Hypercatabolism of complement in Crohn's disease--assessment of circulating C3c

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.

Polymorphism of complement C3 in chronic inflammatory bowel disease. Predominance of the C3F gene in Crohn's disease

Polymorphism of the third component of complement (C3), occupying a key position in cascade reactions, was investigated in 125 consecutive outpatients, 53 with Crohn's disease and 72 with ulcerative colitis. A sample of 1378 randomly selected healthy volunteers of Danish origin served as controls. Occurrence of the F and FS phenotype of C3 (C3F and C3FS ) was increased in the group of Crohn's disease patients (chi 2 = 2.80, p less than 0.05, one-tailed test) and in a subgroup of Crohn patients with the gastrointestinal disease process confined to ileum (chi 2 = 6.91, p less than 0.01). C3 phenotype distribution was unaffected in ulcerative colitis. Only S and F alleles of C3 ( C3S and C3F) were recognized and C3F frequencies were 0.33 in Crohn patients with small bowel disease, 0.23 in all Crohn patients, 0.18 in ulcerative colitis patients and 0.17 in healthy volunteers. The results are compatible with a positive association of the C3F gene and Crohn's disease located in the small bowel.

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.

Inflammatory bowel disease. Part I: Nature and pathogenesis

Once regarded as medical curiosities, ulcerative colitis and Crohn's disease have achieved a remarkable change in status recently and today are among the more compelling of all human illnesses. The cause(s) of inflammatory bowel disease (IBD) are not known. Genetic, environmental, microbial, and immunologic factors are involved, but the precise mechanisms are obscure. The incidence of ulcerative colitis is relatively stable, while Crohn's disease continues to increase in frequency. In 10% to 15% of patients, it is hard to differentiate between ulcerative colitis and Crohn's colitis; however, problems with diagnosis usually resolve with time and repeated examinations. In part I of his two-part monograph on IBD, Dr. Kirsner addresses the nature and pathogenesis of the disease. Increased study of ulcerative colitis and Crohn's disease in recent years has generated new knowledge regarding their etiology. Part I focuses on microbial, immunologic, and genetic mechanisms and the inflammatory processes involved in the disease. In part II, which will be presented in next month's issue of Disease-a-Month, Dr. Kirsner deals with the clinical features, course, and management of IBD, based on the author's 55 years of experience with these problems and supplemented by critical examination of the recent (1988-1990) literature. Particular attention is directed to the symptoms and physical findings of ulcerative colitis and Crohn's disease, the laboratory, radiologic, endoscopic, and pathologic features, and the many systemic complications. The IBDs are mimicked by several enterocolonic infections and other conditions, making differential diagnosis necessary. Inflammatory bowel disease in children and the elderly conforms to conventional clinical patterns modified by the health circumstances of the respective age groups. Because the cause of IBD has not been established, current medical therapy is facilitative and supportive rather than curative. The principles of medical treatment are approximately the same for ulcerative colitis and Crohn's disease. Treatment emphasizes a program rather than a drug and also considers the individuality of the therapeutic response. A clearer understanding of dietary and nutritional needs, including hyperalimentation and electrolyte and fluid balance, aids treatment. Antidiarrheal and antispasmodic preparations and sedatives are prescribed for symptom relief. The bowel inflammation is controlled with sulfasalazine or the newer 5-amino salicylic acid (5-ASA) compounds, antibacterial drugs for complications of Crohn's disease and IBD, adrenocortical steroids, and the immunosuppressive compounds 6-mercaptopurine (6-MP), azathioprine, and cyclosporine, as determined in each patient. The surgical procedures available for treatment of ulcerative colitis include total proctocolectomy and ileostomy or ileoanal anastomosis.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Serum interferon activity in inflammatory bowel disease. Arachidonic acid release and lipoxygenation activated by alpha-class interferon in human neutrophils

Serum interferon (IFN) of alpha-class was studied in 64 consecutive patients, 26 with Crohn's disease, 38 with ulcerative colitis, and in 34 healthy volunteers. Detectable IFN-alpha in 10 patients was associated with a moderate to severe activity of chronic inflammatory bowel disease (CIBD). However, 19 of 28 patients (68%) with activity in their disease did not have elevated IFN-alpha levels. The three groups, ulcerative colitis, Crohn's disease, and healthy volunteers did not reveal any statistically significant difference in serum IFN-alpha, as four of 34 healthy controls without intercurrent infections had elevated levels as well. Possible effects of alpha, beta, and gamma classes of IFN on endogenous arachidonic acid (AA) release and metabolism in human neutrophils was investigated in a substudy. IFN-alpha caused a dose-dependent release of AA from phospholipids and metabolism of a modest fraction of leukotriene B4 (LTB4) and 5-hydroxyeicosatetraenoic acid (5-HETE) at doses reaching a maximum of 100 IU/ml. IFN of the beta and gamma classes did not exert such effects. Addition of complement 5a to cells activated by IFN-alpha caused induction of increased 5-lipoxygenase activity with unchanged release of AA. As only 16% of all CIBD patients had elevated IFN-alpha levels as compared to 12% among the group of healthy volunteers, IFN-alpha does not seem to be of importance for the perpetuation of the inflammatory reaction in ulcerative colitis or Crohn's disease, and other factors may therefore be responsible for activation of the inflammatory cells to production of LTB4 and 5-HETE.

Activation of neutrophil chemotaxis by leukotriene B4 and 5-hydroxyeicosatetraenoic acid in chronic inflammatory bowel disease

Circulating neutrophils were investigated in 15 patients with Crohn's disease (CD), 15 with ulcerative colitis (UC), and 15 healthy volunteers. Dose-response curves for chemotaxis in Boyden chambers were analysed for sensitivity to leukotriene B4 (LTB4), its 20-hydroxy-LTB4 (20-OH-LTB4) and 20-carboxy-LTB4 (20-COOH-LTB4) catabolites, and 5- and 15-hydroxyeicosatetraenoic acids (HETEs). Positive controls included: complement 5a (C5a), formy-L-methionyl-L-leucyl-L-phenylalanine (f-Met-Leu-Phe), and casein. Control chemotaxis test were performed at concentrations yielding optimal responses in leucocytes of healthy volunteers. Chemotaxis to suboptimal concentrations of LTB4 1.0 and 3.2 nmol/l, and 5-HETE 316 nmol/l, was markedly depressed in patients with chronic inflammatory bowel disease (CIBD). Analyses of individual dose-response curves revealed an underlying decreased sensitivity to LTB4 in 11 out of 30 patients, to 5-HETE in 10 out of 30 patients with a corresponding decrease of median sensitivity to LTB4 and 5-HETE in both CD and UC. Peak responses to LTB4, 5-HETE, f-Met-Leu-Phe, and casein were identical in the three groups tested, whereas the C5a values were significantly depressed in both groups of patients (p less than 0.05). The potency of LTB4 exceeded that of 5-HETE by a factor of approximately 100 whereas 20-OH-LTB4 was nearly as potent as LTB4. 20-COOH-LTB4 and 15-HETE did not activate chemotaxis of human neutrophils. These findings are suggestive of a competitive inhibition of receptors with heterogeneity for LTB4 and 5-HETE.(ABSTRACT TRUNCATED AT 250 WORDS)

Defective modulation of complement in Crohn's disease. C3b opsonization of zymosan by the alternative pathway

Opsonization of zymosan by plasma complement was studied in 12 consecutive patients with untreated, well-established Crohn's disease and in 12 healthy volunteers. Binding of C3b to zymosan was markedly increased in patients with Crohn's disease during the first 30 min of the alternative pathway reaction, whereas consumption of the native C3 protein was within the normal range in all patients. Our results are consistent with a decreased capacity for degradation of activated C3,C3b by the I-H factor inactivator system. This immunologic abnormality may contribute to a chronic activation of the complement sequence, previously demonstrated in Crohn's disease, and to a release of split products of inflammation-promoting character.

Subnormal sensitivity of neutrophils to complement split product C5a in rheumatoid arthritis: relation to complement catabolism and disease extent

The capacity of circulating neutrophils for activation by complement was studied in outpatients with classical or definite rheumatoid arthritis during treatment with dextropropoxyphene only. Analysis of dose-response in the Boyden chamber assay of chemotaxis showed that sensitivity to the potent, complement derived anaphylatoxin, C5a, was markedly decreased, especially in those patients with few joints involved. In contrast, peak response to C5a was within the normal range. Increased complement 3c split products in plasma of the patients suggested involvement of complement cascade reactions. Subnormal sensitivity of neutrophils to phlogistic mediators released by complement may tend to limit their recruitment and potentially tissue destroying secretion locally in rheumatoid arthritis.

Subnormal activation of phagocytes by complement in chronic inflammatory bowel disease? Neutrophil chemotaxis to complement split product C5a

The capacity of circulating phagocytes for activation by complement was investigated in consecutive, untreated cases of chronic inflammatory bowel disease. The major complement derived chemotactic factor, C5a, served as chemoattractant in dose response studies of neutrophil chemotaxis. A similar, significantly decreased sensitivity and peak response was revealed in patients with Crohn's disease and ulcerative colitis. This subnormal function of neutrophils could be shown even in cases of complete clinical remission. Chemotactic response to casein and spontaneous motility was within the normal range showing an unaffected basic cell function of neutrophils in the patients. The study shows a dysfunction of phagocytic cells, related to potentially important phlogistic mediators, in chronic inflammatory bowel disease.