Abstract
Simple SummaryChlamydia is a major pathogen of the Australian marsupial, the koala (Phascolarctos cinereus). One approach to improving this situation is to develop a vaccine. Human Chlamydia research suggests that an effective anti-chlamydial response will involve a balance between a cell-mediated Th1 response and a humoral Th2 responses, involving systemic IgG and mucosal IgA. Characterization of koalas with chlamydial disease suggests that increased expression for similar immunological pathways and monitoring of koalas’ post-vaccination can be successful and subsequently lead to improved vaccines. These findings offer optimism that a chlamydial vaccine for wider distribution to koalas is not far off.Chlamydia is a significant pathogen for many species, including the much-loved Australian marsupial, the koala (Phascolarctos cinereus). To combat this situation, focused research has gone into the development and refinement of a chlamydial vaccine for koalas. The foundation of this process has involved characterising the immune response of koalas to both natural chlamydial infection as well as vaccination. From parallels in human and mouse research, it is well-established that an effective anti-chlamydial response will involve a balance of cell-mediated Th1 responses involving interferon-gamma (IFN-γ), humoral Th2 responses involving systemic IgG and mucosal IgA, and inflammatory Th17 responses involving interleukin 17 (IL-17) and neutrophils. Characterisation of koalas with chlamydial disease has shown increased expression within all three of these major immunological pathways and monitoring of koalas’ post-vaccination has detected further enhancements to these key pathways. These findings offer optimism that a chlamydial vaccine for wider distribution to koalas is not far off. Recent advances in marsupial genetic knowledge and general nucleic acid assay technology have moved koala immunological research a step closer to other mammalian research systems. However, koala-specific reagents to directly assay cytokine levels and cell-surface markers are still needed to progress our understanding of koala immunology.
Highlights
Simple Summary: Chlamydia is a major pathogen of the Australian marsupial, the koala (Phascolarctos cinereus)
Characterisation of koalas with chlamydial disease has shown increased expression within all three of these major immunological pathways and monitoring of koalas’ post-vaccination has detected further enhancements to these key pathways. These findings offer optimism that a chlamydial vaccine for wider distribution to koalas is not far off
Immunogenetic studies have found links between chlamydial infections/complications and human leukocyte antigen (HLA) alleles from both classes, with examples including the presence of alleles from HLA class I A and C loci having significantly higher risk of C. trachomatis pelvic inflammatory disease [22] and the HLA class II HLA-DQB1*06 allele emerging as a significant risk marker for chlamydia reinfection in African American women [23]
Summary
Chlamydia are obligate intracellular bacteria recognised in a wide range of hosts. Traditionally identified and studied in birds, cattle, guinea pigs, sheep and humans [1], continued research has expanded the list of chlamydial hosts to include insects, amphibians, molluscs, arachnids, reptiles, fish, and amoeba, as well as mammals like pigs, goats, deer, cats, bats, possums, and koalas [2]. Chlamydial infection in koalas is dominated by the species Chlamydia pecorum These infections lead to ocular and urogenital/reproductive diseases comparable to Chlamydia trachomatis infections in humans, which include keratoconjunctivitis and scarring in the eye leading to blindness and cystitis/nephritis and Animals 2021, 11, x reproductive cysts in the urogenital and reproductive tracts, respectively, leading to severe pain and infertility [3,4]. Research has highlighted many many similarities in immune responses to Chlamydia infectionbetween betweenhosts, hosts, allowing allowing for similarities in immune responses to Chlamydia infection for knowledge research in in others This hashas proven advantageous to the knowledgefrom fromone onehost hosttotoguide guide research others. The koala in field the field of chlamydial immune responses vaccine development
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