What are the effects of Saccharomyces (S. cerevisiae) on Immunoglobulin A (IgA) and Immunoglobulin G (IgG) responses in patients with Inflammatory Bowel Disease (IBD)?

Anti-Saccharomyces cerevisiae Antibodies (ASCA) in IBD

Elevated serum anti-Saccharomyces cerevisiae IgG and IgA antibodies are characteristic serological markers in Crohn's disease patients, with significantly higher levels compared to ulcerative colitis patients and healthy controls, though their clinical utility is primarily diagnostic rather than therapeutic. 1

Antibody Patterns in IBD

IgG Response

• Serum ASCA IgG levels are significantly elevated in Crohn's disease patients compared to both ulcerative colitis patients and healthy controls. 1
• IgG4 subclass of ASCA is specifically increased in IBD patients, representing a differential immune response pattern. 2
• CD patients with severe disease phenotypes (stricturing and penetrating lesions) demonstrate slightly higher anti-microbial IgA levels, though this correlation is modest. 1

IgA Response

• Serum ASCA IgA is significantly increased in Crohn's disease patients, paralleling the IgG elevation. 1
• Anti-Saccharomyces cerevisiae IgA levels show similar patterns to IgG in distinguishing CD from UC and controls. 1

Clinical Significance and Disease Associations

Disease Activity and Phenotype

• ASCA levels do not correlate with disease activity, extent of disease, small bowel involvement, age, or gender in IBD patients. 3
• Patients with arthropathy (joint involvement) show decreased anti-food IgG levels, though anti-microbial antibody patterns remain elevated. 1
• The presence of elevated ASCA suggests that Saccharomyces cerevisiae may play a role in IBD pathophysiology, though the exact mechanism remains unclear. 3

Fecal vs. Serum Patterns

• Fecal IgG levels against microbial antigens (including S. cerevisiae) are higher in CD patients compared to controls, while fecal IgA levels are paradoxically higher in non-IBD patients. 1
• This distinct pattern between serum and fecal antibodies suggests different compartmentalized immune responses in the gut versus systemic circulation. 1

Treatment Effects on ASCA Levels

Anti-TNF Therapy

• Treatment with anti-TNF-α antibodies in CD patients significantly decreases both ASCA IgG and IgA levels, along with anti-E. coli IgG. 1
• This reduction suggests that anti-TNF therapy modulates the adaptive immune response against microbial antigens, not just inflammatory mediators. 1

Mesalazine (5-ASA)

• ASCA titers are significantly lower in Crohn's disease patients taking mesalazine compared to those not taking it, despite no difference in total serum IgG levels. 3
• This selective suppression implies mesalazine may suppress IgG production at the intestinal level rather than systemically. 3
• Corticosteroids do not affect ASCA levels in IBD patients. 3

Nutritional Therapy

• Elemental or polymeric diet therapy for Crohn's disease does not affect ASCA levels. 3

Distinction from Other Conditions

Patients with intestinal Behçet's disease show increased IgG1, IgG3, and IgG4 ASCA, representing a different pathophysiological pattern than IBD. 2

This differential subclass response may help distinguish between inflammatory bowel disease and other intestinal inflammatory conditions when clinical presentation is ambiguous. 2

Critical Pitfalls

• Do not use ASCA levels to monitor disease activity or guide treatment decisions, as they do not correlate with clinical disease severity. 3
• ASCA elevation does not indicate food intolerance—anti-food IgG and IgA levels do not correlate with food intolerance symptoms in IBD patients. 1
• The presence of ASCA does not contraindicate the use of Saccharomyces species as probiotics, though evidence for S. boulardii efficacy in IBD remains limited and requires further study. 4