MYCOPLASMA-PNEUMONIAE REINFECTION AND VACCINATION - PROTECTIVE ORAL VACCINATION AND HARMFUL IMMUNOREACTIVITY AFTER REINFECTION AND PARENTERAL IMMUNIZATION

Animal model studies of Mycoplasma pneumoniae infection after live res piratory challenge were conducted to investigate the issues of challen ge-rechallenge associated accentuated pathology, postparenteral vaccin ation associated accentuated pathology, and oral vaccination Live M. p neumoniae inocula were grown in hamster serum-based medium in order to reduce the potential for the ser um growth component to participate i n the hyperaccentuated histopathological response as seen with challen ge-rechallenge experiments which have used horse serum-based growth me dia. Despite the use of homologous animal serum, an early hyperaccentu ated response occurred (day 3 score 13.3 vs day 10 score 7.7, P = 0.02 ) which included perivascular infiltrates, and histopathological score s for early (day 3) and late (day 10) disease were similar (P > 0.10) between experiments of challenge-rechallenge when either homologous or heterologous sera were used in inoculum growth media. Parenteral vacc ination with heat-killed bacteria also led to an early hyperaccentuate d histopathological response after live respiratory challenge (scores on day 3: vaccinated 18.3, unvaccinated 6.2; P < 0.01) and this respon se was not significantly diminished when inocula were cleaned of growt h medium components. An early accentuated response did not follow oral vaccination with heat-killed bacteria (score on day 3: vaccinated 5.7 ) and the late reaction was significantly less after challenge (scores on clay 10: vaccinated 10.3, unvaccinated 14.6, P = 0.011). Studies o f parenteral vaccination should include analyses for early disease aft er live challenge. Oral vaccination offers a promising route for stimu lating protective immunity while minimizing undesirable recall immune events. Copyright (C) 1996 Elsevier Science Ltd.