What is the significance of positive ASCA?

What are Anti-saccharomyces cerevisiae antibodies?

Relationship to Celiac Disease

Antibodies anti-Saccharomyces cerevisiae (ASCA) do not differentiate Crohn's disease from celiac disease in Arquivos de Gastroenterologia (2010)
From the article:

"The protective function of the intestinal mucosa is called "permeability"(12). When the intestinal mucosal barrier is broken, with junctions-mediated barrier defects, an influx of luminal antigens may result in inflammation, even by chronically stimulating resident, with consequent recruitement of immunocompetent cells from the lamina propria(3, 7). In patients with autoimmune diseases, like CD, or in infectious disease, and in various other clinical conditions, ASCA can be positive. The presence of ASCA may reflect a shared permeability disorder, leading to the enhanced exposure to various antigens that, depending on the genetic background, may provoke various or multiple autoimmune disorders.(3, 4, 5, 7, 9, 14). The antibodies in the sera of the analysed ASCA positive cases proved a systemic immune response against Sacharomyces cerevisiae (generally accepted as not a pathogen) and suggested the end of the oral tolerance against the yeast's antigens(3).  ...
In conclusion, the results show that ASCA was found in patients with CeD and disappear after a GFD. So, it is presumed that ASCA positivity is not a specific marker for Crohn's disease but correlates with the (auto) immune inflammation of the small intestine."

Relationship to CD subtype

"Serologic Investigations in Children with Inflammatory Bowel Disease and Food Allergy" in Mediators of Inflammation (2009)
" The occurrence of ASCA antibodies (IgA and/or IgG) was observed in 73.7% of children with Crohn’s disease, 17.5% with ulcerative colitis and almost 30% with allergic colitis, statistically significantly more frequent in children with Crohn’s disease in comparison with the other examined groups and controls. Statistically, patients with Crohn’s disease and the presence of ASCA revealed a significantly more frequent localization of lesions within the small bowel and a tendency towards older age (mean age 15.5). Sensitivity ASCA (IgG or IgA) for diagnosing Crohn’s disease was determined as 73.7%, specificity (in relation to controls) was 91.3%.
... In our examination we found a relation between the examined mutations of gene NOD2/CARD15 and the presence of antibodies. Similary Annese in a large group of patients with Crohn’s disease proved a relation between mutation NOD2/CARD15 and the localization in the small bowel, the narrowing form of the disease and the early age of diagnosis, but she also showed a relation between the mutation and the presence of ASCA [31]. The presence of ASCA is important for patients with undetermined colitis, however, 50% of these patients do not produce ASCA and p-ANCA."

"Genetic variants of the mannan-binding lectin are associated with immune reactivity to mannans in Crohn’s disease" in Gastroenterology (2004)
"Conclusions: A subgroup of CD patients is characterized by ASCA positivity, T-cell proliferation on mannan stimulation, and mutations in the MBL gene that result in MBL deficiency. Thus, we propose that enhanced mannan exposure stimulates specific immune responses in a subgroup of CD patients with genetically determined low MBL concentrations. This enhanced exposure contributes to the generation of ASCA."