Cell-mediated immunity in opossums(Trichosurus Vulpecula): The responses to purified protein derivative and an unrelated antigen

The roles of histology and immunohistology in the investigation of marsupial disease and normal lymphoid tissue

This review acquaints scientists with current information related to the application of histology and immunohistology to the studies of normal lymphoid tissues and specific diseases in marsupials. Histological examination of tissue is a necessary prerequisite for immunohistological examination because it establishes tissue structure and detects specific areas of disease which allow the selection of smaller areas for immunohistological examination. Information is provided on the basic techniques of histology. Immunohistology (immunohistochemistry) refers to the identification of antigenic determinants of specific substances (proteins) by the application of antibodies to histological sections. Information is provided on a technique for enzyme based, avidin-biotin enhanced immunohistology, and on antibodies that can be used to mark disease agents or marsupial tissues and cells. A summary is provided of the available information on studies of the histology and immunohistology of normal marsupial lymphoid tissue (thymus, spleen, lymph nodes and mucosa associated lymphoid tissue), and of selected marsupial diseases such as chlamydiosis and lymphosarcoma in koalas.

Immunobiology of mycobacterial infections in marsupials

Mycobacterial infections of marsupials are important for two reasons. Firstly, the Australian brushtail possum (Trichosurus vulpecula) serves as the major wildlife reservoir for Mycobacterium bovis in New Zealand and secondly, M. avium is a significant cause of disease in endangered marsupial species held in captivity. Marsupials are highly susceptible to specific mycobacterial infections which may be linked to deficiencies in their cellular immunity. Histopathological inspection of affected tissues indicates that, unlike most eutherians, marsupials are unable to wall off infection sites, resulting in formation of satellite lesions and generalised disease. This review examines possible reasons for the high susceptibility of marsupials to mycobacterial infections and investigates the prospects for developing vaccines to control these diseases.

Intracellular iron storage and the pathogenesis of paratuberculosis. Comparative studies with other mycobacterial, parasitic or infectious conditions of veterinary importance

The distribution of iron and mycobacteria was examined in the intestinal tract of ruminants with naturally-occurring M. paratuberculosis infection and compared with mycobacterial infections in several species. This distribution was compared with that of iron in chronic lesions caused by other microbial or parasitic agents. In the clinical form of paratuberculosis in cattle, sheep and goats there was marked lymphangiectasis and a high proportion of the granulomatous lesions contained siderotic macrophages with a high mycobacterial content. In cattle with preclinical lesions of granulomatous enteropathy, the greatest number of acid-fast organisms was present in siderotic, non-differentiated, ileo-caecal macrophages; concurrent mast cell-associated allergic enteropathy was also apparent in the duodenum, proximal and mid-ileum of most animals. In paratuberculosis-affected herds, a high proportion of non-productive cows were without classical granulomatous change but had cultural or immunological evidence of M. paratuberculosis infection and similar allergic catarrhal enteropathy of the upper intestinal tract. Interstitial haemorrhage of the ileocaecal valve, with the accumulation of haemosiderin and ferritin in undifferentiated macrophages was observed in some of these cattle and also in others with experimentally-induced copper deficiency and acute ostertagiasis. Colonisation of the ileo-caecal or caecal glandular crypts by large, apparently saprophytic acid-fast organisms indicated regional tolerance to such organisms in all cattle. In other mycobacterioses such as bovine or avian tuberculosis, undifferentiated, siderotic macrophages containing mycobacteria were also seen in early granulomas, but epithelioid and giant cell differentiation invariably led to the disappearance of intracellular iron and a reduction in mycobacterial numbers. In possums in which epithelioid and giant cells did not occur in response to M. bovis infection, siderosis persisted in many macrophages and overwhelming mycobacterial multiplication occurred. These studies indicate that, in most infections with mycobacteria, differentiation of macrophages radically reverses their iron acquisitive properties, creating an intracellular environment unsuitable for mycobacterial multiplication. It seems likely that allergically mediated microvascular haemorrhage, local tolerance of commensal mycobacteria and attenuation of the macrophage siderosis reversal mechanism provide unique conditions for early, uninhibited, intracellular multiplication of M. paratuberculosis in the ileo-caecal valve of certain mature ruminants.

Absence of lymphokine-enhanced macrophage migration in vitro in the Australian brush-tailed opossum, Trichosurus vulpecula

The supernatants from cultures of either opossum or guinea pig splenic lymphocytes, stimulated with phytohaemagglutinin, significantly enhanced the in vitro migration of guinea pig peritoneal macrophages (P greater than 0.001) but not that of opossum peritoneal macrophages. Failure of opossum macrophages to respond to a putative macrophage chemotactic factor might account for the observed paucity of immune granulomas in these animals and help explain the species' susceptibility to tuberculosis.