Food-specific immunoglobulin A does not correlate with natural tolerance to peanut or egg allergens.

ImmunoglobulinA (IgA) is the predominant antibody isotype in the gut, where it regulates commensal flora and neutralizes toxins and pathogens. The function of food-specific IgA in the gut is unknown but is presumed to protect from food allergy. Specifically, it has been hypothesized that food-specific IgA binds ingested allergens and promotes tolerance by immune exclusion; however, the evidence to support this hypothesis is indirect and mixed. Although it is known that healthy adults have peanut-specific IgA in the gut, it is unclear whether children also have gut peanut-specific IgA. We found in a cohort of non–food-allergic infants (n = 112) that there is detectable stool peanut-specific IgA that is similar to adult quantities of gut peanut-specific IgA. To investigate whether this peanut-specific IgA is associated with peanut tolerance, we examined a separate cohort of atopic children (n = 441) and found that gut peanut-specific IgA does not predict protection from development of future peanut allergy in infants nor does it correlate with concurrent oral tolerance of peanut in older children. We observed higher plasma peanut-specific IgA in those with peanut allergy. Similarly, egg white–specific IgA was detectable in infant stools and did not predict egg tolerance or outgrowth of egg allergy. Bead-based epitope assay analysis of gut peanut-specific IgA revealed similar epitope specificity between children with peanut allergy and those without; however, gut peanut-specific IgA and plasma peanut-specific IgE had different epitope specificities. These findings call into question the presumed protective role of food-specific IgA in food allergy. Rethinking IgA: The presence of food-specific IgA in the gut has historically been thought to mediate protection against IgE-mediated food allergies. However, in this study, Liu et al. provide evidence that this is not the case. The authors found that, in large cohorts of non–food-allergic infants and atopic children, there were detectable concentrations of gut peanut-specific IgA. Gut peanut-specific IgA abundance was not associated with protection against future peanut allergy, and it also did not correlate with tolerance of peanut allergy in older children. Similar findings were observed for egg white–specific IgA and development of egg allergy. Overall, these findings challenge the assumption that food-specific IgA is protective against food allergy. [ABSTRACT FROM AUTHOR]