Ig-microbiota binding patterns in mothers and infants: a scoping review

Studies characterising the immunoglobulin (Ig)-bound microbiota apply varying methodologies, making comparisons difficult. This scoping review synthesised evidence on Ig-microbiota binding patterns in maternal and infant contexts, identified recurrent Ig-bound and -unbound bacteria across studies, and highlighted knowledge gaps for further study. Nine articles investigating Ig-microbiota binding patterns in stool or breastmilk samples in mothers or infants were included. Ig-microbiota associations were influenced by sample type, Ig-subclass, genetics, and diet. The most important antibody was IgA, with partial functional redundancy with IgM, while IgG appeared more selective for pathobionts. Ig-bound taxa in early life included important commensals and pathobionts, with high levels of individuality. Ig-microbiota associations shifted with microbiome maturation, environmental and host factors, resembling adults at around 2 years of age. Transfer of Ig-bound Bifidobacterium through breastmilk may contribute to vertical transmission from mother to infant. Ig-microbiota associations also differed between health and disease states, beyond the overall microbiota. Results were limited by study numbers and a lack of methodological consistency. We propose the standardised term "Ig-Seq" in referring to the technique to study Ig-microbiota binding patterns, and suggest standardisation of laboratory protocols, bioinformatic pipelines, and statistical analyses to improve consistency in Ig-Seq.