The Victorian Koala: Genetic Heterogeneity, Immune Responsiveness and Epizootiology of Chlamydiosis

This study was undertaken to address widely held concerns of the status of the Victorian koala. Since the identification of the Gram negative intracellular bacterium Chlamydia psittaci in koalas as being the aetiological agent of keratoconjunctivitis (causing blindness) and urogenital disease (causing female infertility), the scientific literature and media have been very inconsistent in their assessment of the impact of this disease on the koala. It was often suggested that koalas were immunologically incompetent and that this \Vas severely comprorrtlsing their ability to respond to this infection. Initially, immunochemical characterisations showed that koala immunoglobulin is remarkably similar to that of eutherian mammals including humans. Koala IgG was found to have the same basic structure consisting of two heavy y polypeptide chains ( --..s 5 kDa) linked by at least two di-sulphide bonds and two light chains ( "'25 k.Da), making up a IgG mole('ule of approximately 160 kDa. Koala IgG was also shown to have similar enzymatic digestion sites but was considerably more soluble and had a higher negative charge than eutherian IgG. This presented problems in devising purification protocols but the bacterial Fe-binding proteins Protein A and Protein G were found to be useful. Protein G was n1uch more efficient in purifying koala Ig than Protein A, although Protein A was capable of binding koala IgM. Koala IgM was shown to have a polymeric structure (probably pentameric) consisting of subunits of two heavyμ chains (,...,75 kDa) and two light chains (-25 kDa), all linked by disulphide bonds making up a structure of ....-1,000 kDa. [...]