CD40LG and hyperinsulinemic hypoglycemia, familial, 4: Indeed, IgA deficiency usually leads to a substantial increase in the intestinal IgM+ ASC and IgM levels in humans.116 Only those with compensatory IgM secretion show a normal GM compared to IgA-sufficient individuals.117 In summary, it appears that the most abundant antibody in breast milk, SIgA, plays a fundamental role in regulating GM and immunity in the neonatal gut.