EXPERIMENTAL RECURRENT OTITIS-MEDIA INDUCED BY HAEMOPHILUS-INFLUENZAE- PROTECTION AND SERUM ANTIBODIES

Purpose: To study whether acute otitis media caused by encapsulated or nontypeable Haemophilus influenzae confers cross-reactive protective immunity in an animal model system and to explore the possible involve ment of various humoral specific antibodies in protection. Materials a nd Methods: Rats were intrabullarly challenged with H influenzae type b and two different nontypeable H influenzae strains. One month after the initial infection, the animals were rechallenged ipsilaterally or contralaterally with either a homologous or heterologous strain, and t he susceptibility to reinfection was investigated by otomicroscopy. Re sults: The animals challenged and rechallenged with the type b strain were well-protected ipsilaterally and contralaterally, while the prote ction after homologous rechallenge with a nontypeable strain was parti al in the ipsilateral ear and very poor in the contralateral ear, Midd le ears previously infected with a nontypeable strain remained fully s usceptible to infections with heterologous strains, but there was an i ndication of cross-protection in the animal groups where the first epi sode of acute otitis media was caused by type b and the second by a no ntypeable strain. Using the Western blot technique and an enzyme linke d immunosorbant assay, the serological response to different outer mem brane proteins, especially protein D, of H influenzae during and after middle ear infection were investigated. The serological response from the type b infected animals were generally more distinct, while the a ntibody levels against protein D were lower in these groups compared w ith the groups infected with nontypeable strains. Conclusions: These d ata indicate that H influenzae type-b-induced experimental otitis medi a results in a better protection than a nontypeable-induced, and H inf luenzae b confers a cross protection. Copyright (C) 1995 by W.B. Saund ers Company