Comparative Innate Immune Interactions of Human and Bovine Secretory IgA with Pathogenic and Non-pathogenic Bacteria

The gastrointestinal tract is colonised by a diverse population of commensal/symbiotic bacteria, which provide many metabolic functions for the host and play an important role in developing and maturing our immune system. Secretory IgA (SIgA) from milk is involved with early colonisation and maintenance of these bacteria as well as providing defence against pathogens. SIgA may bind bacteria using specific antigenic sites or non-specifically via glycans attached to the α-heavy-chain and secretory component moieties of the SIgA complex. We studied bovine SIgA for its innate binding activity with bacteria that are commonly associated with the human gastrointestinal tract and compared this activity with human SIgA. Using human and bovine SIgA isolated from milk, we incubated the proteins with a broad range of commensal, pathogenic and probiotic bacteria and measured numbers of bacteria binding SIgA, using flow cytometry. We found that human and bovine SIgA both bound similar levels of bacteria; 80 to 90% of each commensal bacteria was bound by SIgA, while levels of pathogenic and probiotic bacteria binding SIgA varied from 30 to 90%. Overall, we showed that human and bovine SIgA interacted with bacteria in a comparable way.