Memory associated with IgA in the porcine respiratory tract

Pigs which had been immunised intraperitoneally with ovalbumin were subsequently challenged intratracheally with ovalbumin at intervals over a 200 day period. Intratracheal challenge 74 and 77 days after intraperitoneal priming resulted in a significant antigen-specific IgA response in respiratory tract secretion (RTS) on day 81. After a further 91 days, similar intratracheal challenge resulted in a lesser antigen specific IgA response in RTS. These trends were examined relative to antigen-specific IgA levels in serum and relative to antigen-specific IgG levels in serum and RTS. In addition, at the completion of the experiment the majority of anti-ovalbumin containing cells (AOCC) in the tracheal lamina propria were of the IgA class. Previously it has been shown that intratracheal challenge alone with ovalbumin had a negligible effect on AOCC in the trachea, and on specific antibody levels in respiratory tract secretion. The present findings suggest the existence of a memory mechanism operating in the porcine respiratory tract.