This study has identified that P. aeruginosa produces at least three different types of corneal pathology and that not all strains are able to infect mouse corneas.

Antibodies raised against evolutionarily conserved intracytoplasmic peptide sequences of human T and B lymphocyte antigens and an antibody raised specifically against koala serum IgG were assessed for their capacity for immunoperoxidase staining of formalin fixed lymphoid tissues of koalas (Phascolarctos cinereus), common brushtail possums (Trichosurus vulpecula), common ringtail possums (Pseudocheirus peregrinus) and tammar wallabies (Macropus eugenii). Utilizing microwave pretreatment and a streptavidin biotin-horseradish peroxidase method for histochemical staining, polyclonal anti-human CD3 (for T cells), monoclonal anti-human CD5 (for T cells), monoclonal anti-human CD79b cy (for B cells) and polyclonal anti-koala IgG (for plasma cells) consistently stained lymphoid elements in a wide range of tissues from all four marsupial species. Monoclonal anti-human CD79a cy (for B cells) stained lymphoid elements in only brushtail possums. This is the first report of immunohistological staining of lymphocytes in Australian marsupials, thereby vastly increasing the scope for immunological studies in these species.

The importance of IL-4 and its effects in inflammatory bowel disease (IBD) was studied using the dextran sulphate sodium-induced model of experimental colitis. The model resembles ulcerative colitis in humans. IL-4 deficient mice and IL-4+/+ littermates were used to induce colitis. Activity of disease, extent of tissue damage, immunoglobulin isotypes, IFNgamma and IL-10 production was assessed. Both disease activity index (DAI) and histological scores were consistently lower in the IL-4 deficient mice than in the IL-4+/+ littermates. Furthermore, the lower histological scores reflected the milder inflammatory lesions and decreased ulceration found in the IL-4 deficient mice. Analysis of immunoglobulin subtypes showed that IgG1 was almost absent in the sera of IL-4 deficient mice. IFNgamma contents was much higher in colonic tissues from IL-4 deficient mice. Dextran sulphate sodium-induced colitis is ameliorated in IL-4 deficient mice. IL-4 either directly or through its effects on T and B cells influences its severity. It is unclear if the higher immunoglobulin-producing cells in the colonic tissues of IL-4 deficient mice before colitis was induced could have influenced the outcome of the disease. The high IFNgamma contents in colonic tissues of IL-4 deficient mice argue against the role of this cytokine as a crucial mediator of tissue damage during the acute phase of colitis.

An attempt was made to determine the efFect of corticosteroid on intestinal absorption and subsequent endogenous synthesis of immunoglobulins by the newborn calf. This was carried out by measuring changes in the serum concentration of IgGj, IgG2, IgM and IgA at intervals after birth in a total of 14 calves, 11 of which were born of corticosteroid-treated cows and the remainder from untreated cows. Calves were each fed 2 1 of a large volume of mixed colostrum in the first 6 hours after birth.The results indicate that corticosteroid treatment of cows induced early parturition and inhibited intestinal absorption of immunoglobulin. For the treated calves the efficiency of absorption for each immunoglobulin was half that for the untreated calves (P < 0-01). The time of onset of endogenous production of IgGj, IgGa and IgM was similar in treated and untreated calves, but the increase in serum IgA concentrations was delayed in treated calves.The practical implications of these findings are discussed.

Summary. Studies were made on the origin and mechanism of transfer of IgGj, IgG.,, IgA and IgM into the secretion of isolated loops of jejunum of unanaesthetized sheep. IgA was the major immunoglobulin in intestinal secretion, although considerable quantities of IgGj and IgG^ were also present. Secretion: serum radioactivity ratios for IgGj^ and igG^ were similar, indicating that they were transferred into intestinal secretion with equal facility. Specific radioactivities of the various immunoglobulins in serum and secretion were compared and the results suggested that all the IgGg and most of the IgGj were derived from blood plasma, whereas only a trivial amount of the IgA was plasma-derived. The slow equilibration of IgM, together with its relatively short biological 'half-life', prevented accurate assessment of plasma contribution of this immunoglobulin.INTRODUCTION.