Objective: To evaluate the prevalence of anti-neutrophil cytoplasmic antibodies in a series of patients with inflammatory bowel disease, the discriminatory value of these antibodies in differentiating between ulcerative colitis and Crohn's disease, their antigen specificity and their correlation with epidemiological and clinical variables.
Methods: Serum anti-neutrophil cytoplasmic antibodies were evaluated by indirect immunofluorescence and immunoblotting using neutrophils isolated from peripheral blood and by enzyme-linked immunosorbent assays (ELISAs) using proteinase 3 and myeloperoxidase as antigens.
Results: Anti-neutrophil cytoplasmic antibodies were detected by immunofluorescence in 43 (39.8%) of 108 patients with ulcerative colitis, in 11 (11.9%) of 92 patients with Crohn's disease (P < 0.001) and 5 (6.8%) of 73 control patients. The predominant pattern was perinuclear staining around neutrophil nuclei (44 of 59, 75%); a homogeneous cytoplasmic staining was present in 15 (25%) of 59 sera, mainly among Crohn's disease and control patients. The ELISAs gave no positive results. Recognition of proteins of relative molecular masses 27,000 and 49,000 at immunoblotting was common to ulcerative colitis, Crohn's disease and control sera. The proteins of relative molecular masses 32,000 and 106,000 were recognized exclusively by 11% of anti-neutrophil-positive ulcerative colitis sera. No significant correlation was found between the presence of anti-neutrophil cytoplasmic antibodies and the demographic and clinical characteristics of the patients.
Conclusion: Anti-neutrophil cytoplasmic antibodies are detectable in a large proportion of patients with ulcerative colitis, but their prevalence in a limited proportion of patients with Crohn's disease reduces their discriminatory capability. The persistence of anti-neutrophil cytoplasmic antibodies after total colectomy and the absence of a correlation between the activity of the disease and the presence or titre of these antibodies support the hypothesis that anti-neutrophil cytoplasmic antibodies are not simply an epiphenomenon of colonic inflammation.