Acute otitis media is the most common illness diagnosed during early childhood that
can cause significant morbidity (Brook, 1994) and sometimes can cause irreversible
sequelae such as a hearing defect and subsequent learning difficulties (Klein, 1994). The
aims of the research presented here were to study some aspects of the middle ear
defence mechanisms in both immune and non-immune rats following experimental
otitis media (OM) with two pathogens nontypeable Haemophilus influenzae (NTHi) and
Moraxella catarrhalis (M. catarrhalis). This study also aimed at developing a suitable
technique for preparing immunohistochemical staining of middle ear sections (chapter
2).
A previous study has shown that a regime where rats received an IPP immunisation
combined with an IT boost was effective in enhancing clearance of a middle ear
infection with the same strain of NTHi and also in the presence of a concomitant viral
infection (Moore et al, 2001). Results of this study have shown that for NTHi infection
a distinct cellular influx to the middle ear in the immune rats was accompanied by an
enhanced bacterial clearance compared to the non-immunised rats (chapter 3). This
cellular influx was responsible for the remarkable reduction in the bacterial number.
The sharp decline in PMNs numbers in the NTHi immunised rats that followed
complete bacterial clearance at 72h post infection (Table 3.1) indicate a more
effectively controlled down regulation of this cell infiltrate than the non-immunised rats.
For M. catarrhalis infection, there was no difference in cell infiltrate between immune
and non-immune rats, but enhanced clearance of the bacteria were observed for the
immune animals.
The histopathological changes in the middle ear mucosa of rats with experimentally
induced infection were studied to provide a better understanding about the distribution
of the inflammatory cells and changes in the mucosa during the first 24h post challenge
with NTHi and M. catarrhalis (Chapter 4). These changes have not been previously
studied for the two pathogens at 24h post challenge in rats. Induced infections with the
two pathogens were found to produce similar histopathological changes but more
inflammatory infiltration was observed within the infected mucosa with NTHi than that
seen with M. catarrhalis. The infections were characterized by increased thickness of
the middle ear mucosa, Eustachian tube mucosa, periosteum and tympanic membrane.
There was also an increase in the number and size of small blood vessels at all sites, and
these small blood vessels seem to be the source of the inflammatory infiltration into the
middle ear mucosa and middle ear cavity during the infection. These findings provided
an essential background to the immunohistochemical study.
The effect of mucosal immunisation on the distribution of CD4+T cells and CD8+T
cells has not been investigated previously. Results of the present study (Chapter 5) show
the pattern of distribution of these cells during the first 48h post infection with NTHi in
the rat. The number of CD4+and CD8+T cells peaked at 24h post infection in the nonimmunised
animal and were highest at 48h post-infection in the immunised rats. The
difference in response in the immunised rats may represent regulation of the
inflammatory response by the immune system. The inflammatory response regulation is
indicated by the difference in cellular influx into the immune rats and the response in
the immune rats that corresponds to enhanced bacterial clearance prior to a decrease in
numbers of inflammatory cells once the bacteria was no longer detected (Chapter 3).
This resolution of the inflammatory mass would reduce the opportunity for continued
damage to local tissue. These changes are also supported by the reduction in the
thickness of the middle ear mucosa of the immunised rats especially at 24h and 48h
post-infection (Chapter 5).
This study has shown that there are distinct differences in the rate of bacterial clearance
and cellular changes in the middle ear mucosa and tympanic bulla in immunised rats
during a middle ear infection. Future studies are still required to gain a better
understanding of differences in the inflammatory response for both pathogens, NTHi
and M. catarrhalis.
| Identifer | oai:union.ndltd.org:ADTP/219308 |
| Date | January 2002 |
| Creators | Saleh, Nadeh S., n/a |
| Publisher | University of Canberra. Applied Science |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | ), Copyright Nadeh S. Saleh |
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