Commensal bacteria coated by secretory immunoglobulin A and immunoglobulin G in the gastrointestinal tract of pigs and calves.

A large amount of secretory immunoglobulin A (S-IgA) is secreted in the alimentary tract of mammals. It has been reported that S-IgA coats a portion of commensal intestinal bacteria in human and mouse. However, S-IgA-coated bacteria have not been studied in pigs and calves. In this study, we evaluated the distribution of S-IgA-coated commensal intestinal bacteria in each portion of the gastrointestinal tracts of pigs and calves. Immunoglobulin G (IgG)-coated bacteria were also analyzed because a considerable amount of IgG is secreted in the gastrointestinal tracts of pigs, and in particular, calves. S-IgA- or IgG-coated bacteria were detected in all the segments of the gastrointestinal tracts of pigs and calves. The proportion of S-IgA-coated bacteria to total bacteria (i.e. S-IgA coating ratio) varied in the segments of the gastrointestinal tract in pigs, whereas those of calves were nearly the same throughout the gastrointestinal tract. The S-IgA and IgG coating ratios were higher in pigs than in calves for all segments of the gastrointestinal tract.