What is the significance of antimicrobial antibodies?

Antimicrobial antibodies are significant because

1. Although they are seen in other diseases, positive antimicrobial antibodies point towards a diagnosis of CD
2. In certain constellations,  antimicrobial antibodies characterize CD subtypes, and 
3. They predict disease course:  the greater the number of positive serological anti-microbial antigens, the greater the likelihood of more complicated disease behaviours and surgeries.

from Inflammatory Bowel Disease:  Translating Basic Science into clinical practice, Targon et al., p. 237