PURPOSE: Fifteen percent of incident Crohn's disease (CD) cases are diagnosed at 
older ages and demonstrate colonic location and inflammatory behavior. Serologic 
responses to gut microbial antigens are associated with specific phenotypes, and 
may differ by age at diagnosis. Our aim was to identify an association between 
age at diagnosis of CD and responses to gut microbial antigens.
PATIENTS AND METHODS: Levels of anti-Saccharomyces cerevisiae antibodies (ASCA) 
immunoglobulins A and G (IgA and IgG), antibodies to Escherichia coli outer 
membrane porin-C (anti-Omp-C), antibodies to clostridial flagellin 
(anti-CBir-1), and perinuclear anti-neutrophil cytoplasmic antibodies (p-ANCA) 
were compared in patients by age in three diagnosis groups: patients diagnosed 
at ages of <40, ≥40-59, and ≥60 years. For each antigen, patients with antibody 
levels in the first, second, third, and fourth quartile were assigned a score of 
1, 2, 3, or 4, respectively. Individual scores were added to create a quartile 
sum score representing cumulative quantitative immune response.
RESULTS: Eighteen, 17, and 12 patients were diagnosed at ages <40, 40-59, and 
≥60 years, respectively. The majority (71%) had ileocolonic disease in the 
youngest group, compared to 36% in the oldest group (P=0.001). Mean ASCA IgA and 
IgG titers were increased in the youngest age group compared to the older groups 
(P=0.19 and P=0.13, respectively). Mean quartile sum scores for antibody levels 
were 7.2±2.8 in those patients diagnosed at ages <40 years, 4.9±2.9 in the 
40-59-year-old age group, and 5.6±2.6 in the ≥60-year-old age group (P=0.06).
CONCLUSION: A trend toward decreased cumulative immune responses to 
CD-associated gut antigens was observed in CD patients diagnosed at older ages 
compared to younger patients. Host responses to microbial antigens may be less 
important in older onset IBD and may contribute to the distinct phenotype in 
this group.