Intestinal absorption of bacterial antigens in normal adult mice. II. A comparative study of techniques

Marked differences were seen in the oral absorption of Boivin antigen (BA) and flagellin (FLA) using antigens labelled by 3H-dinitrophenylation. Thus, after feeding 3H-DNP-FLA, a large proportion of the label was rapidly absorbed, concentrated and degraded by the liver so that no antigenic material could be recovered from the circulation. In contrast, the absorption of 3H-DNP-BA was low and slow; the absorbed material appeared stable and not readily taken up by the liver, so that 8-20% of the non-dialysable radioactivity found in the plasma was precipitable by specific antibodies. Such observations could not be made when 125I-labelled antigens were used: deiodination readily occurred in vivo, and there was re-utilization of the released label. On the other hand, using everted gut sacs, it was possible to recover 125I-labelled antigenic material after transport. A technique of measuring unlabelled antigen absorbed in the intact animal is also described, which detects antigen by combination with radioiodinated antibodies injected intravenously into the animal.