal specimens from 18 patients with Crohn's colitis and 14 with terminal ileitis by indirect two colour immunofluorescence staining. Monoclonal antibodies to the IgG subclasses and to neoepitopes of activated complement C3b and the terminal complement complex were used in combination with rabbit antiserum to C1q, C4c or cytokeratin. Granular deposition of C3b and terminal complement complex were observed at the luminal face of the surface epithelium in 10 of 18 patients with Crohn's colitis. Specimens from eight of 14 patients with ileal involvement were intensely stained for activated complement (primarily C3b) within the surface mucus layer. No epithelial IgG, C1q or C4c deposition was observed. The results suggest that early and late phase complement activation takes place at the luminal face of the epithelium in Crohn's disease. The absence of colocalised IgG and complement components involved in the classical activation pathway (C1q and C4c), however, suggest that other immunopathological mechanisms (the alternative pathway?) are primarily involved in Crohn's disease in contrast with ulcerative colitis.

Review article: assessment of drug therapy in inflammatory bowel disease

This review article surveys the clinical and laboratory parameters used to assess and quantitate inflammation in ulcerative colitis and Crohn's disease, with particular reference to their usage in controlled trials of drugs in inflammatory bowel disease.

Serum bactericidal resistance of faecal Escherichia coli and bactericidal competence of serum from patients with ulcerative colitis

A microtitre method was developed to screen Escherichia coli from 48 patients with ulcerative colitis and 25 controls for serum resistance. Bactericidal resistance was indicated by a change in colour of indicator due to acid production by viable organisms and quantitated by a change in absorbance. The method clearly differentiated between organisms confirmed as resistant or sensitive by conventional techniques. Twenty four (50%) disease and 14 (56%) control E coli specimens showed serum resistance. Bactericidal competence of sera from patients with ulcerative colitis was assessed by incubating sensitive E coli with sera from 10 patients with ulcerative colitis and pooled normal serum. All sera effectively reduced viable counts to less than 6% of original inoculum. This study shows that serum samples from patients with ulcerative colitis are bactericidally competent and that there is no increase in the number of serum resistant E coli in patients with ulcerative colitis.

Dissociation between the functional activity and immunoreactive concentration of C1 esterase inhibitor in active and quiescent Crohn's disease

The plasma immunoreactive concentration and the functional activity of C1 esterase inhibitor (C1INH) were measured in 17 samples from 15 patients with Crohn's disease (CD) and 10 samples from healthy volunteers. C1INH activity was measured by the chromogen substrate method and the immunoreactive concentration by the single radial immunodiffusion method. The functional activity was 95.7 +/- 4.6% in the controls. In CD it was 60.8 +/- 7.5% in the active stage (CDAI greater than 100) and 113.4 +/- 4.9% in the quiescent stage (CDAI less than or equal to 100). There were significant differences between the controls and both the active and quiescent stages (p less than 0.05). The activity was significantly lower in the active than in the quiescent stages (p less than 0.01). However, the difference in the immunoreactive concentration of C1INH in the active and quiescent stages was not significant; it was 27.8 +/- 3.5 mg/dl in the active stage and 33.7 +/- 2.0 mg/dl in the quiescent stage. This difference in the pattern of change between the immunoreactive concentration and the functional activity of C1INH might arise from the mode of C1INH action, with stoichiometric binding to substrates, giving rise to irreversible complexes. These results showed the functional consumption of C1INH in active CD, which may be an aggravating factor in the pathogenesis of the inflammatory process in the patient.

Defective release of C5a related chemo-attractant activity from complement in Crohn's disease

Complement was studied in 20 untreated cases of Crohn's disease and in 20 healthy volunteers by an in vitro activation of the cascade reaction. Total haemolytic complement was normal in all patients. In contrast, activation of the alternative pathway lead to a decreased release of C5a related chemo-attractant activity together with a subnormal utilisation of the main complement component C3. This abnormality of complement function was not related to the activity of the disease, site of involvement or to disease duration. The results suggest that an inadequate stimulation of important neutrophil functions may result when bacterial lipopolysaccharides and other macromolecules activating the alternative pathway penetrate the gut mucosa. A delayed clearance from the tissue of such foreign material could be a further pathogenic factor in Crohn's disease leading to granulomatous inflammation by a foreign body reaction.

Circulating immune complexes in Crohn's disease. Their characterization and interrelationship with components of the complement system

Of the sera from 55 patients with Crohn's disease, 37% showed evidence of anticomplementary activity, C3 and C4 levels were significantly increased in these patients compared with control subjects, although total hemolytic complement levels were normal. C3 inactivation products were demonstrated in 32.9% of serum and plasma samples from 51 patients with CD. This was taken to be evidence of in vivo activation of C3 and the complement system. Activation of the C' system was thought to be caused by circulating immune complexes since evidence of anticomplementary activity could be correlated with incidence of C3 activation. Gel filtration studies carried out on 15 serum samples (13 patients) showing anticomplementary activity showed this activity to be confined to two fractions of molecular weight range greater than 10(6) and 2 x 10(5) - 10(6) daltons. IgG and IgA were present in both these fractions. As the molecular weights of IgG and IgA are lower than the molecular weight range of these fractions, it is possible that the immune complexes were composed of IgG and possibly IgA complexed with antigen.

In vitro studies on cellular and humoral chemotaxis in Crohn's disease using the under agarose gel technique

The locomotor function of polymorphonuclear cells (cellular chemotaxis) and serum chemotactic activity (humoral chemotaxis) were studied in 51 patients with Crohn's disease using a method of migration under agarose gel. To study cellular chemotaxis patient's polymorphonuclear cells were challenged against normal Zymosan activated serum and humoral chemotaxis was evaluated testing the patient's Zymosan activated serum against normal polymorphonuclear cells. Cellular chemotaxis in the Crohn's disease group was normal (although 30% of the 51 patients had migration values out of the normal range), while humoral chemotaxis was significantly lower in Crohn's disease patients than in the control group. However, the value of humoral chemotaxis in the group of Crohn's disease patients treated with steroids was lower than that of patients not treated, thus accounting for the low mean value observed inthe Crohn's disease-group as a whole. The present results suggest that a defective chemotactic response may occur in some Crohn's disease patients, particularly during steroid treatment. These findings might be related either to a defective generation of complement derived chemotactic factors or to the presence of circulating inhibitors.

Complement inhibitors and immunoconglutinins in ulcerative colitis and Crohn's disease

The serum concentrations of the complement inactivators C1INH, C3bINA and beta 1H have been determined in patients with ulcerative colitis and Crohn's disease and their correlation with C3 and properdin factor B examined. The incidence of immunoconglutinins (1K) in these patients was investigated. Raised serum concentrations of C1INH and C3bINA have been found in patients with active disease, but no significant alteration was found in serum concentration of beta 1H. An increasing incidence of positive 1K titres was found with increased length of disease history. These results suggest continuing complement activation in these diseases.

Hyperthyroidism and ulcerative colitis: report of two cases and a review of the literature

Two cases of coexisting ulcerative colitis and hyperthyroidism are discussed. In both patients, thyrotoxicosis preceded the development of the ulcerative colitis. Exacerbations of the thyroid disease led to exacerbations of ulcerative colitis and consequent difficulty in the management of the patients. Although a review of the literature reveals a possible connection with abnormalities of iodine metabolism in the ulcerative colitis patient, no definite conclusions are drawn.

Clq metabolism in ulcerative colitis and Crohn's disease

The metabolism of pure radioiodine labelled Clq has been observed in five patients with ulcerative colitis, five patients with Crohn's disease, and in five control subjects. Both the fractional catabolic rate and the synthesis rate of Clq were increased in the five patients with Crohn's disease and in four of the five patients with ulcerative colitis. The fifth patient was in remission and had a normal synthesis rate. These results support the hypothesis that complement activation plays a role in the pathogenesis of these disease states and that the increased complement activation is primarily via the classical pathway.

[The immune competence of patients with Crohn's disease (author's transl)]

The cell-mediated and humoral immune responses were assessed in 15 patients with Crohn's disease and in 28 age-matched control subjects by means of several in vivo and in vitro methods. The disease activity in most patients was absent or moderate. Studying cellular immunocompetence we investigated the skin reactivity to various recall antigens (Candida, Trichophytin, Mumpsantigen, Streptokinase-Streptodornase, PPD), the primary immune response to Dinitrochlorobenzene (DNCB) and Keyhole Limpet Hemocyanin (KLH), and the lymphocyte transformation induced by mitogens (Phytohemagglutinin, Concanavaline A, Pokeweed Mitogen) and specific antigens. Humoral immunity was studied by measuring immunoglobulins, isohemagglutinins, and the antibody response to KLH. In addition, complement components and (in 10 patients) the proportions of T- and B-lymphocytes in the peripheral blood were evaluated. Cutaneous responsiveness to Candida, Mumps-antigen, SK-SD, and DNCB as well as the cellular immune response to KLH were impaired in patients with Crohn's disease (significance was reached for SK-SD, DNCB, and the mean area of induration). The lymphocyte transformation test with PHA, ConA, and PWM revealed normal results. For specific antigens (PPD, SK-SD, KLH) a good correlation could be demonstrated between delayed hypersensitivity and the in vitro lymphocyte responsiveness. Humoral immunity was not unequivocally impaired in Crohn's disease. Five patients with Crohn's disease proved constantly decreased total absolute lymphocyte counts in peripheral blood. The proportions of T- and B-lymphocytes and the complement-levels were corresponding to those in normal controls. No correlation was found between immunological and clinical parameters. In conclusion, patients with Crohn's disease exhibited a partial impairment of the cellular immune response, whereas humoral immunity was not affected. However, it remains to be elucidated whether this immune defect represents a basic pathogenetic factor in the onset of the disease.

Significance of serum complement levels in patients with gastrointestinal disease

Levels of the serum complement components, C3 and C4, in patients with Crohn's disease, ulcerative colitis, and miscellaneous gastrointestinal disorders were compared with those of normal blood donors. Significant increases of both components were found in all three patient groups, the highest being in patients with Crohn's disease. Generally, levels of C3 and C4 were lower in patients with inactive rather than active Crohn's disease and ulcerative colitis. These results provide some evidence in support of an immunological basis for inflammatory bowel disease. However, in view of the frequent elevation of C3 and C4 in other gastrointestinal diseases, it is equally possible that the complement components are behaving as acute phase proteins.

The humoral immune system in inflammatory bowel disease. II. Immunologlobulin levels

As there have been reports of differences in mean levels of serum immunoglobulins between patients with ulcerative colitis and Crohn's disease, serum IgG, IgA, and IgM were estimated in 158 patients with inflammatory bowel disease and the results correlated with the clinical features of the patients. Although a higher mean IgG level in ulcerative colitis compared to Crohn's disease was confirmed, no difference was found when the comparison was limited to patients with colonic Crohn's disease. Patients with either disease had higher mean IgM levels than controls, and the IgM levels were higher on treatment with corticosteroids and showed a tendency to rise in remission. IgG and IgM levels were also higher in both diseases if extraintestinal manifestations were present. It is concluded that if clinical features, particularly disease site, are taken into account, the overall immunoglobulin responses in these two diseases show no differences.