Evolution has provided effective ways of protecting man from external dangers while prospering from opportunities. The gut microbiota is a complex mixture of microbes that are continuously challenging the integrity of the intestinal barrier while at the same time providing numerous metabolic advantages. The intestinal barrier integrity is ensured by various mechanisms including host antibodies in the form of secretory IgA (sIgA). sIgA binds microbes and regulate microbiota ecology. Patients suffering from IgA deficiency display altered microbiota ecology and increased risk of infection. Our project will provide preclinical evaluation of a therapeutic approach aiming to reconstitute IgA in immune deficient individuals. This will provide a better insight into the role of IgA in regulating host - gut microbiota interactions and potentially provide evidence for a protective therapy in immunodeficient pathologies, such as primary as well as corticosteroid induced immunodeficiencies.