IgA immune responses in the respiratory tract of pigs

Experiments were conducted in a group of pigs to determine the ontogeny of antigen specific IgA in the trachea. The results showed that following intraperitoneal immunisation with ovalbumin (OVA) there were antigen specific IgG and IgA responses in both serum and respiratory tract secretion (RTS). After intratracheal challenge the IgA response in RTS was greater than that in serum as judged by the IgA/IgG ELISA ratios. Furthermore, following intratracheal challenge the IgA/IgG RTS ratio remained elevated for about 30 days. At slaughter, the anti-OVA containing-cell (AOCC) response and the corresponding immunoglobulin class were assessed using double fluorochrome labelling techniques. Pigs challenged intratracheally on four occasions between 11 and 67 days after intraperitoneal immunisation had a population of AOCC in the trachea which was 49 +/- 15 per cent IgA. In contrast, groups of pigs intraperitoneally immunised but challenged intratracheally on fewer occasions had significantly lower proportions of AOCC that were IgA. In conjunction with previous findings these results suggest that following intraperitoneal immunisation regular antigenic challenge of the trachea over an extended period leads to an increase in the proportion of AOCC which are IgA. These results are discussed in terms of the mechanisms involved in protecting the respiratory tract.