Abstract
Chlamydia pecorum is a mucosal infection, which causes debilitating disease of the urinary tract, reproductive tract and ocular sites of koalas (Phascolarctos cinereus). While antibiotics are available for treatment, they are detrimental to the koalas’ gastrointestinal tract microflora leaving the implementation of a vaccine as an ideal option for the long-term management of koala populations. We have previously reported on the successes of an anti-chlamydial recombinant major outer membrane protein (rMOMP) vaccine however, recombinant protein based vaccines are not ideal candidates for scale up from the research level to small-medium production level for wider usage. Peptide based vaccines are a promising area for vaccine development, because peptides are stable, cost effective and easily produced. In this current study, we assessed, for the first time, the immune responses to a synthetic peptide based anti-chlamydial vaccine in koalas. Five healthy male koalas were vaccinated with two synthetic peptides derived from C. pecorum MOMP and another five healthy male koalas were vaccinated with full length recombinant C. pecorum MOMP (genotype G). Systemic (IgG) and mucosal (IgA) antibodies were quantified and pre-vaccination levels compared to post-vaccination levels (12 and 26 weeks). MOMP-peptide vaccinated koalas produced Chlamydia-specific IgG and IgA antibodies, which were able to recognise not only the genotype used in the vaccination, but also MOMPs from several other koala C. pecorum genotypes. In addition, IgA antibodies induced at the ocular site not only recognised recombinant MOMP protein but also, whole native chlamydial elementary bodies. Interestingly, some MOMP-peptide vaccinated koalas showed a stronger and more sustained vaccine-induced mucosal IgA antibody response than observed in MOMP-protein vaccinated koalas. These results demonstrate that a synthetic MOMP peptide based vaccine is capable of inducing a Chlamydia-specific antibody response in koalas and is a promising candidate for future vaccine development.
Highlights
Chlamydia (C) continues to be one of the major factors threatening the long-term survival of the koala (Phascolarctos cinereus)
We present for the first time, the humoral responses in koalas vaccinated with a synthetic peptide antigen, derived from the conserved region of whole C. pecorum MOMP, combined with a Tri-Adjuvant [36]
Vaccinated koalas have shown a decrease in their chlamydial infectious load [18, 19] as well as ocular disease status [19], post-vaccination, and importantly, recombinant major outer membrane protein (rMOMP) vaccinated wild koalas have shown a decrease in the progression to disease over a 12 month period [18,19,20]
Summary
Chlamydia (C) continues to be one of the major factors threatening the long-term survival of the koala (Phascolarctos cinereus). C. pecorum is a mucosal infection, which causes debilitating disease at the urinary tract, reproductive tract and ocular sites of koalas [2]. C. pecorum infection can lead to cystitis, infertility and blindness [2,3,4,5]. The current treatment for Chlamydia in koalas involves the use of antibiotics, which can be detrimental to the koalas’ gastrointestinal tract microflora, which is essential for the digestion of their diet of eucalyptus leaves [6,7,8]. Antibiotics can be a useful treatment, they offer no long-term protection from subsequent infections and have limited effect on severe cases of chlamydiosis [9]. As Chlamydia can be asymptomatic, showing no overt signs of disease in up to 50% of infected koalas, many infected koalas go untreated [1]
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